diff --git a/Makefile b/Makefile
index d7dc14b4e7e28..453f32eed9b38 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,5 @@
 
-BINARIES=bin/buildd-standalone bin/buildd-containerd bin/buildctl	bin/buildctl-darwin bin/buildd.exe bin/buildctl.exe
+BINARIES=bin/buildd bin/buildd-standalone bin/buildd-containerd bin/buildctl	bin/buildctl-darwin bin/buildd.exe bin/buildctl.exe
 
 binaries: $(BINARIES)
 
diff --git a/cmd/buildd/main.go b/cmd/buildd/main.go
index 48f0fd6be7d21..7b043d3278d85 100644
--- a/cmd/buildd/main.go
+++ b/cmd/buildd/main.go
@@ -5,10 +5,16 @@ import (
 	"net"
 	"os"
 	"path/filepath"
+	"sort"
 	"strings"
 
 	"github.com/containerd/containerd/sys"
 	"github.com/docker/go-connections/sockets"
+	"github.com/moby/buildkit/control"
+	"github.com/moby/buildkit/frontend"
+	"github.com/moby/buildkit/frontend/dockerfile"
+	"github.com/moby/buildkit/frontend/gateway"
+	"github.com/moby/buildkit/metaworker"
 	"github.com/moby/buildkit/util/appcontext"
 	"github.com/moby/buildkit/util/appdefaults"
 	"github.com/moby/buildkit/util/profiler"
@@ -20,6 +26,12 @@ import (
 	"google.golang.org/grpc"
 )
 
+var (
+	appFlags []cli.Flag
+	// key: priority (+: less preferred, -: more preferred)
+	metaWorkerCtors = make(map[int]func(c *cli.Context, root string) ([]*metaworker.MetaWorker, error), 0)
+)
+
 func main() {
 	app := cli.NewApp()
 	app.Name = "buildd"
@@ -45,9 +57,14 @@ func main() {
 			Usage: "debugging address (eg. 0.0.0.0:6060)",
 			Value: "",
 		},
+		cli.StringFlag{
+			Name:  "default-worker",
+			Usage: "default worker name (eg. containerd-overlay)",
+			Value: "",
+		},
 	}
 
-	app.Flags = appendFlags(app.Flags)
+	app.Flags = append(app.Flags, appFlags...)
 
 	app.Action = func(c *cli.Context) error {
 		ctx, cancel := context.WithCancel(appcontext.Context())
@@ -179,3 +196,54 @@ func unaryInterceptor(globalCtx context.Context) grpc.ServerOption {
 		return
 	})
 }
+
+func newController(c *cli.Context, root string) (*control.Controller, error) {
+	mws, err := metaWorkers(c, root)
+	if err != nil {
+		return nil, err
+	}
+	frontends := map[string]frontend.Frontend{}
+	frontends["dockerfile.v0"] = dockerfile.NewDockerfileFrontend()
+	frontends["gateway.v0"] = gateway.NewGatewayFrontend()
+	return control.NewController(control.Opt{
+		MetaWorkers: mws,
+		Frontends:   frontends,
+	})
+}
+
+func metaWorkers(c *cli.Context, root string) ([]*metaworker.MetaWorker, error) {
+	defaultWorkerName := c.GlobalString("default-worker")
+	type ctorEntry struct {
+		priority int
+		ctor     func(c *cli.Context, root string) ([]*metaworker.MetaWorker, error)
+	}
+	var ctors []ctorEntry
+	for p, ctor := range metaWorkerCtors {
+		ctors = append(ctors, ctorEntry{priority: p, ctor: ctor})
+	}
+	sort.Slice(ctors, func(i, j int) bool { return ctors[i].priority < ctors[j].priority })
+	var ret []*metaworker.MetaWorker
+	for _, e := range ctors {
+		mws, err := e.ctor(c, root)
+		if err != nil {
+			return ret, err
+		}
+		for _, mw := range mws {
+			logrus.Infof("Found worker %q", mw.Name)
+			ret = append(ret, mw)
+			if defaultWorkerName == mw.Name {
+				last := len(ret) - 1
+				ret[0], ret[last] = ret[last], ret[0]
+			}
+		}
+	}
+	if len(ret) == 0 {
+		return nil, errors.New("no worker found, build the buildkit daemon with tags? (e.g. \"standalone\", \"containerd\")")
+	}
+	if defaultWorkerName != "" && defaultWorkerName != ret[0].Name {
+		return nil, errors.Errorf("worker %q not found", defaultWorkerName)
+	}
+	logrus.Infof("Found %d workers, default=%q", len(ret), ret[0].Name)
+	logrus.Warn("Currently, only the default worker can be used.")
+	return ret, nil
+}
diff --git a/cmd/buildd/main_containerd.go b/cmd/buildd/main_containerd.go
index e711f5bbdb164..e5f7d50a7c5dd 100644
--- a/cmd/buildd/main_containerd.go
+++ b/cmd/buildd/main_containerd.go
@@ -1,25 +1,62 @@
-// +build containerd,!standalone
+// +build containerd
 
 package main
 
 import (
-	"github.com/moby/buildkit/control"
+	"os"
+	"strings"
+
+	"github.com/moby/buildkit/metaworker"
+	"github.com/moby/buildkit/metaworker/containerd"
+	"github.com/sirupsen/logrus"
 	"github.com/urfave/cli"
 )
 
-func appendFlags(f []cli.Flag) []cli.Flag {
-	return append(f, []cli.Flag{
+func init() {
+	appFlags = append(appFlags,
+		cli.BoolFlag{
+			Name:  "disable-containerd",
+			Usage: "disable containerd workers",
+		},
 		cli.StringFlag{
 			Name:  "containerd",
 			Usage: "containerd socket",
 			Value: "/run/containerd/containerd.sock",
-		},
-	}...)
+		})
+	// 1 is less preferred than 0 (runcCtor)
+	metaWorkerCtors[1] = containerdCtor
 }
 
-// root must be an absolute path
-func newController(c *cli.Context, root string) (*control.Controller, error) {
+func containerdCtor(c *cli.Context, root string) ([]*metaworker.MetaWorker, error) {
 	socket := c.GlobalString("containerd")
+	if c.GlobalBool("disable-containerd") || skipContainerd(socket) {
+		return nil, nil
+	}
+	opts, err := containerd.NewMetaWorkerOpts(root, socket)
+	if err != nil {
+		return nil, err
+	}
+	var mws []*metaworker.MetaWorker
+	for _, opt := range opts {
+		mw, err := metaworker.NewMetaWorker(opt)
+		if err != nil {
+			return mws, err
+		}
+		mws = append(mws, mw)
+	}
+	return mws, nil
+}
 
-	return control.NewContainerd(root, socket)
+func skipContainerd(socket string) bool {
+	if strings.HasPrefix(socket, "tcp://") {
+		// FIXME(AkihiroSuda): prohibit tcp?
+		return false
+	}
+	socketPath := strings.TrimPrefix(socket, "unix://")
+	if _, err := os.Stat(socketPath); os.IsNotExist(err) {
+		// FIXME(AkihiroSuda): add more conditions
+		logrus.Warnf("skipping containerd, as %q does not exist", socketPath)
+		return true
+	}
+	return false
 }
diff --git a/cmd/buildd/main_standalone.go b/cmd/buildd/main_standalone.go
index 83a3818fa2717..7b566194b5dcc 100644
--- a/cmd/buildd/main_standalone.go
+++ b/cmd/buildd/main_standalone.go
@@ -1,17 +1,39 @@
-// +build standalone,!containerd
+// +build standalone
+
+// TODO(AkihiroSuda): s/standalone/oci/g ?
 
 package main
 
 import (
-	"github.com/moby/buildkit/control"
+	"github.com/moby/buildkit/metaworker"
+	"github.com/moby/buildkit/metaworker/runc"
 	"github.com/urfave/cli"
 )
 
-func appendFlags(f []cli.Flag) []cli.Flag {
-	return f
+func init() {
+	appFlags = append(appFlags,
+		cli.BoolFlag{
+			Name:  "disable-runc",
+			Usage: "disable runc workers",
+		})
+	metaWorkerCtors[0] = runcCtor
 }
 
-// root must be an absolute path
-func newController(c *cli.Context, root string) (*control.Controller, error) {
-	return control.NewStandalone(root)
+func runcCtor(c *cli.Context, root string) ([]*metaworker.MetaWorker, error) {
+	if c.GlobalBool("disable-runc") {
+		return nil, nil
+	}
+	opts, err := runc.NewMetaWorkerOpts(root)
+	if err != nil {
+		return nil, err
+	}
+	var mws []*metaworker.MetaWorker
+	for _, opt := range opts {
+		mw, err := metaworker.NewMetaWorker(opt)
+		if err != nil {
+			return mws, err
+		}
+		mws = append(mws, mw)
+	}
+	return mws, nil
 }
diff --git a/cmd/buildd/main_unsupported.go b/cmd/buildd/main_unsupported.go
deleted file mode 100644
index ca53dcd51ca1a..0000000000000
--- a/cmd/buildd/main_unsupported.go
+++ /dev/null
@@ -1,18 +0,0 @@
-// +build !standalone,!containerd standalone,containerd
-
-package main
-
-import (
-	"errors"
-
-	"github.com/moby/buildkit/control"
-	"github.com/urfave/cli"
-)
-
-func appendFlags(f []cli.Flag) []cli.Flag {
-	return f
-}
-
-func newController(c *cli.Context, root string) (*control.Controller, error) {
-	return nil, errors.New("need to build daemon with either standalone or containerd build tag")
-}
diff --git a/control/control.go b/control/control.go
index b62fae0128ce3..6a6ae3d9007c7 100644
--- a/control/control.go
+++ b/control/control.go
@@ -1,19 +1,15 @@
 package control
 
 import (
-	"github.com/containerd/containerd/snapshots"
 	"github.com/docker/distribution/reference"
 	controlapi "github.com/moby/buildkit/api/services/control"
-	"github.com/moby/buildkit/cache"
-	"github.com/moby/buildkit/cache/cacheimport"
 	"github.com/moby/buildkit/client"
 	"github.com/moby/buildkit/exporter"
 	"github.com/moby/buildkit/frontend"
+	"github.com/moby/buildkit/metaworker"
 	"github.com/moby/buildkit/session"
 	"github.com/moby/buildkit/session/grpchijack"
 	"github.com/moby/buildkit/solver"
-	"github.com/moby/buildkit/source"
-	"github.com/moby/buildkit/worker"
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
 	"golang.org/x/net/context"
@@ -22,17 +18,9 @@ import (
 )
 
 type Opt struct {
-	Snapshotter      snapshots.Snapshotter
-	CacheManager     cache.Manager
-	Worker           worker.Worker
-	SourceManager    *source.Manager
-	InstructionCache solver.InstructionCache
-	Exporters        map[string]exporter.Exporter
-	SessionManager   *session.Manager
-	Frontends        map[string]frontend.Frontend
-	ImageSource      source.Source
-	CacheExporter    *cacheimport.CacheExporter
-	CacheImporter    *cacheimport.CacheImporter
+	MetaWorkers []*metaworker.MetaWorker
+	Frontends   map[string]frontend.Frontend
+	// TODO: split more from metaworkers
 }
 
 type Controller struct { // TODO: ControlService
@@ -44,14 +32,8 @@ func NewController(opt Opt) (*Controller, error) {
 	c := &Controller{
 		opt: opt,
 		solver: solver.NewLLBSolver(solver.LLBOpt{
-			SourceManager:    opt.SourceManager,
-			CacheManager:     opt.CacheManager,
-			Worker:           opt.Worker,
-			InstructionCache: opt.InstructionCache,
-			ImageSource:      opt.ImageSource,
-			Frontends:        opt.Frontends,
-			CacheExporter:    opt.CacheExporter,
-			CacheImporter:    opt.CacheImporter,
+			MetaWorkers: opt.MetaWorkers,
+			Frontends:   opt.Frontends,
 		}),
 	}
 	return c, nil
@@ -63,7 +45,9 @@ func (c *Controller) Register(server *grpc.Server) error {
 }
 
 func (c *Controller) DiskUsage(ctx context.Context, r *controlapi.DiskUsageRequest) (*controlapi.DiskUsageResponse, error) {
-	du, err := c.opt.CacheManager.DiskUsage(ctx, client.DiskUsageInfo{
+	// FIXME mw0
+	mw0 := c.opt.MetaWorkers[0]
+	du, err := mw0.CacheManager.DiskUsage(ctx, client.DiskUsageInfo{
 		Filter: r.Filter,
 	})
 	if err != nil {
@@ -101,8 +85,10 @@ func (c *Controller) Solve(ctx context.Context, req *controlapi.SolveRequest) (*
 
 	var expi exporter.ExporterInstance
 	var err error
+	// FIXME mw0
+	mw0 := c.opt.MetaWorkers[0]
 	if req.Exporter != "" {
-		exp, ok := c.opt.Exporters[req.Exporter]
+		exp, ok := mw0.Exporters[req.Exporter]
 		if !ok {
 			return nil, errors.Errorf("exporter %q could not be found", req.Exporter)
 		}
@@ -202,7 +188,9 @@ func (c *Controller) Session(stream controlapi.Control_SessionServer) error {
 	logrus.Debugf("session started")
 	conn, opts := grpchijack.Hijack(stream)
 	defer conn.Close()
-	err := c.opt.SessionManager.HandleConn(stream.Context(), conn, opts)
+	// FIXME mw0
+	mw0 := c.opt.MetaWorkers[0]
+	err := mw0.SessionManager.HandleConn(stream.Context(), conn, opts)
 	logrus.Debugf("session finished: %v", err)
 	return err
 }
diff --git a/control/control_containerd.go b/control/control_containerd.go
deleted file mode 100644
index 63a2a16b55dd6..0000000000000
--- a/control/control_containerd.go
+++ /dev/null
@@ -1,86 +0,0 @@
-// +build containerd
-
-package control
-
-import (
-	"context"
-	"fmt"
-	"net"
-	"os"
-	"strings"
-	"time"
-
-	"github.com/containerd/containerd"
-	"github.com/containerd/containerd/content"
-	"github.com/moby/buildkit/worker/containerdworker"
-	digest "github.com/opencontainers/go-digest"
-	"github.com/pkg/errors"
-)
-
-func NewContainerd(root, address string) (*Controller, error) {
-	if err := os.MkdirAll(root, 0700); err != nil {
-		return nil, errors.Wrapf(err, "failed to create %s", root)
-	}
-
-	// TODO: take lock to make sure there are no duplicates
-	client, err := containerd.New(address, containerd.WithDefaultNamespace("buildkit"))
-	if err != nil {
-		return nil, errors.Wrapf(err, "failed to connect client to %q . make sure containerd is running", address)
-	}
-
-	pd := newContainerdPullDeps(client)
-
-	opt, err := defaultControllerOpts(root, *pd)
-	if err != nil {
-		return nil, err
-	}
-
-	opt.Worker = containerdworker.New(client)
-
-	return NewController(*opt)
-}
-
-func newContainerdPullDeps(client *containerd.Client) *pullDeps {
-	diff := client.DiffService()
-	return &pullDeps{
-		Snapshotter:  client.SnapshotService(containerd.DefaultSnapshotter),
-		ContentStore: &noGCContentStore{client.ContentStore()},
-		Applier:      diff,
-		Differ:       diff,
-		Images:       client.ImageService(),
-	}
-}
-
-func dialer(address string, timeout time.Duration) (net.Conn, error) {
-	address = strings.TrimPrefix(address, "unix://")
-	return net.DialTimeout("unix", address, timeout)
-}
-
-func dialAddress(address string) string {
-	return fmt.Sprintf("unix://%s", address)
-}
-
-// TODO: Replace this with leases
-
-type noGCContentStore struct {
-	content.Store
-}
-type noGCWriter struct {
-	content.Writer
-}
-
-func (cs *noGCContentStore) Writer(ctx context.Context, ref string, size int64, expected digest.Digest) (content.Writer, error) {
-	w, err := cs.Store.Writer(ctx, ref, size, expected)
-	return &noGCWriter{w}, err
-}
-
-func (w *noGCWriter) Commit(ctx context.Context, size int64, expected digest.Digest, opts ...content.Opt) error {
-	opts = append(opts, func(info *content.Info) error {
-		if info.Labels == nil {
-			info.Labels = map[string]string{}
-		}
-		info.Labels["containerd.io/gc.root"] = time.Now().UTC().Format(time.RFC3339Nano)
-		return nil
-	})
-	return w.Writer.Commit(ctx, size, expected, opts...)
-}
diff --git a/control/control_standalone_test.go b/control/control_standalone_test.go
deleted file mode 100644
index 60acbb15590bd..0000000000000
--- a/control/control_standalone_test.go
+++ /dev/null
@@ -1,174 +0,0 @@
-// +build linux,standalone
-
-package control
-
-import (
-	"bytes"
-	"io"
-	"io/ioutil"
-	"os"
-	"os/exec"
-	"path/filepath"
-	"testing"
-
-	"github.com/containerd/containerd/namespaces"
-	"github.com/moby/buildkit/cache"
-	"github.com/moby/buildkit/cache/metadata"
-	"github.com/moby/buildkit/client"
-	"github.com/moby/buildkit/snapshot"
-	"github.com/moby/buildkit/snapshot/blobmapping"
-	"github.com/moby/buildkit/source"
-	"github.com/moby/buildkit/source/containerimage"
-	"github.com/moby/buildkit/worker"
-	"github.com/moby/buildkit/worker/runcworker"
-	"github.com/stretchr/testify/assert"
-	"golang.org/x/net/context"
-)
-
-func TestControlStandalone(t *testing.T) {
-	if os.Getuid() != 0 {
-		t.Skip("requires root")
-	}
-	if _, err := exec.LookPath("runc"); err != nil {
-		t.Skipf("no runc found: %s", err.Error())
-	}
-
-	ctx := namespaces.WithNamespace(context.Background(), "buildkit-test")
-
-	// this should be an example or e2e test
-	tmpdir, err := ioutil.TempDir("", "controltest")
-	assert.NoError(t, err)
-	defer os.RemoveAll(tmpdir)
-
-	cd, err := newStandalonePullDeps(tmpdir)
-	assert.NoError(t, err)
-
-	md, err := metadata.NewStore(filepath.Join(tmpdir, "metadata.db"))
-	assert.NoError(t, err)
-
-	snapshotter, err := blobmapping.NewSnapshotter(blobmapping.Opt{
-		Content:       cd.ContentStore,
-		Snapshotter:   cd.Snapshotter,
-		MetadataStore: md,
-	})
-	assert.NoError(t, err)
-
-	cm, err := cache.NewManager(cache.ManagerOpt{
-		Snapshotter:   snapshotter,
-		MetadataStore: md,
-	})
-	assert.NoError(t, err)
-
-	sm, err := source.NewManager()
-	assert.NoError(t, err)
-
-	is, err := containerimage.NewSource(containerimage.SourceOpt{
-		Snapshotter:   snapshotter,
-		ContentStore:  cd.ContentStore,
-		Applier:       cd.Applier,
-		CacheAccessor: cm,
-	})
-	assert.NoError(t, err)
-
-	sm.Register(is)
-
-	img, err := source.NewImageIdentifier("docker.io/library/busybox:latest")
-	assert.NoError(t, err)
-
-	src, err := sm.Resolve(ctx, img)
-	assert.NoError(t, err)
-
-	snap, err := src.Snapshot(ctx)
-	assert.NoError(t, err)
-
-	mounts, err := snap.Mount(ctx, false)
-	assert.NoError(t, err)
-
-	lm := snapshot.LocalMounter(mounts)
-
-	target, err := lm.Mount()
-	assert.NoError(t, err)
-
-	f, err := os.Open(target)
-	assert.NoError(t, err)
-
-	names, err := f.Readdirnames(-1)
-	assert.NoError(t, err)
-	assert.True(t, len(names) > 5)
-
-	err = f.Close()
-	assert.NoError(t, err)
-
-	lm.Unmount()
-	assert.NoError(t, err)
-
-	du, err := cm.DiskUsage(ctx, client.DiskUsageInfo{})
-	assert.NoError(t, err)
-
-	// for _, d := range du {
-	// 	fmt.Printf("du: %+v\n", d)
-	// }
-
-	for _, d := range du {
-		assert.True(t, d.Size >= 8192)
-	}
-
-	w, err := runcworker.New(tmpdir)
-	assert.NoError(t, err)
-
-	meta := worker.Meta{
-		Args: []string{"/bin/sh", "-c", "echo \"foo\" > /bar"},
-		Cwd:  "/",
-	}
-
-	stderr := bytes.NewBuffer(nil)
-
-	err = w.Exec(ctx, meta, snap, nil, nil, nil, &nopCloser{stderr})
-	assert.Error(t, err) // Read-only root
-	// typical error is like `mkdir /.../rootfs/proc: read-only file system`.
-	// make sure the error is caused before running `echo foo > /bar`.
-	assert.Contains(t, stderr.String(), "read-only file system")
-
-	root, err := cm.New(ctx, snap)
-	assert.NoError(t, err)
-
-	err = w.Exec(ctx, meta, root, nil, nil, nil, nil)
-	assert.NoError(t, err)
-
-	rf, err := root.Commit(ctx)
-	assert.NoError(t, err)
-
-	mounts, err = rf.Mount(ctx, false)
-	assert.NoError(t, err)
-
-	lm = snapshot.LocalMounter(mounts)
-
-	target, err = lm.Mount()
-	assert.NoError(t, err)
-
-	dt, err := ioutil.ReadFile(filepath.Join(target, "bar"))
-	assert.NoError(t, err)
-	assert.Equal(t, string(dt), "foo\n")
-
-	lm.Unmount()
-	assert.NoError(t, err)
-
-	err = rf.Release(ctx)
-	assert.NoError(t, err)
-
-	err = snap.Release(ctx)
-	assert.NoError(t, err)
-
-	du2, err := cm.DiskUsage(ctx, client.DiskUsageInfo{})
-	assert.NoError(t, err)
-	assert.Equal(t, 1, len(du2)-len(du))
-
-}
-
-type nopCloser struct {
-	io.Writer
-}
-
-func (n *nopCloser) Close() error {
-	return nil
-}
diff --git a/worker/containerdworker/worker.go b/executor/containerdexecutor/executor.go
similarity index 77%
rename from worker/containerdworker/worker.go
rename to executor/containerdexecutor/executor.go
index 706ce856d7a44..1365ee453951c 100644
--- a/worker/containerdworker/worker.go
+++ b/executor/containerdexecutor/executor.go
@@ -1,4 +1,4 @@
-package containerdworker
+package containerdexecutor
 
 import (
 	"io"
@@ -6,24 +6,24 @@ import (
 	"github.com/containerd/containerd"
 	"github.com/containerd/containerd/cio"
 	"github.com/moby/buildkit/cache"
+	"github.com/moby/buildkit/executor"
+	"github.com/moby/buildkit/executor/oci"
 	"github.com/moby/buildkit/identity"
-	"github.com/moby/buildkit/worker"
-	"github.com/moby/buildkit/worker/oci"
 	"github.com/pkg/errors"
 	"golang.org/x/net/context"
 )
 
-type containerdWorker struct {
+type containerdExecutor struct {
 	client *containerd.Client
 }
 
-func New(client *containerd.Client) worker.Worker {
-	return containerdWorker{
+func New(client *containerd.Client) executor.Executor {
+	return containerdExecutor{
 		client: client,
 	}
 }
 
-func (w containerdWorker) Exec(ctx context.Context, meta worker.Meta, root cache.Mountable, mounts []worker.Mount, stdin io.ReadCloser, stdout, stderr io.WriteCloser) error {
+func (w containerdExecutor) Exec(ctx context.Context, meta executor.Meta, root cache.Mountable, mounts []executor.Mount, stdin io.ReadCloser, stdout, stderr io.WriteCloser) error {
 	id := identity.NewID()
 
 	spec, cleanup, err := oci.GenerateSpec(ctx, meta, mounts, id)
diff --git a/worker/worker.go b/executor/executor.go
similarity index 91%
rename from worker/worker.go
rename to executor/executor.go
index 909a768396592..31c6ba8390374 100644
--- a/worker/worker.go
+++ b/executor/executor.go
@@ -1,4 +1,4 @@
-package worker
+package executor
 
 import (
 	"io"
@@ -23,7 +23,7 @@ type Mount struct {
 	Readonly bool
 }
 
-type Worker interface {
+type Executor interface {
 	// TODO: add stdout/err
 	Exec(ctx context.Context, meta Meta, rootfs cache.Mountable, mounts []Mount, stdin io.ReadCloser, stdout, stderr io.WriteCloser) error
 }
diff --git a/worker/oci/spec_unix.go b/executor/oci/spec_unix.go
similarity index 94%
rename from worker/oci/spec_unix.go
rename to executor/oci/spec_unix.go
index 40e20f7b68402..b3bd791f31aad 100644
--- a/worker/oci/spec_unix.go
+++ b/executor/oci/spec_unix.go
@@ -12,8 +12,8 @@ import (
 	"github.com/containerd/containerd/namespaces"
 	"github.com/containerd/containerd/oci"
 	"github.com/mitchellh/hashstructure"
+	"github.com/moby/buildkit/executor"
 	"github.com/moby/buildkit/snapshot"
-	"github.com/moby/buildkit/worker"
 	specs "github.com/opencontainers/runtime-spec/specs-go"
 	"github.com/pkg/errors"
 )
@@ -21,7 +21,7 @@ import (
 // Ideally we don't have to import whole containerd just for the default spec
 
 // GenerateSpec generates spec using containerd functionality.
-func GenerateSpec(ctx context.Context, meta worker.Meta, mounts []worker.Mount, id string) (*specs.Spec, func(), error) {
+func GenerateSpec(ctx context.Context, meta executor.Meta, mounts []executor.Mount, id string) (*specs.Spec, func(), error) {
 	c := &containers.Container{
 		ID: id,
 	}
diff --git a/worker/runcworker/worker.go b/executor/runcexecutor/executor.go
similarity index 89%
rename from worker/runcworker/worker.go
rename to executor/runcexecutor/executor.go
index 962fb8f0fa3be..ad38214346bb2 100644
--- a/worker/runcworker/worker.go
+++ b/executor/runcexecutor/executor.go
@@ -1,4 +1,4 @@
-package runcworker
+package runcexecutor
 
 import (
 	"encoding/json"
@@ -12,20 +12,20 @@ import (
 	runc "github.com/containerd/go-runc"
 	"github.com/docker/docker/pkg/symlink"
 	"github.com/moby/buildkit/cache"
+	"github.com/moby/buildkit/executor"
+	"github.com/moby/buildkit/executor/oci"
 	"github.com/moby/buildkit/identity"
-	"github.com/moby/buildkit/worker"
-	"github.com/moby/buildkit/worker/oci"
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
 	"golang.org/x/net/context"
 )
 
-type runcworker struct {
+type runcExecutor struct {
 	runc *runc.Runc
 	root string
 }
 
-func New(root string) (worker.Worker, error) {
+func New(root string) (executor.Executor, error) {
 	if err := exec.Command("runc", "--version").Run(); err != nil {
 		return nil, errors.Wrap(err, "failed to find runc binary")
 	}
@@ -47,14 +47,14 @@ func New(root string) (worker.Worker, error) {
 		Setpgid:      true,
 	}
 
-	w := &runcworker{
+	w := &runcExecutor{
 		runc: runtime,
 		root: root,
 	}
 	return w, nil
 }
 
-func (w *runcworker) Exec(ctx context.Context, meta worker.Meta, root cache.Mountable, mounts []worker.Mount, stdin io.ReadCloser, stdout, stderr io.WriteCloser) error {
+func (w *runcExecutor) Exec(ctx context.Context, meta executor.Meta, root cache.Mountable, mounts []executor.Mount, stdin io.ReadCloser, stdout, stderr io.WriteCloser) error {
 
 	rootMount, err := root.Mount(ctx, false)
 	if err != nil {
diff --git a/frontend/dockerfile/dockerfile_test.go b/frontend/dockerfile/dockerfile_test.go
index b0b47d2bbe617..6e3dab3201d34 100644
--- a/frontend/dockerfile/dockerfile_test.go
+++ b/frontend/dockerfile/dockerfile_test.go
@@ -125,7 +125,7 @@ func testDockerfileInvalidCommand(t *testing.T, sb integration.Sandbox) {
 	err = cmd.Run()
 	require.Error(t, err)
 	require.Contains(t, stdout.String(), "/bin/sh -c invalidcmd")
-	require.Contains(t, stdout.String(), "worker failed running")
+	require.Contains(t, stdout.String(), "executor failed running")
 }
 
 func testDockerfileADDFromURL(t *testing.T, sb integration.Sandbox) {
diff --git a/frontend/frontend.go b/frontend/frontend.go
index 29765617d7aa2..60ffa4b18dd55 100644
--- a/frontend/frontend.go
+++ b/frontend/frontend.go
@@ -4,8 +4,8 @@ import (
 	"io"
 
 	"github.com/moby/buildkit/cache"
+	"github.com/moby/buildkit/executor"
 	"github.com/moby/buildkit/solver/pb"
-	"github.com/moby/buildkit/worker"
 	digest "github.com/opencontainers/go-digest"
 	"golang.org/x/net/context"
 )
@@ -17,7 +17,7 @@ type Frontend interface {
 type FrontendLLBBridge interface {
 	Solve(ctx context.Context, req SolveRequest) (cache.ImmutableRef, map[string][]byte, error)
 	ResolveImageConfig(ctx context.Context, ref string) (digest.Digest, []byte, error)
-	Exec(ctx context.Context, meta worker.Meta, rootfs cache.ImmutableRef, stdin io.ReadCloser, stdout, stderr io.WriteCloser) error
+	Exec(ctx context.Context, meta executor.Meta, rootfs cache.ImmutableRef, stdin io.ReadCloser, stdout, stderr io.WriteCloser) error
 }
 
 type SolveRequest struct {
diff --git a/frontend/gateway/gateway.go b/frontend/gateway/gateway.go
index 5b1f877e5ec03..dc38af8d7e14c 100644
--- a/frontend/gateway/gateway.go
+++ b/frontend/gateway/gateway.go
@@ -14,12 +14,12 @@ import (
 	"github.com/docker/distribution/reference"
 	"github.com/moby/buildkit/cache"
 	"github.com/moby/buildkit/client/llb"
+	"github.com/moby/buildkit/executor"
 	"github.com/moby/buildkit/frontend"
 	pb "github.com/moby/buildkit/frontend/gateway/pb"
 	"github.com/moby/buildkit/identity"
 	"github.com/moby/buildkit/session"
 	"github.com/moby/buildkit/snapshot"
-	"github.com/moby/buildkit/worker"
 	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
@@ -144,7 +144,7 @@ func (gf *gatewayFrontend) Solve(ctx context.Context, llbBridge frontend.Fronten
 
 	env = append(env, "BUILDKIT_SESSION_ID="+sid)
 
-	err = llbBridge.Exec(ctx, worker.Meta{
+	err = llbBridge.Exec(ctx, executor.Meta{
 		Env:  env,
 		Args: args,
 		Cwd:  cwd,
diff --git a/hack/dockerfiles/test.Dockerfile b/hack/dockerfiles/test.Dockerfile
index ef35330fb038f..f539a91727a6e 100644
--- a/hack/dockerfiles/test.Dockerfile
+++ b/hack/dockerfiles/test.Dockerfile
@@ -1,6 +1,7 @@
 ARG RUNC_VERSION=74a17296470088de3805e138d3d87c62e613dfc4
 ARG CONTAINERD_VERSION=v1.0.0
-ARG BUILDKIT_TARGET=standalone
+# available targets: buildd(standalone+containerd), buildd-standalone, buildd-containerd
+ARG BUILDKIT_TARGET=buildd
 
 FROM golang:1.9-alpine AS gobuild-base
 RUN apk add --no-cache g++ linux-headers
@@ -44,6 +45,10 @@ FROM buildkit-base AS buildd-containerd
 ENV CGO_ENABLED=0
 RUN go build -ldflags '-d'  -o /usr/bin/buildd-containerd -tags containerd ./cmd/buildd
 
+FROM buildkit-base AS buildd
+ENV CGO_ENABLED=0
+RUN go build -ldflags '-d'  -o /usr/bin/buildd-containerd -tags "standalone containerd" ./cmd/buildd
+
 FROM unit-tests AS integration-tests
 COPY --from=buildctl /usr/bin/buildctl /usr/bin/
 COPY --from=buildd-containerd /usr/bin/buildd-containerd /usr/bin
@@ -65,18 +70,24 @@ RUN apk add --no-cache git
 VOLUME /var/lib/buildkit
 
 # Copy together all binaries needed for standalone mode
-FROM buildkit-export AS buildkit-standalone
+FROM buildkit-export AS buildkit-buildd-standalone
 COPY --from=buildd-standalone /usr/bin/buildd-standalone /usr/bin/
 COPY --from=buildctl /usr/bin/buildctl /usr/bin/
 ENTRYPOINT ["buildd-standalone"]
 
 # Copy together all binaries for containerd mode
-FROM buildkit-export AS buildkit-containerd
+FROM buildkit-export AS buildkit-buildd-containerd
 COPY --from=runc /usr/bin/runc /usr/bin/
 COPY --from=buildd-containerd /usr/bin/buildd-containerd /usr/bin/
 COPY --from=buildctl /usr/bin/buildctl /usr/bin/
 ENTRYPOINT ["buildd-containerd"]
 
+# Copy together all binaries for standalone+containerd mode
+FROM buildkit-export AS buildkit-buildd
+COPY --from=runc /usr/bin/runc /usr/bin/
+COPY --from=buildd /usr/bin/buildd /usr/bin/
+COPY --from=buildctl /usr/bin/buildctl /usr/bin/
+
 FROM alpine AS containerd-runtime
 COPY --from=runc /usr/bin/runc /usr/bin/
 COPY --from=containerd /go/src/github.com/containerd/containerd/bin/containerd* /usr/bin/
diff --git a/metaworker/containerd/containerd.go b/metaworker/containerd/containerd.go
new file mode 100644
index 0000000000000..aeee04356d37b
--- /dev/null
+++ b/metaworker/containerd/containerd.go
@@ -0,0 +1,104 @@
+package containerd
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"time"
+
+	"github.com/containerd/containerd"
+	ctdintrospection "github.com/containerd/containerd/api/services/introspection/v1"
+	"github.com/containerd/containerd/content"
+	ctdplugin "github.com/containerd/containerd/plugin"
+	"github.com/moby/buildkit/cache/metadata"
+	"github.com/moby/buildkit/executor/containerdexecutor"
+	"github.com/moby/buildkit/metaworker"
+	digest "github.com/opencontainers/go-digest"
+	"github.com/pkg/errors"
+	"github.com/sirupsen/logrus"
+)
+
+// TODO(AkihiroSuda): support setting containerd socket timeout
+func NewMetaWorkerOpts(root string, address string) ([]metaworker.MetaWorkerOpt, error) {
+	if err := os.MkdirAll(root, 0700); err != nil {
+		return nil, errors.Wrapf(err, "failed to create %s", root)
+	}
+
+	// TODO: take lock to make sure there are no duplicates
+	client, err := containerd.New(address, containerd.WithDefaultNamespace("buildkit"))
+	if err != nil {
+		return nil, errors.Wrapf(err, "failed to connect client to %q . make sure containerd is running", address)
+	}
+	defaultCtd, err := newContainerd(root, client, containerd.DefaultSnapshotter)
+	if err != nil {
+		return nil, errors.Wrapf(err, "could not load the default containerd snapshotter %s", containerd.DefaultSnapshotter)
+	}
+	opts := []metaworker.MetaWorkerOpt{defaultCtd}
+	ps := client.IntrospectionService()
+	response, err := ps.Plugins(context.TODO(), &ctdintrospection.PluginsRequest{})
+	if err != nil {
+		return nil, err
+	}
+	for _, plugin := range response.Plugins {
+		if plugin.Type == ctdplugin.SnapshotPlugin.String() {
+			if plugin.ID != containerd.DefaultSnapshotter {
+				if plugin.InitErr != nil {
+					logrus.Warnf("ignoring containerd snapshotter %s: %v", plugin.ID, plugin.InitErr)
+					continue
+				}
+				opt, err := newContainerd(root, client, plugin.ID)
+				if err != nil {
+					logrus.Warnf("ignoring containerd snapshotter %s: %v", plugin.ID, err)
+					continue
+				}
+				opts = append(opts, opt)
+			}
+		}
+	}
+	return opts, nil
+}
+
+func newContainerd(root string, client *containerd.Client, snapshotterName string) (metaworker.MetaWorkerOpt, error) {
+	name := "containerd-" + snapshotterName
+	md, err := metadata.NewStore(filepath.Join(root, name+"-metadata.db"))
+	if err != nil {
+		return metaworker.MetaWorkerOpt{}, err
+	}
+	df := client.DiffService()
+	opt := metaworker.MetaWorkerOpt{
+		Name:            name,
+		MetadataStore:   md,
+		Executor:        containerdexecutor.New(client),
+		BaseSnapshotter: client.SnapshotService(snapshotterName),
+		ContentStore:    &noGCContentStore{client.ContentStore()},
+		Applier:         df,
+		Differ:          df,
+		ImageStore:      client.ImageService(),
+	}
+	return opt, nil
+}
+
+// TODO: Replace this with leases
+
+type noGCContentStore struct {
+	content.Store
+}
+type noGCWriter struct {
+	content.Writer
+}
+
+func (cs *noGCContentStore) Writer(ctx context.Context, ref string, size int64, expected digest.Digest) (content.Writer, error) {
+	w, err := cs.Store.Writer(ctx, ref, size, expected)
+	return &noGCWriter{w}, err
+}
+
+func (w *noGCWriter) Commit(ctx context.Context, size int64, expected digest.Digest, opts ...content.Opt) error {
+	opts = append(opts, func(info *content.Info) error {
+		if info.Labels == nil {
+			info.Labels = map[string]string{}
+		}
+		info.Labels["containerd.io/gc.root"] = time.Now().UTC().Format(time.RFC3339Nano)
+		return nil
+	})
+	return w.Writer.Commit(ctx, size, expected, opts...)
+}
diff --git a/control/control_default.go b/metaworker/metaworker.go
similarity index 52%
rename from control/control_default.go
rename to metaworker/metaworker.go
index cee931a667c0a..2340a8ddf7c7d 100644
--- a/control/control_default.go
+++ b/metaworker/metaworker.go
@@ -1,9 +1,7 @@
-// +build standalone containerd
-
-package control
+package metaworker
 
 import (
-	"path/filepath"
+	"golang.org/x/net/context"
 
 	"github.com/containerd/containerd/content"
 	"github.com/containerd/containerd/diff"
@@ -14,12 +12,10 @@ import (
 	"github.com/moby/buildkit/cache/instructioncache"
 	"github.com/moby/buildkit/cache/metadata"
 	"github.com/moby/buildkit/client"
+	"github.com/moby/buildkit/executor"
 	"github.com/moby/buildkit/exporter"
 	imageexporter "github.com/moby/buildkit/exporter/containerimage"
 	localexporter "github.com/moby/buildkit/exporter/local"
-	"github.com/moby/buildkit/frontend"
-	"github.com/moby/buildkit/frontend/dockerfile"
-	"github.com/moby/buildkit/frontend/gateway"
 	"github.com/moby/buildkit/session"
 	"github.com/moby/buildkit/snapshot/blobmapping"
 	"github.com/moby/buildkit/source"
@@ -27,41 +23,64 @@ import (
 	"github.com/moby/buildkit/source/git"
 	"github.com/moby/buildkit/source/http"
 	"github.com/moby/buildkit/source/local"
+	digest "github.com/opencontainers/go-digest"
 )
 
-type pullDeps struct {
-	Snapshotter  ctdsnapshot.Snapshotter
-	ContentStore content.Store
-	Applier      diff.Differ
-	Differ       diff.Differ
-	Images       images.Store
+// MetaWorkerOpt is a constructor for MetaWorker
+type MetaWorkerOpt struct {
+	Name            string
+	MetadataStore   *metadata.Store
+	Executor        executor.Executor
+	BaseSnapshotter ctdsnapshot.Snapshotter
+	ContentStore    content.Store
+	Applier         diff.Differ
+	Differ          diff.Differ
+	ImageStore      images.Store
 }
 
-func defaultControllerOpts(root string, pd pullDeps) (*Opt, error) {
-	md, err := metadata.NewStore(filepath.Join(root, "metadata.db"))
-	if err != nil {
-		return nil, err
-	}
+// MetaWorker is a worker instance with dedicated snapshotter, cache, and so on.
+type MetaWorker struct {
+	MetaWorkerOpt
+	Snapshotter      ctdsnapshot.Snapshotter // blobmapping snapshotter
+	CacheManager     cache.Manager
+	SourceManager    *source.Manager
+	InstructionCache InstructionCache
+	Exporters        map[string]exporter.Exporter
+	SessionManager   *session.Manager
+	ImageSource      source.Source
+	CacheExporter    *cacheimport.CacheExporter
+	CacheImporter    *cacheimport.CacheImporter
+	// no frontend
+}
+
+type InstructionCache interface {
+	Probe(ctx context.Context, key digest.Digest) (bool, error)
+	Lookup(ctx context.Context, key digest.Digest, msg string) (interface{}, error) // TODO: regular ref
+	Set(key digest.Digest, ref interface{}) error
+	SetContentMapping(contentKey, key digest.Digest) error
+	GetContentMapping(dgst digest.Digest) ([]digest.Digest, error)
+}
 
-	snapshotter, err := blobmapping.NewSnapshotter(blobmapping.Opt{
-		Content:       pd.ContentStore,
-		Snapshotter:   pd.Snapshotter,
-		MetadataStore: md,
+func NewMetaWorker(opt MetaWorkerOpt) (*MetaWorker, error) {
+	bmSnapshotter, err := blobmapping.NewSnapshotter(blobmapping.Opt{
+		Content:       opt.ContentStore,
+		Snapshotter:   opt.BaseSnapshotter,
+		MetadataStore: opt.MetadataStore,
 	})
 	if err != nil {
 		return nil, err
 	}
 
 	cm, err := cache.NewManager(cache.ManagerOpt{
-		Snapshotter:   snapshotter,
-		MetadataStore: md,
+		Snapshotter:   bmSnapshotter,
+		MetadataStore: opt.MetadataStore,
 	})
 	if err != nil {
 		return nil, err
 	}
 
 	ic := &instructioncache.LocalStore{
-		MetadataStore: md,
+		MetadataStore: opt.MetadataStore,
 		Cache:         cm,
 	}
 
@@ -76,10 +95,10 @@ func defaultControllerOpts(root string, pd pullDeps) (*Opt, error) {
 	}
 
 	is, err := containerimage.NewSource(containerimage.SourceOpt{
-		Snapshotter:    snapshotter,
-		ContentStore:   pd.ContentStore,
+		Snapshotter:    bmSnapshotter,
+		ContentStore:   opt.ContentStore,
 		SessionManager: sessm,
-		Applier:        pd.Applier,
+		Applier:        opt.Applier,
 		CacheAccessor:  cm,
 	})
 	if err != nil {
@@ -90,7 +109,7 @@ func defaultControllerOpts(root string, pd pullDeps) (*Opt, error) {
 
 	gs, err := git.NewSource(git.Opt{
 		CacheAccessor: cm,
-		MetadataStore: md,
+		MetadataStore: opt.MetadataStore,
 	})
 	if err != nil {
 		return nil, err
@@ -100,7 +119,7 @@ func defaultControllerOpts(root string, pd pullDeps) (*Opt, error) {
 
 	hs, err := http.NewSource(http.Opt{
 		CacheAccessor: cm,
-		MetadataStore: md,
+		MetadataStore: opt.MetadataStore,
 	})
 	if err != nil {
 		return nil, err
@@ -111,7 +130,7 @@ func defaultControllerOpts(root string, pd pullDeps) (*Opt, error) {
 	ss, err := local.NewSource(local.Opt{
 		SessionManager: sessm,
 		CacheAccessor:  cm,
-		MetadataStore:  md,
+		MetadataStore:  opt.MetadataStore,
 	})
 	if err != nil {
 		return nil, err
@@ -121,10 +140,10 @@ func defaultControllerOpts(root string, pd pullDeps) (*Opt, error) {
 	exporters := map[string]exporter.Exporter{}
 
 	imageExporter, err := imageexporter.New(imageexporter.Opt{
-		Snapshotter:    snapshotter,
-		ContentStore:   pd.ContentStore,
-		Differ:         pd.Differ,
-		Images:         pd.Images,
+		Snapshotter:    bmSnapshotter,
+		ContentStore:   opt.ContentStore,
+		Differ:         opt.Differ,
+		Images:         opt.ImageStore,
 		SessionManager: sessm,
 	})
 	if err != nil {
@@ -140,33 +159,29 @@ func defaultControllerOpts(root string, pd pullDeps) (*Opt, error) {
 	}
 	exporters[client.ExporterLocal] = localExporter
 
-	frontends := map[string]frontend.Frontend{}
-	frontends["dockerfile.v0"] = dockerfile.NewDockerfileFrontend()
-	frontends["gateway.v0"] = gateway.NewGatewayFrontend()
-
 	ce := cacheimport.NewCacheExporter(cacheimport.ExporterOpt{
-		Snapshotter:    snapshotter,
-		ContentStore:   pd.ContentStore,
+		Snapshotter:    bmSnapshotter,
+		ContentStore:   opt.ContentStore,
 		SessionManager: sessm,
-		Differ:         pd.Differ,
+		Differ:         opt.Differ,
 	})
 
 	ci := cacheimport.NewCacheImporter(cacheimport.ImportOpt{
-		Snapshotter:    snapshotter,
-		ContentStore:   pd.ContentStore,
-		Applier:        pd.Applier,
+		Snapshotter:    bmSnapshotter,
+		ContentStore:   opt.ContentStore,
+		Applier:        opt.Applier,
 		CacheAccessor:  cm,
 		SessionManager: sessm,
 	})
 
-	return &Opt{
-		Snapshotter:      snapshotter,
+	return &MetaWorker{
+		MetaWorkerOpt:    opt,
+		Snapshotter:      bmSnapshotter,
 		CacheManager:     cm,
 		SourceManager:    sm,
 		InstructionCache: ic,
 		Exporters:        exporters,
 		SessionManager:   sessm,
-		Frontends:        frontends,
 		ImageSource:      is,
 		CacheExporter:    ce,
 		CacheImporter:    ci,
diff --git a/control/control_standalone.go b/metaworker/runc/runc.go
similarity index 79%
rename from control/control_standalone.go
rename to metaworker/runc/runc.go
index ea5983d94639a..95f11ccb9f02a 100644
--- a/control/control_standalone.go
+++ b/metaworker/runc/runc.go
@@ -1,6 +1,4 @@
-// +build standalone
-
-package control
+package runc
 
 import (
 	"context"
@@ -11,81 +9,85 @@ import (
 	"github.com/containerd/containerd/content"
 	"github.com/containerd/containerd/content/local"
 	"github.com/containerd/containerd/diff/walking"
-	"github.com/containerd/containerd/metadata"
+	ctdmetadata "github.com/containerd/containerd/metadata"
 	"github.com/containerd/containerd/mount"
 	"github.com/containerd/containerd/namespaces"
 	ctdsnapshot "github.com/containerd/containerd/snapshots"
 	"github.com/containerd/containerd/snapshots/overlay"
-	"github.com/moby/buildkit/worker/runcworker"
-	digest "github.com/opencontainers/go-digest"
+	"github.com/moby/buildkit/cache/metadata"
+	"github.com/moby/buildkit/executor/runcexecutor"
+	"github.com/moby/buildkit/metaworker"
+	"github.com/opencontainers/go-digest"
 	"github.com/pkg/errors"
 )
 
-func NewStandalone(root string) (*Controller, error) {
+func NewMetaWorkerOpts(root string) ([]metaworker.MetaWorkerOpt, error) {
 	if err := os.MkdirAll(root, 0700); err != nil {
 		return nil, errors.Wrapf(err, "failed to create %s", root)
 	}
-
-	// TODO: take lock to make sure there are no duplicates
-
-	pd, err := newStandalonePullDeps(root)
+	runcOverlay, err := newRuncOverlay(root)
 	if err != nil {
 		return nil, err
 	}
+	return []metaworker.MetaWorkerOpt{runcOverlay}, nil
+}
 
-	opt, err := defaultControllerOpts(root, *pd)
+func newRuncOverlay(root string) (metaworker.MetaWorkerOpt, error) {
+	var opt metaworker.MetaWorkerOpt
+	name := "runc-overlay"
+	root = filepath.Join(root, name)
+	if err := os.MkdirAll(root, 0700); err != nil {
+		return opt, err
+	}
+	md, err := metadata.NewStore(filepath.Join(root, name+"-metadata.db"))
 	if err != nil {
-		return nil, err
+		return opt, err
 	}
-
-	w, err := runcworker.New(filepath.Join(root, "runc"))
+	exe, err := runcexecutor.New(filepath.Join(root, "executor"))
 	if err != nil {
-		return nil, err
+		return opt, err
 	}
-
-	opt.Worker = w
-
-	return NewController(*opt)
-}
-
-func newStandalonePullDeps(root string) (*pullDeps, error) {
 	s, err := overlay.NewSnapshotter(filepath.Join(root, "snapshots"))
 	if err != nil {
-		return nil, err
+		return opt, err
 	}
 
 	c, err := local.NewStore(filepath.Join(root, "content"))
 	if err != nil {
-		return nil, err
+		return opt, err
 	}
 
 	db, err := bolt.Open(filepath.Join(root, "containerdmeta.db"), 0644, nil)
 	if err != nil {
-		return nil, err
+		return opt, err
 	}
 
-	mdb := metadata.NewDB(db, c, map[string]ctdsnapshot.Snapshotter{
+	mdb := ctdmetadata.NewDB(db, c, map[string]ctdsnapshot.Snapshotter{
 		"overlay": s,
 	})
 	if err := mdb.Init(context.TODO()); err != nil {
-		return nil, err
+		return opt, err
 	}
 
 	c = &nsContent{mdb.ContentStore()}
-
 	df, err := walking.NewWalkingDiff(c)
 	if err != nil {
-		return nil, err
+		return opt, err
 	}
 
 	// TODO: call mdb.GarbageCollect . maybe just inject it into nsSnapshotter.Remove and csContent.Delete
 
-	return &pullDeps{
-		Snapshotter:  &nsSnapshotter{mdb.Snapshotter("overlay")},
-		ContentStore: c,
-		Applier:      df,
-		Differ:       df,
-	}, nil
+	opt = metaworker.MetaWorkerOpt{
+		Name:            name,
+		MetadataStore:   md,
+		Executor:        exe,
+		BaseSnapshotter: &nsSnapshotter{mdb.Snapshotter("overlay")},
+		ContentStore:    c,
+		Applier:         df,
+		Differ:          df,
+		ImageStore:      nil, // explicitly
+	}
+	return opt, nil
 }
 
 // this should be supported by containerd. currently packages are unusable without wrapping
diff --git a/solver/exec.go b/solver/exec.go
index 7b460013c2bfe..9788ca5692203 100644
--- a/solver/exec.go
+++ b/solver/exec.go
@@ -9,9 +9,9 @@ import (
 	"strings"
 
 	"github.com/moby/buildkit/cache"
+	"github.com/moby/buildkit/executor"
 	"github.com/moby/buildkit/solver/pb"
 	"github.com/moby/buildkit/util/progress/logs"
-	"github.com/moby/buildkit/worker"
 	digest "github.com/opencontainers/go-digest"
 	"github.com/pkg/errors"
 	"golang.org/x/net/context"
@@ -22,15 +22,15 @@ const execCacheType = "buildkit.exec.v0"
 type execOp struct {
 	op        *pb.ExecOp
 	cm        cache.Manager
-	w         worker.Worker
+	exe       executor.Executor
 	numInputs int
 }
 
-func newExecOp(v Vertex, op *pb.Op_Exec, cm cache.Manager, w worker.Worker) (Op, error) {
+func newExecOp(v Vertex, op *pb.Op_Exec, cm cache.Manager, exe executor.Executor) (Op, error) {
 	return &execOp{
 		op:        op.Exec,
 		cm:        cm,
-		w:         w,
+		exe:       exe,
 		numInputs: len(v.Inputs()),
 	}, nil
 }
@@ -55,7 +55,7 @@ func (e *execOp) CacheKey(ctx context.Context) (digest.Digest, error) {
 }
 
 func (e *execOp) Run(ctx context.Context, inputs []Reference) ([]Reference, error) {
-	var mounts []worker.Mount
+	var mounts []executor.Mount
 	var outputs []Reference
 	var root cache.Mountable
 
@@ -97,7 +97,7 @@ func (e *execOp) Run(ctx context.Context, inputs []Reference) ([]Reference, erro
 		if m.Dest == pb.RootMount {
 			root = mountable
 		} else {
-			mounts = append(mounts, worker.Mount{Src: mountable, Dest: m.Dest, Readonly: m.Readonly, Selector: m.Selector})
+			mounts = append(mounts, executor.Mount{Src: mountable, Dest: m.Dest, Readonly: m.Readonly, Selector: m.Selector})
 		}
 	}
 
@@ -105,7 +105,7 @@ func (e *execOp) Run(ctx context.Context, inputs []Reference) ([]Reference, erro
 		return mounts[i].Dest < mounts[j].Dest
 	})
 
-	meta := worker.Meta{
+	meta := executor.Meta{
 		Args: e.op.Meta.Args,
 		Env:  e.op.Meta.Env,
 		Cwd:  e.op.Meta.Cwd,
@@ -115,8 +115,8 @@ func (e *execOp) Run(ctx context.Context, inputs []Reference) ([]Reference, erro
 	defer stdout.Close()
 	defer stderr.Close()
 
-	if err := e.w.Exec(ctx, meta, root, mounts, nil, stdout, stderr); err != nil {
-		return nil, errors.Wrapf(err, "worker failed running %v", meta.Args)
+	if err := e.exe.Exec(ctx, meta, root, mounts, nil, stdout, stderr); err != nil {
+		return nil, errors.Wrapf(err, "executor failed running %v", meta.Args)
 	}
 
 	refs := []Reference{}
diff --git a/solver/pb/ops.pb.go b/solver/pb/ops.pb.go
index ca236d4fa16cb..b8bf1b26ac7f2 100644
--- a/solver/pb/ops.pb.go
+++ b/solver/pb/ops.pb.go
@@ -19,6 +19,7 @@
 		BuildOp
 		BuildInput
 		OpMetadata
+		WorkerConstraint
 		Definition
 */
 package pb
@@ -451,6 +452,8 @@ type OpMetadata struct {
 	IgnoreCache bool `protobuf:"varint,1,opt,name=ignore_cache,json=ignoreCache,proto3" json:"ignore_cache,omitempty"`
 	// Description can be used for keeping any text fields that builder doesn't parse
 	Description map[string]string `protobuf:"bytes,2,rep,name=description" json:"description,omitempty" protobuf_key:"bytes,1,opt,name=key,proto3" protobuf_val:"bytes,2,opt,name=value,proto3"`
+	// TODO: add worker constraint, etc.
+	WorkerConstraint *WorkerConstraint `protobuf:"bytes,3,opt,name=worker_constraint,json=workerConstraint" json:"worker_constraint,omitempty"`
 }
 
 func (m *OpMetadata) Reset()                    { *m = OpMetadata{} }
@@ -472,6 +475,30 @@ func (m *OpMetadata) GetDescription() map[string]string {
 	return nil
 }
 
+func (m *OpMetadata) GetWorkerConstraint() *WorkerConstraint {
+	if m != nil {
+		return m.WorkerConstraint
+	}
+	return nil
+}
+
+// WorkerConstraint is WIP. Will be changed.
+type WorkerConstraint struct {
+	WorkerName string `protobuf:"bytes,1,opt,name=worker_name,json=workerName,proto3" json:"worker_name,omitempty"`
+}
+
+func (m *WorkerConstraint) Reset()                    { *m = WorkerConstraint{} }
+func (m *WorkerConstraint) String() string            { return proto.CompactTextString(m) }
+func (*WorkerConstraint) ProtoMessage()               {}
+func (*WorkerConstraint) Descriptor() ([]byte, []int) { return fileDescriptorOps, []int{11} }
+
+func (m *WorkerConstraint) GetWorkerName() string {
+	if m != nil {
+		return m.WorkerName
+	}
+	return ""
+}
+
 // Definition is the LLB definition structure with per-vertex metadata entries
 type Definition struct {
 	Def [][]byte `protobuf:"bytes,1,rep,name=def" json:"def,omitempty"`
@@ -482,7 +509,7 @@ type Definition struct {
 func (m *Definition) Reset()                    { *m = Definition{} }
 func (m *Definition) String() string            { return proto.CompactTextString(m) }
 func (*Definition) ProtoMessage()               {}
-func (*Definition) Descriptor() ([]byte, []int) { return fileDescriptorOps, []int{11} }
+func (*Definition) Descriptor() ([]byte, []int) { return fileDescriptorOps, []int{12} }
 
 func (m *Definition) GetDef() [][]byte {
 	if m != nil {
@@ -510,6 +537,7 @@ func init() {
 	proto.RegisterType((*BuildOp)(nil), "pb.BuildOp")
 	proto.RegisterType((*BuildInput)(nil), "pb.BuildInput")
 	proto.RegisterType((*OpMetadata)(nil), "pb.OpMetadata")
+	proto.RegisterType((*WorkerConstraint)(nil), "pb.WorkerConstraint")
 	proto.RegisterType((*Definition)(nil), "pb.Definition")
 }
 func (m *Op) Marshal() (dAtA []byte, err error) {
@@ -1027,6 +1055,40 @@ func (m *OpMetadata) MarshalTo(dAtA []byte) (int, error) {
 			i += copy(dAtA[i:], v)
 		}
 	}
+	if m.WorkerConstraint != nil {
+		dAtA[i] = 0x1a
+		i++
+		i = encodeVarintOps(dAtA, i, uint64(m.WorkerConstraint.Size()))
+		n9, err := m.WorkerConstraint.MarshalTo(dAtA[i:])
+		if err != nil {
+			return 0, err
+		}
+		i += n9
+	}
+	return i, nil
+}
+
+func (m *WorkerConstraint) Marshal() (dAtA []byte, err error) {
+	size := m.Size()
+	dAtA = make([]byte, size)
+	n, err := m.MarshalTo(dAtA)
+	if err != nil {
+		return nil, err
+	}
+	return dAtA[:n], nil
+}
+
+func (m *WorkerConstraint) MarshalTo(dAtA []byte) (int, error) {
+	var i int
+	_ = i
+	var l int
+	_ = l
+	if len(m.WorkerName) > 0 {
+		dAtA[i] = 0xa
+		i++
+		i = encodeVarintOps(dAtA, i, uint64(len(m.WorkerName)))
+		i += copy(dAtA[i:], m.WorkerName)
+	}
 	return i, nil
 }
 
@@ -1072,11 +1134,11 @@ func (m *Definition) MarshalTo(dAtA []byte) (int, error) {
 			dAtA[i] = 0x12
 			i++
 			i = encodeVarintOps(dAtA, i, uint64((&v).Size()))
-			n9, err := (&v).MarshalTo(dAtA[i:])
+			n10, err := (&v).MarshalTo(dAtA[i:])
 			if err != nil {
 				return 0, err
 			}
-			i += n9
+			i += n10
 		}
 	}
 	return i, nil
@@ -1338,6 +1400,20 @@ func (m *OpMetadata) Size() (n int) {
 			n += mapEntrySize + 1 + sovOps(uint64(mapEntrySize))
 		}
 	}
+	if m.WorkerConstraint != nil {
+		l = m.WorkerConstraint.Size()
+		n += 1 + l + sovOps(uint64(l))
+	}
+	return n
+}
+
+func (m *WorkerConstraint) Size() (n int) {
+	var l int
+	_ = l
+	l = len(m.WorkerName)
+	if l > 0 {
+		n += 1 + l + sovOps(uint64(l))
+	}
 	return n
 }
 
@@ -3075,6 +3151,118 @@ func (m *OpMetadata) Unmarshal(dAtA []byte) error {
 				m.Description[mapkey] = mapvalue
 			}
 			iNdEx = postIndex
+		case 3:
+			if wireType != 2 {
+				return fmt.Errorf("proto: wrong wireType = %d for field WorkerConstraint", wireType)
+			}
+			var msglen int
+			for shift := uint(0); ; shift += 7 {
+				if shift >= 64 {
+					return ErrIntOverflowOps
+				}
+				if iNdEx >= l {
+					return io.ErrUnexpectedEOF
+				}
+				b := dAtA[iNdEx]
+				iNdEx++
+				msglen |= (int(b) & 0x7F) << shift
+				if b < 0x80 {
+					break
+				}
+			}
+			if msglen < 0 {
+				return ErrInvalidLengthOps
+			}
+			postIndex := iNdEx + msglen
+			if postIndex > l {
+				return io.ErrUnexpectedEOF
+			}
+			if m.WorkerConstraint == nil {
+				m.WorkerConstraint = &WorkerConstraint{}
+			}
+			if err := m.WorkerConstraint.Unmarshal(dAtA[iNdEx:postIndex]); err != nil {
+				return err
+			}
+			iNdEx = postIndex
+		default:
+			iNdEx = preIndex
+			skippy, err := skipOps(dAtA[iNdEx:])
+			if err != nil {
+				return err
+			}
+			if skippy < 0 {
+				return ErrInvalidLengthOps
+			}
+			if (iNdEx + skippy) > l {
+				return io.ErrUnexpectedEOF
+			}
+			iNdEx += skippy
+		}
+	}
+
+	if iNdEx > l {
+		return io.ErrUnexpectedEOF
+	}
+	return nil
+}
+func (m *WorkerConstraint) Unmarshal(dAtA []byte) error {
+	l := len(dAtA)
+	iNdEx := 0
+	for iNdEx < l {
+		preIndex := iNdEx
+		var wire uint64
+		for shift := uint(0); ; shift += 7 {
+			if shift >= 64 {
+				return ErrIntOverflowOps
+			}
+			if iNdEx >= l {
+				return io.ErrUnexpectedEOF
+			}
+			b := dAtA[iNdEx]
+			iNdEx++
+			wire |= (uint64(b) & 0x7F) << shift
+			if b < 0x80 {
+				break
+			}
+		}
+		fieldNum := int32(wire >> 3)
+		wireType := int(wire & 0x7)
+		if wireType == 4 {
+			return fmt.Errorf("proto: WorkerConstraint: wiretype end group for non-group")
+		}
+		if fieldNum <= 0 {
+			return fmt.Errorf("proto: WorkerConstraint: illegal tag %d (wire type %d)", fieldNum, wire)
+		}
+		switch fieldNum {
+		case 1:
+			if wireType != 2 {
+				return fmt.Errorf("proto: wrong wireType = %d for field WorkerName", wireType)
+			}
+			var stringLen uint64
+			for shift := uint(0); ; shift += 7 {
+				if shift >= 64 {
+					return ErrIntOverflowOps
+				}
+				if iNdEx >= l {
+					return io.ErrUnexpectedEOF
+				}
+				b := dAtA[iNdEx]
+				iNdEx++
+				stringLen |= (uint64(b) & 0x7F) << shift
+				if b < 0x80 {
+					break
+				}
+			}
+			intStringLen := int(stringLen)
+			if intStringLen < 0 {
+				return ErrInvalidLengthOps
+			}
+			postIndex := iNdEx + intStringLen
+			if postIndex > l {
+				return io.ErrUnexpectedEOF
+			}
+			m.WorkerName = string(dAtA[iNdEx:postIndex])
+			iNdEx = postIndex
 		default:
 			iNdEx = preIndex
 			skippy, err := skipOps(dAtA[iNdEx:])
@@ -3404,54 +3592,58 @@ var (
 func init() { proto.RegisterFile("ops.proto", fileDescriptorOps) }
 
 var fileDescriptorOps = []byte{
-	// 783 bytes of a gzipped FileDescriptorProto
-	0x1f, 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02, 0xff, 0xac, 0x55, 0xcd, 0x6e, 0xdb, 0x46,
-	0x10, 0x36, 0xa9, 0x1f, 0x4b, 0x43, 0xb7, 0x30, 0xb6, 0x45, 0x2b, 0x08, 0x86, 0xac, 0xb2, 0x45,
-	0xa1, 0xb6, 0x36, 0x05, 0xa8, 0x40, 0x61, 0xf4, 0x60, 0xc0, 0xb2, 0x0d, 0x54, 0x2d, 0x0c, 0x01,
-	0xdb, 0x07, 0x28, 0x28, 0x72, 0x25, 0x13, 0x95, 0xb8, 0x04, 0xb9, 0x74, 0xad, 0x4b, 0x0f, 0x7d,
-	0x82, 0x02, 0x79, 0x8b, 0x1c, 0x73, 0x4f, 0xce, 0x3e, 0xe6, 0x9a, 0x1c, 0x9c, 0xc0, 0x79, 0x91,
-	0x60, 0x66, 0x57, 0x22, 0x9d, 0x38, 0x80, 0x8d, 0xe4, 0xa4, 0xdd, 0x99, 0x6f, 0xbf, 0xfd, 0xe6,
-	0x9b, 0x59, 0x0a, 0x9a, 0x32, 0xc9, 0xbc, 0x24, 0x95, 0x4a, 0x32, 0x3b, 0x99, 0xb4, 0xf7, 0x67,
-	0x91, 0x3a, 0xcf, 0x27, 0x5e, 0x20, 0x17, 0xfd, 0x99, 0x9c, 0xc9, 0x3e, 0xa5, 0x26, 0xf9, 0x94,
-	0x76, 0xb4, 0xa1, 0x95, 0x3e, 0xe2, 0x3e, 0xb3, 0xc0, 0x1e, 0x27, 0xec, 0x1b, 0xa8, 0x47, 0x71,
-	0x92, 0xab, 0xac, 0x65, 0x75, 0x2b, 0x3d, 0x67, 0xd0, 0xf4, 0x92, 0x89, 0x37, 0xc2, 0x08, 0x37,
-	0x09, 0xd6, 0x85, 0xaa, 0xb8, 0x14, 0x41, 0xcb, 0xee, 0x5a, 0x3d, 0x67, 0x00, 0x08, 0x38, 0xbd,
-	0x14, 0xc1, 0x38, 0xf9, 0x6d, 0x83, 0x53, 0x86, 0x7d, 0x0f, 0xf5, 0x4c, 0xe6, 0x69, 0x20, 0x5a,
-	0x15, 0xc2, 0x6c, 0x21, 0xe6, 0x4f, 0x8a, 0x10, 0xca, 0x64, 0x91, 0x29, 0x90, 0xc9, 0xb2, 0x55,
-	0x2d, 0x98, 0x8e, 0x65, 0xb2, 0xd4, 0x4c, 0x98, 0x61, 0xdf, 0x42, 0x6d, 0x92, 0x47, 0xf3, 0xb0,
-	0x55, 0x23, 0x88, 0x83, 0x90, 0x21, 0x06, 0x08, 0xa3, 0x73, 0xc3, 0x2a, 0xd8, 0x32, 0x71, 0xff,
-	0x85, 0x1a, 0xe9, 0x64, 0xbf, 0x43, 0x3d, 0x8c, 0x66, 0x22, 0x53, 0x2d, 0xab, 0x6b, 0xf5, 0x9a,
-	0xc3, 0xc1, 0xd5, 0xf5, 0xee, 0xc6, 0xcb, 0xeb, 0xdd, 0x1f, 0x4b, 0x86, 0xc8, 0x44, 0xc4, 0x81,
-	0x8c, 0x95, 0x1f, 0xc5, 0x22, 0xcd, 0xfa, 0x33, 0xb9, 0xaf, 0x8f, 0x78, 0x27, 0xf4, 0xc3, 0x0d,
-	0x03, 0xfb, 0x01, 0x6a, 0x51, 0x1c, 0x8a, 0x4b, 0x2a, 0xb6, 0x32, 0xfc, 0xc2, 0x50, 0x39, 0xe3,
-	0x5c, 0x25, 0xb9, 0x1a, 0x61, 0x8a, 0x6b, 0x84, 0x3b, 0x82, 0xba, 0xb6, 0x81, 0xed, 0x40, 0x75,
-	0x21, 0x94, 0x4f, 0xd7, 0x3b, 0x83, 0x06, 0x6a, 0x3e, 0x13, 0xca, 0xe7, 0x14, 0x45, 0x87, 0x17,
-	0x32, 0x8f, 0x55, 0xd6, 0xb2, 0x0b, 0x87, 0xcf, 0x30, 0xc2, 0x4d, 0xc2, 0x3d, 0x84, 0x2a, 0x1e,
-	0x60, 0x0c, 0xaa, 0x7e, 0x3a, 0xd3, 0xad, 0x68, 0x72, 0x5a, 0xb3, 0x6d, 0xa8, 0x88, 0xf8, 0x82,
-	0xce, 0x36, 0x39, 0x2e, 0x31, 0x12, 0xfc, 0x13, 0x92, 0xd5, 0x4d, 0x8e, 0x4b, 0xf7, 0xb1, 0x05,
-	0x35, 0x62, 0x64, 0x3d, 0xd4, 0x9f, 0xe4, 0xda, 0x8a, 0xca, 0x90, 0x19, 0xfd, 0x40, 0x4e, 0xad,
-	0xe5, 0xa3, 0x6b, 0x6d, 0x68, 0x64, 0x62, 0x2e, 0x02, 0x25, 0x53, 0x2a, 0xb6, 0xc9, 0xd7, 0x7b,
-	0xd4, 0x11, 0xa2, 0x9f, 0xfa, 0x0a, 0x5a, 0xb3, 0x9f, 0xa0, 0x2e, 0xc9, 0x04, 0xea, 0xde, 0x07,
-	0xac, 0x31, 0x10, 0x24, 0x4f, 0x85, 0x1f, 0xca, 0x78, 0xbe, 0xa4, 0x4e, 0x36, 0xf8, 0x7a, 0xef,
-	0x1e, 0x42, 0x5d, 0x37, 0x9d, 0x75, 0xa1, 0x92, 0xa5, 0x81, 0x19, 0xbc, 0xcf, 0x57, 0xd3, 0xa0,
-	0xe7, 0x86, 0x63, 0x6a, 0x2d, 0xc4, 0x2e, 0x84, 0xb8, 0x1c, 0xa0, 0x80, 0x7d, 0x9a, 0x82, 0xdd,
-	0x47, 0x16, 0x34, 0x56, 0xf3, 0xca, 0x3a, 0x00, 0x51, 0x28, 0x62, 0x15, 0x4d, 0x23, 0x91, 0xea,
-	0x99, 0xe2, 0xa5, 0x08, 0xdb, 0x87, 0x9a, 0xaf, 0x54, 0xba, 0xea, 0xe7, 0xd7, 0xe5, 0x61, 0xf7,
-	0x8e, 0x30, 0x73, 0x1a, 0xab, 0x74, 0xc9, 0x35, 0xaa, 0x7d, 0x00, 0x50, 0x04, 0xb1, 0x79, 0x7f,
-	0x8b, 0xa5, 0x61, 0xc5, 0x25, 0xfb, 0x12, 0x6a, 0x17, 0xfe, 0x3c, 0x17, 0x46, 0x94, 0xde, 0xfc,
-	0x6a, 0x1f, 0x58, 0xee, 0x53, 0x1b, 0x36, 0xcd, 0xf0, 0xb3, 0x3d, 0xd8, 0xa4, 0xe1, 0x37, 0x8a,
-	0xee, 0xae, 0x74, 0x05, 0x61, 0xfd, 0xf5, 0xab, 0x2e, 0x69, 0x34, 0x54, 0xfa, 0x75, 0x1b, 0x8d,
-	0xc5, 0x1b, 0xaf, 0x84, 0x62, 0x6a, 0x9e, 0x2f, 0xb5, 0xe2, 0x44, 0x4c, 0xa3, 0x38, 0x52, 0x91,
-	0x8c, 0x39, 0xa6, 0xd8, 0xde, 0xaa, 0xea, 0x2a, 0x31, 0x7e, 0x55, 0x66, 0x7c, 0xbf, 0xe8, 0x11,
-	0x38, 0xa5, 0x6b, 0xee, 0xa8, 0xfa, 0xbb, 0x72, 0xd5, 0xe6, 0x4a, 0xa2, 0xd3, 0xdf, 0x9e, 0xc2,
-	0x85, 0x8f, 0xf0, 0xef, 0x17, 0x80, 0x82, 0xf2, 0xfe, 0x93, 0xe2, 0x3e, 0xb1, 0x00, 0xc6, 0x09,
-	0xbe, 0xc8, 0xd0, 0xa7, 0x07, 0xbc, 0x15, 0xcd, 0x62, 0x99, 0x8a, 0xbf, 0x02, 0x3f, 0x38, 0x17,
-	0x74, 0xbe, 0xc1, 0x1d, 0x1d, 0x3b, 0xc6, 0x10, 0x3b, 0x02, 0x27, 0x14, 0x59, 0x90, 0x46, 0x09,
-	0x1a, 0x66, 0x4c, 0xdf, 0xc5, 0x9a, 0x0a, 0x1e, 0xef, 0xa4, 0x40, 0x68, 0xaf, 0xca, 0x67, 0xda,
-	0x87, 0xb0, 0xfd, 0x2e, 0xe0, 0x41, 0xc5, 0xbe, 0xb0, 0x00, 0x8a, 0x9e, 0xe1, 0x51, 0x6c, 0x28,
-	0xbe, 0xad, 0x2d, 0xdd, 0xc0, 0x39, 0x34, 0x16, 0x46, 0x8a, 0x11, 0xb8, 0x73, 0xbb, 0xcf, 0xde,
-	0x4a, 0x29, 0x5d, 0xae, 0x3f, 0xa3, 0xff, 0xbd, 0x7a, 0xd0, 0x67, 0x74, 0x7d, 0x43, 0xfb, 0x0f,
-	0xf8, 0xec, 0x16, 0xdd, 0x3d, 0x47, 0xa0, 0xb0, 0xab, 0x54, 0xdb, 0x70, 0xfb, 0xea, 0xa6, 0x63,
-	0x3d, 0xbf, 0xe9, 0x58, 0xaf, 0x6f, 0x3a, 0xd6, 0xff, 0x6f, 0x3a, 0x1b, 0x93, 0x3a, 0xfd, 0x89,
-	0xfd, 0xfc, 0x36, 0x00, 0x00, 0xff, 0xff, 0x3c, 0xbb, 0xc0, 0x75, 0x04, 0x07, 0x00, 0x00,
+	// 837 bytes of a gzipped FileDescriptorProto
+	0x1f, 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02, 0xff, 0xac, 0x55, 0xcd, 0x8e, 0xe3, 0x44,
+	0x10, 0x1e, 0x3b, 0x3f, 0x9b, 0x94, 0x07, 0x14, 0x9a, 0x15, 0x44, 0xd1, 0x2a, 0x09, 0x06, 0xa1,
+	0x00, 0x3b, 0x8e, 0x94, 0x95, 0xd0, 0x8a, 0xc3, 0x48, 0x93, 0x99, 0x95, 0x08, 0x68, 0x89, 0xd4,
+	0x1c, 0x38, 0xae, 0x1c, 0xbb, 0x93, 0xb5, 0x36, 0xe9, 0xb6, 0xec, 0xf6, 0xce, 0xe4, 0xc2, 0x81,
+	0x27, 0x40, 0xe2, 0x2d, 0x78, 0x07, 0x38, 0xef, 0x91, 0x2b, 0x1c, 0x16, 0x34, 0x3c, 0x03, 0x77,
+	0x54, 0xd5, 0x9d, 0xd8, 0x33, 0x0c, 0xd2, 0x8c, 0xe0, 0x94, 0xee, 0xaa, 0xea, 0xaf, 0xaa, 0xbe,
+	0xfa, 0xca, 0x81, 0xb6, 0x4a, 0xf3, 0x20, 0xcd, 0x94, 0x56, 0xcc, 0x4d, 0x17, 0xbd, 0xa3, 0x55,
+	0xa2, 0x9f, 0x17, 0x8b, 0x20, 0x52, 0x9b, 0xf1, 0x4a, 0xad, 0xd4, 0x98, 0x5c, 0x8b, 0x62, 0x49,
+	0x37, 0xba, 0xd0, 0xc9, 0x3c, 0xf1, 0x7f, 0x76, 0xc0, 0x9d, 0xa7, 0xec, 0x3d, 0x68, 0x26, 0x32,
+	0x2d, 0x74, 0xde, 0x75, 0x86, 0xb5, 0x91, 0x37, 0x69, 0x07, 0xe9, 0x22, 0x98, 0xa1, 0x85, 0x5b,
+	0x07, 0x1b, 0x42, 0x5d, 0x5c, 0x88, 0xa8, 0xeb, 0x0e, 0x9d, 0x91, 0x37, 0x01, 0x0c, 0x78, 0x72,
+	0x21, 0xa2, 0x79, 0xfa, 0xf9, 0x01, 0x27, 0x0f, 0xfb, 0x10, 0x9a, 0xb9, 0x2a, 0xb2, 0x48, 0x74,
+	0x6b, 0x14, 0x73, 0x88, 0x31, 0x5f, 0x93, 0x85, 0xa2, 0xac, 0x17, 0x91, 0x22, 0x95, 0x6e, 0xbb,
+	0xf5, 0x12, 0xe9, 0x54, 0xa5, 0x5b, 0x83, 0x84, 0x1e, 0xf6, 0x3e, 0x34, 0x16, 0x45, 0xb2, 0x8e,
+	0xbb, 0x0d, 0x0a, 0xf1, 0x30, 0x64, 0x8a, 0x06, 0x8a, 0x31, 0xbe, 0x69, 0x1d, 0x5c, 0x95, 0xfa,
+	0xdf, 0x42, 0x83, 0xea, 0x64, 0x5f, 0x40, 0x33, 0x4e, 0x56, 0x22, 0xd7, 0x5d, 0x67, 0xe8, 0x8c,
+	0xda, 0xd3, 0xc9, 0xab, 0xd7, 0x83, 0x83, 0xdf, 0x5e, 0x0f, 0x3e, 0xae, 0x10, 0xa2, 0x52, 0x21,
+	0x23, 0x25, 0x75, 0x98, 0x48, 0x91, 0xe5, 0xe3, 0x95, 0x3a, 0x32, 0x4f, 0x82, 0x33, 0xfa, 0xe1,
+	0x16, 0x81, 0x7d, 0x04, 0x8d, 0x44, 0xc6, 0xe2, 0x82, 0x9a, 0xad, 0x4d, 0xdf, 0xb6, 0x50, 0xde,
+	0xbc, 0xd0, 0x69, 0xa1, 0x67, 0xe8, 0xe2, 0x26, 0xc2, 0x9f, 0x41, 0xd3, 0xd0, 0xc0, 0x1e, 0x40,
+	0x7d, 0x23, 0x74, 0x48, 0xe9, 0xbd, 0x49, 0x0b, 0x6b, 0x7e, 0x2a, 0x74, 0xc8, 0xc9, 0x8a, 0x0c,
+	0x6f, 0x54, 0x21, 0x75, 0xde, 0x75, 0x4b, 0x86, 0x9f, 0xa2, 0x85, 0x5b, 0x87, 0x7f, 0x0c, 0x75,
+	0x7c, 0xc0, 0x18, 0xd4, 0xc3, 0x6c, 0x65, 0x46, 0xd1, 0xe6, 0x74, 0x66, 0x1d, 0xa8, 0x09, 0xf9,
+	0x92, 0xde, 0xb6, 0x39, 0x1e, 0xd1, 0x12, 0x9d, 0xc7, 0x44, 0x75, 0x9b, 0xe3, 0xd1, 0xff, 0xd1,
+	0x81, 0x06, 0x21, 0xb2, 0x11, 0xd6, 0x9f, 0x16, 0x86, 0x8a, 0xda, 0x94, 0xd9, 0xfa, 0x81, 0x98,
+	0xda, 0x97, 0x8f, 0xac, 0xf5, 0xa0, 0x95, 0x8b, 0xb5, 0x88, 0xb4, 0xca, 0xa8, 0xd9, 0x36, 0xdf,
+	0xdf, 0xb1, 0x8e, 0x18, 0xf9, 0x34, 0x29, 0xe8, 0xcc, 0x3e, 0x81, 0xa6, 0x22, 0x12, 0x68, 0x7a,
+	0xff, 0x42, 0x8d, 0x0d, 0x41, 0xf0, 0x4c, 0x84, 0xb1, 0x92, 0xeb, 0x2d, 0x4d, 0xb2, 0xc5, 0xf7,
+	0x77, 0xff, 0x18, 0x9a, 0x66, 0xe8, 0x6c, 0x08, 0xb5, 0x3c, 0x8b, 0xac, 0xf0, 0xde, 0xdc, 0xa9,
+	0xc1, 0xe8, 0x86, 0xa3, 0x6b, 0x5f, 0x88, 0x5b, 0x16, 0xe2, 0x73, 0x80, 0x32, 0xec, 0xff, 0x69,
+	0xd8, 0xff, 0xc1, 0x81, 0xd6, 0x4e, 0xaf, 0xac, 0x0f, 0x90, 0xc4, 0x42, 0xea, 0x64, 0x99, 0x88,
+	0xcc, 0x68, 0x8a, 0x57, 0x2c, 0xec, 0x08, 0x1a, 0xa1, 0xd6, 0xd9, 0x6e, 0x9e, 0xef, 0x56, 0xc5,
+	0x1e, 0x9c, 0xa0, 0xe7, 0x89, 0xd4, 0xd9, 0x96, 0x9b, 0xa8, 0xde, 0x63, 0x80, 0xd2, 0x88, 0xc3,
+	0x7b, 0x21, 0xb6, 0x16, 0x15, 0x8f, 0xec, 0x3e, 0x34, 0x5e, 0x86, 0xeb, 0x42, 0xd8, 0xa2, 0xcc,
+	0xe5, 0x33, 0xf7, 0xb1, 0xe3, 0xff, 0xe4, 0xc2, 0x3d, 0x2b, 0x7e, 0xf6, 0x10, 0xee, 0x91, 0xf8,
+	0x6d, 0x45, 0x37, 0x77, 0xba, 0x0b, 0x61, 0xe3, 0xfd, 0x56, 0x57, 0x6a, 0xb4, 0x50, 0x66, 0xbb,
+	0x6d, 0x8d, 0xe5, 0x8e, 0xd7, 0x62, 0xb1, 0xb4, 0xeb, 0x4b, 0xa3, 0x38, 0x13, 0xcb, 0x44, 0x26,
+	0x3a, 0x51, 0x92, 0xa3, 0x8b, 0x3d, 0xdc, 0x75, 0x5d, 0x27, 0xc4, 0x77, 0xaa, 0x88, 0xff, 0x6c,
+	0x7a, 0x06, 0x5e, 0x25, 0xcd, 0x0d, 0x5d, 0x7f, 0x50, 0xed, 0xda, 0xa6, 0x24, 0x38, 0xf3, 0xed,
+	0x29, 0x59, 0xf8, 0x0f, 0xfc, 0x7d, 0x0a, 0x50, 0x42, 0xde, 0x5e, 0x29, 0xfe, 0x5f, 0x0e, 0xc0,
+	0x3c, 0xc5, 0x8d, 0x8c, 0x43, 0x5a, 0xe0, 0xc3, 0x64, 0x25, 0x55, 0x26, 0x9e, 0x45, 0x61, 0xf4,
+	0x5c, 0xd0, 0xfb, 0x16, 0xf7, 0x8c, 0xed, 0x14, 0x4d, 0xec, 0x04, 0xbc, 0x58, 0xe4, 0x51, 0x96,
+	0xa4, 0x48, 0x98, 0x25, 0x7d, 0x80, 0x3d, 0x95, 0x38, 0xc1, 0x59, 0x19, 0x61, 0xb8, 0xaa, 0xbe,
+	0x61, 0x27, 0xf0, 0xd6, 0xb9, 0xca, 0x5e, 0x88, 0xec, 0x59, 0xa4, 0x64, 0xae, 0xb3, 0x30, 0x91,
+	0xda, 0xce, 0xe3, 0x3e, 0x02, 0x7d, 0x43, 0xce, 0xd3, 0xbd, 0x8f, 0x77, 0xce, 0xaf, 0x59, 0x7a,
+	0xc7, 0xd0, 0xb9, 0x9e, 0xe3, 0x4e, 0x7c, 0x3d, 0x82, 0xce, 0xf5, 0x2c, 0x6c, 0x00, 0x9e, 0x2d,
+	0x4b, 0x86, 0x1b, 0xb1, 0xdb, 0x06, 0x63, 0xfa, 0x2a, 0xdc, 0x08, 0xff, 0x57, 0x07, 0xa0, 0xd4,
+	0x0a, 0xe6, 0x43, 0x21, 0xe1, 0x4e, 0x1f, 0x1a, 0xe1, 0xac, 0xa1, 0xb5, 0xb1, 0x14, 0x58, 0x62,
+	0x1e, 0x5c, 0xd5, 0x57, 0xb0, 0x63, 0x88, 0x2a, 0x36, 0x9f, 0xef, 0xef, 0x7e, 0xbf, 0xd3, 0xe7,
+	0x7b, 0x9f, 0xa1, 0xf7, 0x25, 0xbc, 0x71, 0x05, 0xee, 0x96, 0xd2, 0x2b, 0xc7, 0x54, 0x21, 0x64,
+	0xda, 0x79, 0x75, 0xd9, 0x77, 0x7e, 0xb9, 0xec, 0x3b, 0x7f, 0x5c, 0xf6, 0x9d, 0xef, 0xff, 0xec,
+	0x1f, 0x2c, 0x9a, 0xf4, 0xe7, 0xf9, 0xe8, 0xef, 0x00, 0x00, 0x00, 0xff, 0xff, 0x52, 0xfa, 0x2a,
+	0xaf, 0x7c, 0x07, 0x00, 0x00,
 }
diff --git a/solver/pb/ops.proto b/solver/pb/ops.proto
index ada3b65a60803..4ec2c9209efab 100644
--- a/solver/pb/ops.proto
+++ b/solver/pb/ops.proto
@@ -74,6 +74,13 @@ message OpMetadata {
 	// Description can be used for keeping any text fields that builder doesn't parse
 	map<string, string> description = 2;  
 	// TODO: add worker constraint, etc.
+	WorkerConstraint worker_constraint = 3;
+}
+
+// WorkerConstraint is WIP. Will be changed.
+message WorkerConstraint {
+	string worker_name = 1; // e.g. "runc-overlay", "containerd-overlay", "containerd-btrfs"
+// TODO: distributed mode
 }
 
 // Definition is the LLB definition structure with per-vertex metadata entries
diff --git a/solver/solver.go b/solver/solver.go
index 6bec60a80d7d1..12b73d6ef64f4 100644
--- a/solver/solver.go
+++ b/solver/solver.go
@@ -11,13 +11,13 @@ import (
 	"github.com/moby/buildkit/cache/cacheimport"
 	"github.com/moby/buildkit/cache/contenthash"
 	"github.com/moby/buildkit/client"
+	"github.com/moby/buildkit/executor"
 	"github.com/moby/buildkit/exporter"
 	"github.com/moby/buildkit/frontend"
+	"github.com/moby/buildkit/metaworker"
 	"github.com/moby/buildkit/solver/pb"
-	"github.com/moby/buildkit/source"
 	"github.com/moby/buildkit/util/bgfunc"
 	"github.com/moby/buildkit/util/progress"
-	"github.com/moby/buildkit/worker"
 	digest "github.com/opencontainers/go-digest"
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
@@ -26,30 +26,27 @@ import (
 )
 
 type LLBOpt struct {
-	SourceManager    *source.Manager
-	CacheManager     cache.Manager
-	Worker           worker.Worker
-	InstructionCache InstructionCache
-	ImageSource      source.Source
-	Frontends        map[string]frontend.Frontend // used by nested invocations
-	CacheExporter    *cacheimport.CacheExporter
-	CacheImporter    *cacheimport.CacheImporter
+	// FIXME mw0
+	// multi-worker is not supported; the default one is always used.
+	MetaWorkers []*metaworker.MetaWorker
+	Frontends   map[string]frontend.Frontend // used by nested invocations
 }
 
 func NewLLBSolver(opt LLBOpt) *Solver {
 	var s *Solver
+	// FIXME mw0
 	s = New(func(v Vertex) (Op, error) {
 		switch op := v.Sys().(type) {
 		case *pb.Op_Source:
-			return newSourceOp(v, op, opt.SourceManager)
+			return newSourceOp(v, op, opt.MetaWorkers[0].SourceManager)
 		case *pb.Op_Exec:
-			return newExecOp(v, op, opt.CacheManager, opt.Worker)
+			return newExecOp(v, op, opt.MetaWorkers[0].CacheManager, opt.MetaWorkers[0].Executor)
 		case *pb.Op_Build:
 			return newBuildOp(v, op, s)
 		default:
 			return nil, nil
 		}
-	}, opt.InstructionCache, opt.ImageSource, opt.Worker, opt.CacheManager, opt.Frontends, opt.CacheExporter, opt.CacheImporter)
+	}, opt.MetaWorkers, opt.Frontends)
 	return s
 }
 
@@ -86,17 +83,14 @@ type InstructionCache interface {
 type Solver struct {
 	resolve     ResolveOpFunc
 	jobs        *jobList
-	cache       InstructionCache
-	imageSource source.Source
-	worker      worker.Worker
-	cm          cache.Manager // TODO: remove with immutableRef.New()
+	metaworkers []*metaworker.MetaWorker
 	frontends   map[string]frontend.Frontend
-	ce          *cacheimport.CacheExporter
-	ci          *cacheimport.CacheImporter
 }
 
-func New(resolve ResolveOpFunc, cache InstructionCache, imageSource source.Source, worker worker.Worker, cm cache.Manager, f map[string]frontend.Frontend, ce *cacheimport.CacheExporter, ci *cacheimport.CacheImporter) *Solver {
-	return &Solver{resolve: resolve, jobs: newJobList(), cache: cache, imageSource: imageSource, worker: worker, cm: cm, frontends: f, ce: ce, ci: ci}
+// FIXME mw0
+// multi-worker is not supported; the default one is always used.
+func New(resolve ResolveOpFunc, mw []*metaworker.MetaWorker, f map[string]frontend.Frontend) *Solver {
+	return &Solver{resolve: resolve, jobs: newJobList(), metaworkers: mw, frontends: f}
 }
 
 type SolveRequest struct {
@@ -125,7 +119,8 @@ func (s *Solver) solve(ctx context.Context, j *job, req SolveRequest) (Reference
 }
 
 func (s *Solver) llbBridge(j *job) *llbBridge {
-	return &llbBridge{job: j, Solver: s, resolveImageConfig: s.imageSource.(resolveImageConfig)}
+	// FIXME mw0
+	return &llbBridge{job: j, Solver: s, resolveImageConfig: s.metaworkers[0].ImageSource.(resolveImageConfig)}
 }
 
 func (s *Solver) Solve(ctx context.Context, id string, req SolveRequest) error {
@@ -135,16 +130,17 @@ func (s *Solver) Solve(ctx context.Context, id string, req SolveRequest) error {
 	pr, ctx, closeProgressWriter := progress.NewContext(ctx)
 	defer closeProgressWriter()
 
+	// FIXME mw0
 	if importRef := req.ImportCacheRef; importRef != "" {
-		cache, err := s.ci.Import(ctx, importRef)
+		cache, err := s.metaworkers[0].CacheImporter.Import(ctx, importRef)
 		if err != nil {
 			return err
 		}
-		s.cache = mergeRemoteCache(s.cache, cache)
+		s.metaworkers[0].InstructionCache = mergeRemoteCache(s.metaworkers[0].InstructionCache, cache)
 	}
 
 	// register a build job. vertex needs to be loaded to a job to run
-	ctx, j, err := s.jobs.new(ctx, id, pr, s.cache)
+	ctx, j, err := s.jobs.new(ctx, id, pr, s.metaworkers[0].InstructionCache)
 	if err != nil {
 		return err
 	}
@@ -193,7 +189,8 @@ func (s *Solver) Solve(ctx context.Context, id string, req SolveRequest) error {
 				return err
 			}
 
-			return s.ce.Export(ctx, records, exportName)
+			// FIXME mw0
+			return s.metaworkers[0].CacheExporter.Export(ctx, records, exportName)
 		}); err != nil {
 			return err
 		}
@@ -232,7 +229,8 @@ func (s *Solver) subBuild(ctx context.Context, dgst digest.Digest, req SolveRequ
 	st = jl.actives[inp.Vertex.Digest()]
 	jl.mu.Unlock()
 
-	return getRef(ctx, st.solver, inp.Vertex.(*vertex), inp.Index, s.cache) // TODO: combine to pass single input                                        // TODO: export cache for subbuilds
+	//FIXME mw0
+	return getRef(ctx, st.solver, inp.Vertex.(*vertex), inp.Index, s.metaworkers[0].InstructionCache) // TODO: combine to pass single input                                        // TODO: export cache for subbuilds
 }
 
 type VertexSolver interface {
@@ -814,13 +812,15 @@ func (s *llbBridge) Solve(ctx context.Context, req frontend.SolveRequest) (cache
 	return immutable, exp, nil
 }
 
-func (s *llbBridge) Exec(ctx context.Context, meta worker.Meta, rootFS cache.ImmutableRef, stdin io.ReadCloser, stdout, stderr io.WriteCloser) error {
-	active, err := s.cm.New(ctx, rootFS)
+func (s *llbBridge) Exec(ctx context.Context, meta executor.Meta, rootFS cache.ImmutableRef, stdin io.ReadCloser, stdout, stderr io.WriteCloser) error {
+	// FIXME mw0
+	mw0 := s.metaworkers[0]
+	active, err := mw0.CacheManager.New(ctx, rootFS)
 	if err != nil {
 		return err
 	}
 	defer active.Release(context.TODO())
-	return s.worker.Exec(ctx, meta, active, nil, stdin, stdout, stderr)
+	return mw0.Executor.Exec(ctx, meta, active, nil, stdin, stdout, stderr)
 }
 
 func cacheKeyForIndex(dgst digest.Digest, index Index) digest.Digest {
diff --git a/solver/vertex.go b/solver/vertex.go
index fcd0a73b11dda..71cebc8fe0992 100644
--- a/solver/vertex.go
+++ b/solver/vertex.go
@@ -6,6 +6,7 @@ import (
 
 	"github.com/moby/buildkit/client"
 	"github.com/moby/buildkit/identity"
+	"github.com/moby/buildkit/solver/pb"
 	"github.com/moby/buildkit/util/progress"
 	digest "github.com/opencontainers/go-digest"
 	"golang.org/x/net/context"
@@ -18,17 +19,13 @@ type Vertex interface {
 	// Sys returns an internal value that is used to execute the vertex. Usually
 	// this is capured by the operation resolver method during solve.
 	Sys() interface{}
-	Metadata() Metadata
+	// FIXME(AkihiroSuda): we should not import pb pkg here.
+	Metadata() *pb.OpMetadata
 	// Array of vertexes current vertex depends on.
 	Inputs() []Input
 	Name() string // change this to general metadata
 }
 
-// Metadata is per-vertex metadata, implemented by *pb.OpMetadata
-type Metadata interface {
-	GetIgnoreCache() bool
-}
-
 type Index int
 
 // Input is an pointer to a single reference from a vertex by an index.
@@ -45,7 +42,7 @@ type input struct {
 type vertex struct {
 	mu           sync.Mutex
 	sys          interface{}
-	metadata     Metadata
+	metadata     *pb.OpMetadata
 	inputs       []*input
 	err          error
 	digest       digest.Digest
@@ -74,7 +71,7 @@ func (v *vertex) Sys() interface{} {
 	return v.sys
 }
 
-func (v *vertex) Metadata() Metadata {
+func (v *vertex) Metadata() *pb.OpMetadata {
 	return v.metadata
 }