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[AWS] Favor subnets w/ more IP addresses when launching instances #1413

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Feb 24, 2022
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6 changes: 3 additions & 3 deletions pkg/cloudprovider/aws/fake/ec2api.go
Original file line number Diff line number Diff line change
Expand Up @@ -180,11 +180,11 @@ func (e *EC2API) DescribeSubnetsWithContext(context.Context, *ec2.DescribeSubnet
return e.DescribeSubnetsOutput, nil
}
return &ec2.DescribeSubnetsOutput{Subnets: []*ec2.Subnet{
{SubnetId: aws.String("test-subnet-1"), AvailabilityZone: aws.String("test-zone-1a"),
{SubnetId: aws.String("test-subnet-1"), AvailabilityZone: aws.String("test-zone-1a"), AvailableIpAddressCount: aws.Int64(100),
Tags: []*ec2.Tag{{Key: aws.String("Name"), Value: aws.String("test-subnet-1")}}},
{SubnetId: aws.String("test-subnet-2"), AvailabilityZone: aws.String("test-zone-1b"),
{SubnetId: aws.String("test-subnet-2"), AvailabilityZone: aws.String("test-zone-1b"), AvailableIpAddressCount: aws.Int64(100),
Tags: []*ec2.Tag{{Key: aws.String("Name"), Value: aws.String("test-subnet-2")}}},
{SubnetId: aws.String("test-subnet-3"), AvailabilityZone: aws.String("test-zone-1c"),
{SubnetId: aws.String("test-subnet-3"), AvailabilityZone: aws.String("test-zone-1c"), AvailableIpAddressCount: aws.Int64(100),
Tags: []*ec2.Tag{{Key: aws.String("Name"), Value: aws.String("test-subnet-3")}, {Key: aws.String("TestTag")}}},
}}, nil
}
Expand Down
46 changes: 26 additions & 20 deletions pkg/cloudprovider/aws/instance.go
Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,7 @@ package aws
import (
"context"
"fmt"
"sort"
"strings"
"time"

Expand Down Expand Up @@ -180,6 +181,14 @@ func (p *InstanceProvider) getLaunchTemplateConfigs(ctx context.Context, constra
// getOverrides creates and returns launch template overrides for the cross product of instanceTypeOptions and subnets (with subnets being constrained by
// zones and the offerings in instanceTypeOptions)
func (p *InstanceProvider) getOverrides(instanceTypeOptions []cloudprovider.InstanceType, subnets []*ec2.Subnet, zones sets.String, capacityType string) []*ec2.FleetLaunchTemplateOverridesRequest {
// sort subnets in ascending order of available IP addresses and populate map with most available subnet per AZ
zonalSubnets := map[string]*ec2.Subnet{}
sort.Slice(subnets, func(i, j int) bool {
return aws.Int64Value(subnets[i].AvailableIpAddressCount) < aws.Int64Value(subnets[j].AvailableIpAddressCount)
})
for _, subnet := range subnets {
zonalSubnets[*subnet.AvailabilityZone] = subnet
}
var overrides []*ec2.FleetLaunchTemplateOverridesRequest
for i, instanceType := range instanceTypeOptions {
for _, offering := range instanceType.Offerings() {
Expand All @@ -189,27 +198,24 @@ func (p *InstanceProvider) getOverrides(instanceTypeOptions []cloudprovider.Inst
if !zones.Has(offering.Zone) {
continue
}
for _, subnet := range subnets {
if aws.StringValue(subnet.AvailabilityZone) != offering.Zone {
continue
}
override := &ec2.FleetLaunchTemplateOverridesRequest{
InstanceType: aws.String(instanceType.Name()),
SubnetId: subnet.SubnetId,
// This is technically redundant, but is useful if we have to parse insufficient capacity errors from
// CreateFleet so that we can figure out the zone rather than additional API calls to look up the subnet
AvailabilityZone: subnet.AvailabilityZone,
}
// Add a priority for spot requests since we are using the capacity-optimized-prioritized spot allocation strategy
// to reduce the likelihood of getting an excessively large instance type.
// instanceTypeOptions are sorted by vcpus and memory so this prioritizes smaller instance types.
if capacityType == v1alpha1.CapacityTypeSpot {
override.Priority = aws.Float64(float64(i))
}
overrides = append(overrides, override)
// FleetAPI cannot span subnets from the same AZ, so break after the first one.
break
subnet, ok := zonalSubnets[offering.Zone]
if !ok {
continue
}
override := &ec2.FleetLaunchTemplateOverridesRequest{
InstanceType: aws.String(instanceType.Name()),
SubnetId: subnet.SubnetId,
// This is technically redundant, but is useful if we have to parse insufficient capacity errors from
// CreateFleet so that we can figure out the zone rather than additional API calls to look up the subnet
AvailabilityZone: subnet.AvailabilityZone,
}
// Add a priority for spot requests since we are using the capacity-optimized-prioritized spot allocation strategy
// to reduce the likelihood of getting an excessively large instance type.
// instanceTypeOptions are sorted by vcpus and memory so this prioritizes smaller instance types.
if capacityType == v1alpha1.CapacityTypeSpot {
override.Priority = aws.Float64(float64(i))
}
overrides = append(overrides, override)
}
}
return overrides
Expand Down
21 changes: 20 additions & 1 deletion pkg/cloudprovider/aws/suite_test.go
Original file line number Diff line number Diff line change
Expand Up @@ -55,6 +55,7 @@ var opts options.Options
var env *test.Environment
var launchTemplateCache *cache.Cache
var securityGroupCache *cache.Cache
var subnetCache *cache.Cache
var unavailableOfferingsCache *cache.Cache
var fakeEC2API *fake.EC2API
var provisioners *provisioning.Controller
Expand All @@ -80,8 +81,12 @@ var _ = BeforeSuite(func() {
launchTemplateCache = cache.New(CacheTTL, CacheCleanupInterval)
unavailableOfferingsCache = cache.New(InsufficientCapacityErrorCacheTTL, InsufficientCapacityErrorCacheCleanupInterval)
securityGroupCache = cache.New(CacheTTL, CacheCleanupInterval)
subnetCache = cache.New(CacheTTL, CacheCleanupInterval)
fakeEC2API = &fake.EC2API{}
subnetProvider := NewSubnetProvider(fakeEC2API)
subnetProvider := &SubnetProvider{
ec2api: fakeEC2API,
cache: subnetCache,
}
instanceTypeProvider := &InstanceTypeProvider{
ec2api: fakeEC2API,
subnetProvider: subnetProvider,
Expand Down Expand Up @@ -131,6 +136,7 @@ var _ = Describe("Allocation", func() {
fakeEC2API.Reset()
launchTemplateCache.Flush()
securityGroupCache.Flush()
subnetCache.Flush()
unavailableOfferingsCache.Flush()
})

Expand Down Expand Up @@ -448,6 +454,19 @@ var _ = Describe("Allocation", func() {
&ec2.FleetLaunchTemplateOverridesRequest{SubnetId: aws.String("test-subnet-3"), InstanceType: aws.String("m5.large"), AvailabilityZone: aws.String("test-zone-1c")},
))
})
It("should launch instances into subnet with the most available IP addresses", func() {
fakeEC2API.DescribeSubnetsOutput = &ec2.DescribeSubnetsOutput{Subnets: []*ec2.Subnet{
{SubnetId: aws.String("test-subnet-1"), AvailabilityZone: aws.String("test-zone-1a"), AvailableIpAddressCount: aws.Int64(10),
Tags: []*ec2.Tag{{Key: aws.String("Name"), Value: aws.String("test-subnet-1")}}},
{SubnetId: aws.String("test-subnet-2"), AvailabilityZone: aws.String("test-zone-1a"), AvailableIpAddressCount: aws.Int64(100),
Tags: []*ec2.Tag{{Key: aws.String("Name"), Value: aws.String("test-subnet-2")}}},
}}

pod := ExpectProvisioned(ctx, env.Client, selectionController, provisioners, provisioner, test.UnschedulablePod(test.PodOptions{NodeSelector: map[string]string{v1.LabelTopologyZone: "test-zone-1a"}}))[0]
ExpectScheduled(ctx, env.Client, pod)
createFleetInput := fakeEC2API.CalledWithCreateFleetInput.Pop().(*ec2.CreateFleetInput)
Expect(aws.StringValue(createFleetInput.LaunchTemplateConfigs[0].Overrides[0].SubnetId)).To(Equal("test-subnet-2"))
})
})
Context("Security Groups", func() {
It("should default to the clusters security groups", func() {
Expand Down
2 changes: 1 addition & 1 deletion website/content/en/preview/AWS/provisioning.md
Original file line number Diff line number Diff line change
Expand Up @@ -41,7 +41,7 @@ Karpenter discovers subnets using [AWS tags](https://docs.aws.amazon.com/AWSEC2/

Subnets may be specified by any AWS tag, including `Name`. Selecting tag values using wildcards ("\*") is supported.

When launching nodes, Karpenter automatically chooses a subnet that matches the desired zone. If multiple subnets exist for a zone, one is chosen randomly.
When launching nodes, Karpenter automatically chooses a subnet that matches the desired zone. If multiple subnets exist for a zone, the one with the most available IP addresses will be used.

**Examples**

Expand Down