kubeadm: Add a preflight check that the control-plane node has at least 1700MB of RAM

cmd/kubeadm/app/constants/constants.go

@@ -350,6 +350,10 @@ const (
 	// ControlPlaneNumCPU is the number of CPUs required on control-plane
 	ControlPlaneNumCPU = 2
 
+	// ControlPlaneMem is the number of megabytes of memory required on the control-plane
+	// Below that amount of RAM running a stable control plane would be difficult.
+	ControlPlaneMem = 1700
+
 	// KubeadmCertsSecret specifies in what Secret in the kube-system namespace the certificates should be stored
 	KubeadmCertsSecret = "kubeadm-certs"
 

cmd/kubeadm/app/preflight/checks.go

@@ -869,6 +869,16 @@ func (ncc NumCPUCheck) Check() (warnings, errorList []error) {
 	return warnings, errorList
 }
 
+// MemCheck checks if the number of megabytes of memory is not less than required
+type MemCheck struct {
+	Mem uint64
+}
+
+// Name returns the label for memory
+func (MemCheck) Name() string {
+	return "Mem"
+}
+
 // RunInitNodeChecks executes all individual, applicable to control-plane node checks.
 // The boolean flag 'isSecondaryControlPlane' controls whether we are running checks in a --join-control-plane scenario.
 // The boolean flag 'downloadCerts' controls whether we should skip checks on certificates because we are downloading them.
@@ -884,6 +894,9 @@ func RunInitNodeChecks(execer utilsexec.Interface, cfg *kubeadmapi.InitConfigura
 	manifestsDir := filepath.Join(kubeadmconstants.KubernetesDir, kubeadmconstants.ManifestsSubDirName)
 	checks := []Checker{
 		NumCPUCheck{NumCPU: kubeadmconstants.ControlPlaneNumCPU},
+		// Linux only
+		// TODO: support other OS, if control-plane is supported on it.
+		MemCheck{Mem: kubeadmconstants.ControlPlaneMem},
 		KubernetesVersionCheck{KubernetesVersion: cfg.KubernetesVersion, KubeadmVersion: kubeadmversion.Get().GitVersion},
 		FirewalldCheck{ports: []int{int(cfg.LocalAPIEndpoint.BindPort), kubeadmconstants.KubeletPort}},
 		PortOpenCheck{port: int(cfg.LocalAPIEndpoint.BindPort)},

cmd/kubeadm/app/preflight/checks_darwin.go

@@ -25,3 +25,9 @@ package preflight
 func (idsc IsDockerSystemdCheck) Check() (warnings, errorList []error) {
 	return nil, nil
 }
+
+// Check number of memory required by kubeadm
+// No-op for Darwin (MacOS).
+func (mc MemCheck) Check() (warnings, errorList []error) {
+	return nil, nil
+}

cmd/kubeadm/app/preflight/checks_linux.go

@@ -19,6 +19,8 @@ limitations under the License.
 package preflight
 
 import (
+	"syscall"
+
 	"github.com/pkg/errors"
 	kubeadmutil "k8s.io/kubernetes/cmd/kubeadm/app/util"
 	"k8s.io/utils/exec"
@@ -40,3 +42,19 @@ func (idsc IsDockerSystemdCheck) Check() (warnings, errorList []error) {
 	}
 	return nil, nil
 }
+
+// Check number of memory required by kubeadm
+func (mc MemCheck) Check() (warnings, errorList []error) {
+	info := syscall.Sysinfo_t{}
+	err := syscall.Sysinfo(&info)
+	if err != nil {
+		errorList = append(errorList, errors.Wrapf(err, "failed to get system info"))
+	}
+
+	// Totalram returns bytes; convert to MB
+	actual := uint64(info.Totalram) / 1024 / 1024
+	if actual < mc.Mem {
+		errorList = append(errorList, errors.Errorf("the system RAM (%d MB) is less than the minimum %d MB", actual, mc.Mem))
+	}
+	return warnings, errorList
+}

cmd/kubeadm/app/preflight/checks_test.go

@@ -20,6 +20,7 @@ import (
 	"bytes"
 	"fmt"
 	"io/ioutil"
+	"runtime"
 	"strings"
 	"testing"
 
@@ -849,3 +850,29 @@ func TestNumCPUCheck(t *testing.T) {
 		})
 	}
 }
+
+func TestMemCheck(t *testing.T) {
+	// skip this test, if OS in not Linux, since it will ONLY pass on Linux.
+	if runtime.GOOS != "linux" {
+		t.Skip("unsupported OS for memory check test ")
+	}
+
+	var tests = []struct {
+		minimum        uint64
+		expectedErrors int
+	}{
+		{0, 0},
+		{9999999999999999, 1},
+	}
+
+	for _, rt := range tests {
+		t.Run(fmt.Sprintf("MemoryCheck{%d}", rt.minimum), func(t *testing.T) {
+			warnings, errors := MemCheck{Mem: rt.minimum}.Check()
+			if len(warnings) > 0 {
+				t.Errorf("expected 0 warnings but got %d: %q", len(warnings), warnings)
+			} else if len(errors) != rt.expectedErrors {
+				t.Errorf("expected %d error(s) but got %d: %q", rt.expectedErrors, len(errors), errors)
+			}
+		})
+	}
+}

cmd/kubeadm/app/preflight/checks_windows.go

@@ -54,3 +54,9 @@ func (ipuc IsPrivilegedUserCheck) Check() (warnings, errorList []error) {
 func (idsc IsDockerSystemdCheck) Check() (warnings, errorList []error) {
 	return nil, nil
 }
+
+// Check number of memory required by kubeadm
+// No-op for Windows.
+func (mc MemCheck) Check() (warnings, errorList []error) {
+	return nil, nil
+}