AWS CNI Mode

✨ new operational mode of Direct Ingress Pod access

This adds a new operational mode of adding the Ingress pods as Targets in the Target Groups directly, instead of the nodes where the Ingress is accessed through a node port.

The core idea is based on the fact that standard AWS EKS cluster running AWS VPC CNI have their pods as first class members in the VPCs. Their IPs are directly reachable from the ALB/NLB target groups like the nodes are too, which means there is no necessity for the NodePort extra hop to take.

There are several drivers and advantages accessing the pod directly vs a Nodeport:

## Delay and eventual consistency of AutoscalingGroup to ALB/NLB target group updates

This has been the biggest trouble in operations, that the list of nodes in target groups is slower than the nodes are replaced which ends up in a black hole of no Ingresses available at a time. We are facing regularily downtimes especially when spot interruptions or ASG node rollings happen that the ALB/NLB takes up to 2 minutes to reflect the group change. For smaller clusters this leads to no Skipper instance being registered hence no target available to forward traffic.
With this new mode the registration happens independently and instantly, the registration of targets up to be serving takes less than 10seconds!

## independent scaling of nodes

With nodeports there is an eventual dependency on available nodes to scale the Ingress.
Plus the Ingress pod cannot be replaced in place but requires a termination first and then rescheduling. For a certain time which can be more than a minute, this node is offline as an Ingress.
With this mode the host networking and node port is obsolete, which allows node indepent scaling of Skipper pods! Skipper becomes a regular deployment and its replicaSet can be indepent on the cluster size.

## Save de/registering and instantaneous response

Core idea is the event based registration to Kubernetes using pod `Informer` that receives immediate notifications about pod changes, which allow almost zero delayed updates on the target groups.

The registration happens as soon as the pod received an IP from AWS VPC. Hence the readiness probe of the ALB/NLB starts to monitor already during scheduling of the pod, serving the earliest possible. Tests in lab show pods serving ALB traffic well under 10s from scheduling!

Deregistration happens bound to the kubernetes event. That means the LB is now in sync with the cluster and will stop sending traffic before the pod is actually terminated. This implement save deregistering without traffic loss.

## TG without unhealthy targets

Since the IP based TGs are managed now by this controller, they represent pods and thus all of them are shown healthy, otherwise removed by this controller.

# Implementation details:

* client-go Informer: This high level functions are providing a convenient access to event registrations of kubernetes. Since the event registration is the key of fast response and efficient compared to high rate polling, using this standard factory methods seems standing to reason.

## Todo

Settle on the impelemtation agreement and finish it up by adding unit tests.

## Tests

*  successful transistion of TG from type Instance to type IP vice versa
* the controller registers pods that are discovered
* the controller deregisters pods that are "terminating" status
* the controller recovers desired state if manual intervention on the TG happened by "resyncing"
* it removes pods that are killed or dead

## misc

* extended the service account with required RBAC permissions to watch/list pods
* added example of Skipper without a HostNetwork and NodePort

aws/adapter.go

@@ -74,6 +74,14 @@ type Adapter struct {
 	denyInternalRespBody        string
 	denyInternalRespContentType string
 	denyInternalRespStatusCode  int
+	TargetCNI                   targetCNIconfig
+}
+
+type targetCNIconfig struct {
+	Enabled         bool
+	Endpoints       []string
+	TargetGroupARNs []string
+	TargetGroupCh   chan []string
 }
 
 type manifest struct {
@@ -124,11 +132,14 @@ const (
 	DefaultNLBCrossZone   = false
 	DefaultNLBHTTPEnabled = false
 
-	nameTag                     = "Name"
-	LoadBalancerTypeApplication = "application"
-	LoadBalancerTypeNetwork     = "network"
-	IPAddressTypeIPV4           = "ipv4"
-	IPAddressTypeDualstack      = "dualstack"
+	nameTag                       = "Name"
+	LoadBalancerTypeApplication   = "application"
+	LoadBalancerTypeNetwork       = "network"
+	IPAddressTypeIPV4             = "ipv4"
+	IPAddressTypeDualstack        = "dualstack"
+	TargetAccessModeAWSCNI        = "AWSCNI"
+	TargetAccessModeNodePort      = "NodePort"
+	DefaultTargetCNILabelSelector = "kube-system/application=skipper-ingress"
 )
 
 var (
@@ -225,6 +236,10 @@ func NewAdapter(clusterID, newControllerID, vpcID string, debug, disableInstrume
 		nlbCrossZone:               DefaultNLBCrossZone,
 		nlbHTTPEnabled:             DefaultNLBHTTPEnabled,
 		customFilter:               DefaultCustomFilter,
+		TargetCNI: targetCNIconfig{
+			Enabled:       false,
+			TargetGroupCh: make(chan []string, 10),
+		},
 	}
 
 	adapter.manifest, err = buildManifest(adapter, clusterID, vpcID)
@@ -432,6 +447,15 @@ func (a *Adapter) WithInternalDomains(domains []string) *Adapter {
 	return a
 }
 
+// WithTargetAccessMode returns the receiver adapter after defining the target access mode
+func (a *Adapter) WithTargetAccessMode(t string) *Adapter {
+	a.TargetCNI.Enabled = false
+	if t == TargetAccessModeAWSCNI {
+		a.TargetCNI.Enabled = true
+	}
+	return a
+}
+
 // WithDenyInternalDomains returns the receiver adapter after setting
 // the denyInternalDomains config.
 func (a *Adapter) WithDenyInternalDomains(deny bool) *Adapter {
@@ -568,14 +592,26 @@ func (a *Adapter) UpdateTargetGroupsAndAutoScalingGroups(stacks []*Stack, proble
 		return
 	}
 
+	// split the full list into relevant TG types
+	targetTypesARNs, err := categorizeTargetTypeInstance(a.elbv2, targetGroupARNs)
+	if err != nil {
+		problems.Add("failed to categorize Target Type Instance: %w", err)
+		return
+	}
+
+	// update the CNI TG list
+	if a.TargetCNI.Enabled {
+		a.TargetCNI.TargetGroupCh <- targetTypesARNs[elbv2.TargetTypeEnumIp]
+	}
+
 	ownerTags := map[string]string{
 		clusterIDTagPrefix + a.ClusterID(): resourceLifecycleOwned,
 		kubernetesCreatorTag:               a.controllerID,
 	}
 
 	for _, asg := range a.TargetedAutoScalingGroups {
 		// This call is idempotent and safe to execute every time
-		if err := updateTargetGroupsForAutoScalingGroup(a.autoscaling, a.elbv2, targetGroupARNs, asg.name, ownerTags); err != nil {
+		if err := updateTargetGroupsForAutoScalingGroup(a.autoscaling, a.elbv2, targetTypesARNs[elbv2.TargetTypeEnumInstance], asg.name, ownerTags); err != nil {
 			problems.Add("failed to update target groups for autoscaling group %q: %w", asg.name, err)
 		}
 	}
@@ -592,13 +628,13 @@ func (a *Adapter) UpdateTargetGroupsAndAutoScalingGroups(stacks []*Stack, proble
 	runningSingleInstances := a.RunningSingleInstances()
 	if len(runningSingleInstances) != 0 {
 		// This call is idempotent too
-		if err := registerTargetsOnTargetGroups(a.elbv2, targetGroupARNs, runningSingleInstances); err != nil {
+		if err := registerTargetsOnTargetGroups(a.elbv2, targetTypesARNs[elbv2.TargetTypeEnumInstance], runningSingleInstances); err != nil {
 			problems.Add("failed to register instances %q in target groups: %w", runningSingleInstances, err)
 		}
 	}
 	if len(a.obsoleteInstances) != 0 {
 		// Deregister instances from target groups and clean up list of obsolete instances
-		if err := deregisterTargetsOnTargetGroups(a.elbv2, targetGroupARNs, a.obsoleteInstances); err != nil {
+		if err := deregisterTargetsOnTargetGroups(a.elbv2, targetTypesARNs[elbv2.TargetTypeEnumInstance], a.obsoleteInstances); err != nil {
 			problems.Add("failed to deregister instances %q in target groups: %w", a.obsoleteInstances, err)
 		} else {
 			a.obsoleteInstances = make([]string, 0)
@@ -665,6 +701,7 @@ func (a *Adapter) CreateStack(certificateARNs []string, scheme, securityGroup, o
 		http2:                             http2,
 		tags:                              a.stackTags,
 		internalDomains:                   a.internalDomains,
+		targetAccessModeCNI:               a.TargetCNI.Enabled,
 		denyInternalDomains:               a.denyInternalDomains,
 		denyInternalDomainsResponse: denyResp{
 			body:        a.denyInternalRespBody,
@@ -720,6 +757,7 @@ func (a *Adapter) UpdateStack(stackName string, certificateARNs map[string]time.
 		http2:                             http2,
 		tags:                              a.stackTags,
 		internalDomains:                   a.internalDomains,
+		targetAccessModeCNI:               a.TargetCNI.Enabled,
 		denyInternalDomains:               a.denyInternalDomains,
 		denyInternalDomainsResponse: denyResp{
 			body:        a.denyInternalRespBody,
@@ -1009,3 +1047,54 @@ func nonTargetedASGs(ownedASGs, targetedASGs map[string]*autoScalingGroupDetails
 
 	return nonTargetedASGs
 }
+
+// SetTargetsOnCNITargetGroups implements desired state for CNI target groups
+// by polling the current list of targets thus creating a diff of what needs to be added and removed.
+func (a *Adapter) SetTargetsOnCNITargetGroups() error {
+	if a.TargetCNI.TargetGroupARNs == nil || len(a.TargetCNI.TargetGroupARNs) == 0 {
+		log.Info("No target group ARNs cached for CNI")
+		return nil
+	}
+	for _, targetGroupARN := range a.TargetCNI.TargetGroupARNs {
+		tgh, err := a.elbv2.DescribeTargetHealth(&elbv2.DescribeTargetHealthInput{TargetGroupArn: &targetGroupARN})
+		if err != nil {
+			return fmt.Errorf("unable to describe target health %w", err)
+		}
+		registeredInstances := make([]string, len(tgh.TargetHealthDescriptions))
+		for i, target := range tgh.TargetHealthDescriptions {
+			registeredInstances[i] = *target.Target.Id
+		}
+		toregister := difference(a.TargetCNI.Endpoints, registeredInstances)
+		if len(toregister) > 0 {
+			log.Info("Registering CNI targets: ", toregister)
+			err := registerTargetsOnTargetGroups(a.elbv2, a.TargetCNI.TargetGroupARNs, toregister)
+			if err != nil {
+				return err
+			}
+		}
+		toderegister := difference(registeredInstances, a.TargetCNI.Endpoints)
+		if len(toderegister) > 0 {
+			log.Info("Deregistering CNI targets: ", toderegister)
+			err := deregisterTargetsOnTargetGroups(a.elbv2, a.TargetCNI.TargetGroupARNs, toderegister)
+			if err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
+// difference returns the elements in `a` that aren't in `b`.
+func difference(a, b []string) []string {
+	mb := make(map[string]struct{}, len(b))
+	for _, x := range b {
+		mb[x] = struct{}{}
+	}
+	var diff []string
+	for _, x := range a {
+		if _, found := mb[x]; !found {
+			diff = append(diff, x)
+		}
+	}
+	return diff
+}

aws/asg.go

@@ -260,6 +260,25 @@ func describeTargetGroups(elbv2svc elbv2iface.ELBV2API) (map[string]struct{}, er
 	return targetGroups, err
 }
 
+// map the target group slice into specific types such as instance, ip, etc
+func categorizeTargetTypeInstance(elbv2svc elbv2iface.ELBV2API, allTGARNs []string) (map[string][]string, error) {
+	targetTypes := make(map[string][]string)
+	err := elbv2svc.DescribeTargetGroupsPagesWithContext(context.TODO(), &elbv2.DescribeTargetGroupsInput{},
+		func(resp *elbv2.DescribeTargetGroupsOutput, lastPage bool) bool {
+			for _, tg := range resp.TargetGroups {
+				for _, v := range allTGARNs {
+					if v != aws.StringValue(tg.TargetGroupArn) {
+						continue
+					}
+					targetTypes[aws.StringValue(tg.TargetType)] = append(targetTypes[aws.StringValue(tg.TargetType)], aws.StringValue(tg.TargetGroupArn))
+				}
+			}
+			return true
+		})
+	log.Debugf("categorized target group arns: %#v", targetTypes)
+	return targetTypes, err
+}
+
 // tgHasTags returns true if the specified resource has the expected tags.
 func tgHasTags(descs []*elbv2.TagDescription, arn string, tags map[string]string) bool {
 	for _, desc := range descs {

aws/asg_test.go

@@ -263,6 +263,7 @@ func TestAttach(t *testing.T) {
 					TargetGroups: []*elbv2.TargetGroup{
 						{
 							TargetGroupArn: aws.String("foo"),
+							TargetType:     aws.String(elbv2.TargetTypeEnumInstance),
 						},
 					},
 				}, nil),
@@ -301,6 +302,7 @@ func TestAttach(t *testing.T) {
 					TargetGroups: []*elbv2.TargetGroup{
 						{
 							TargetGroupArn: aws.String("foo"),
+							TargetType:     aws.String(elbv2.TargetTypeEnumInstance),
 						},
 					},
 				}, nil),
@@ -466,9 +468,11 @@ func TestAttach(t *testing.T) {
 					TargetGroups: []*elbv2.TargetGroup{
 						{
 							TargetGroupArn: aws.String("foo"),
+							TargetType:     aws.String(elbv2.TargetTypeEnumInstance),
 						},
 						{
 							TargetGroupArn: aws.String("bar"),
+							TargetType:     aws.String(elbv2.TargetTypeEnumInstance),
 						},
 					},
 				}, nil),

aws/cf.go

@@ -164,6 +164,7 @@ type stackSpec struct {
 	denyInternalDomainsResponse       denyResp
 	internalDomains                   []string
 	tags                              map[string]string
+	targetAccessModeCNI               bool
 }
 
 type healthCheck struct {

aws/cf_template.go

@@ -8,6 +8,7 @@ import (
 	"crypto/sha256"
 	"sort"
 
+	"github.com/aws/aws-sdk-go/service/elbv2"
 	cloudformation "github.com/mweagle/go-cloudformation"
 )
 
@@ -444,6 +445,10 @@ func generateDenyInternalTrafficRule(listenerName string, rulePriority int64, in
 }
 
 func newTargetGroup(spec *stackSpec, targetPortParameter string) *cloudformation.ElasticLoadBalancingV2TargetGroup {
+	targetType := elbv2.TargetTypeEnumInstance
+	if spec.targetAccessModeCNI {
+		targetType = elbv2.TargetTypeEnumIp
+	}
 	protocol := "HTTP"
 	healthCheckProtocol := "HTTP"
 	healthyThresholdCount, unhealthyThresholdCount := spec.albHealthyThresholdCount, spec.albUnhealthyThresholdCount
@@ -472,6 +477,7 @@ func newTargetGroup(spec *stackSpec, targetPortParameter string) *cloudformation
 		UnhealthyThresholdCount:    cloudformation.Integer(int64(unhealthyThresholdCount)),
 		Port:                       cloudformation.Ref(targetPortParameter).Integer(),
 		Protocol:                   cloudformation.String(protocol),
+		TargetType:                 cloudformation.String(targetType),
 		VPCID:                      cloudformation.Ref(parameterTargetGroupVPCIDParameter).String(),
 	}
 

controller.go

@@ -82,6 +82,8 @@ var (
 	nlbHTTPEnabled                bool
 	ingressAPIVersion             string
 	internalDomains               []string
+	targetAccessMode              string
+	targetCNIPodSelector          string
 	denyInternalDomains           bool
 	denyInternalRespBody          string
 	denyInternalRespContentType   string
@@ -280,13 +282,21 @@ func loadSettings() error {
 		Default("text/plain").StringVar(&denyInternalRespContentType)
 	kingpin.Flag("deny-internal-domains-response-status-code", "Defines the response status code for a request identified as to an internal domain when -deny-internal-domains is set.").
 		Default("401").IntVar(&denyInternalRespStatusCode)
+	kingpin.Flag("target-access-mode", "Target group accessing Ingress via NodePort or AWS VPC CNI. Set to ASG for NodePort access or CNI for pod direct IP access.").
+		Default(aws.TargetAccessModeNodePort).EnumVar(&targetAccessMode, aws.TargetAccessModeNodePort, aws.TargetAccessModeAWSCNI)
+	kingpin.Flag("target-cni-pod-selector", "AWS VPC CNI only. Defines the query (namespace/labelselector) for ingress pods that should be linked to target group. Format 'namespace/key=value'.").
+		Default(aws.DefaultTargetCNILabelSelector).StringVar(&targetCNIPodSelector)
 	kingpin.Parse()
 
 	blacklistCertArnMap = make(map[string]bool)
 	for _, s := range blacklistCertARNs {
 		blacklistCertArnMap[s] = true
 	}
 
+	if sl := strings.SplitN(targetCNIPodSelector, "/", 2); len(sl) != 2 || sl[0] == "" || sl[1] == "" {
+		return fmt.Errorf("Invalid target-cni-pod-selector format")
+	}
+
 	if creationTimeout < 1*time.Minute {
 		return fmt.Errorf("invalid creation timeout %d. please specify a value > 1min", creationTimeout)
 	}
@@ -410,7 +420,8 @@ func main() {
 		WithDenyInternalDomains(denyInternalDomains).
 		WithInternalDomainsDenyResponse(denyInternalRespBody).
 		WithInternalDomainsDenyResponseStatusCode(denyInternalRespStatusCode).
-		WithInternalDomainsDenyResponseContenType(denyInternalRespContentType)
+		WithInternalDomainsDenyResponseContenType(denyInternalRespContentType).
+		WithTargetAccessMode(targetAccessMode)
 
 	log.Debug("certs.NewCachingProvider")
 	certificatesProvider, err := certs.NewCachingProvider(
@@ -444,6 +455,10 @@ func main() {
 	if err != nil {
 		log.Fatal(err)
 	}
+	if err = kubeAdapter.NewInclusterConfigClientset(); err != nil {
+		log.Fatal(err)
+	}
+	kubeAdapter.WithTargetCNIPodSelector(targetCNIPodSelector)
 
 	certificatesPerALB := maxCertsPerALB
 	if disableSNISupport {
@@ -465,10 +480,12 @@ func main() {
 	log.Infof("ALB Logging S3 Prefix: %s", awsAdapter.S3Prefix())
 	log.Infof("CloudWatch Alarm ConfigMap: %s", cwAlarmConfigMapLocation)
 	log.Infof("Default LoadBalancer type: %s", loadBalancerType)
+	log.Infof("Target access mode: %s", targetAccessMode)
 
 	ctx, cancel := context.WithCancel(context.Background())
 	go handleTerminationSignals(cancel, syscall.SIGTERM, syscall.SIGQUIT)
 	go serveMetrics(metricsAddress)
+	go cniEventHandler(ctx, awsAdapter, kubeAdapter)
 	startPolling(
 		ctx,
 		certificatesProvider,

deploy/ingress-serviceaccount.yaml

@@ -13,8 +13,10 @@ rules:
 - apiGroups: # only one of extensions, networking.k8s.io is needed depending on the --ingress-api-version flag
   - extensions
   - networking.k8s.io
+  - ""
   resources:
   - ingresses
+  - pods
   verbs:
   - get
   - list