Akka Management

Version 1.6.0

Bootstrap environments

A set of integration tests projects can be found in integration-test folder of the Akka Management project. These test various Akka management features together in various environments such as Kubernetes.

Local

To run Bootstrap locally without any dependencies such as DNS or Kubernetes see the local example

Running Akka Cluster in Kubernetes

The goal of bootstrap is to support running Akka Cluster in Kubernetes as if it is a stateless application. The part bootstrap solves is creating the initial cluster and handling scaling and re-deploys gracefully.

The recommended approach is to:

  • Use a Deployment for creating the pods
  • Use either the Kubernetes API or DNS for contact point discovery (details below)
  • Optionally use a service or ingress for any traffic coming from outside of the Akka Cluster e.g. gRPC and HTTP

Example project

To get started, it might be helpful to have a look at the example projects.

Kubernetes Deployment

Use a regular deployment (not a StatefulSet) with the following settings.

Update strategy

For small clusters it may make sense to set maxUnavailable to 0 and maxSurge to 1. This means that a new pod is created before removing any existing pods so if the new pod fails the cluster remains at full strength until a rollback happens. For large clusters it may be too slow to do 1 pod at a time.

If using Split Brain Resolver have a maxUnavailable that will not cause downing

Cluster singletons

Deployments used to order pods by pod state and then time spent ready when deciding which to remove first. This worked well with cluster singletons as they were typically removed last and then the cluster singletons would move to the oldest new pod. However, since Kubernetes v1.22, this is no longer the default behaviour for Kubernetes deployments thus we advise the use of PodDeletionCost extension from Akka Kubernetes Rolling Update.

External traffic

For production traffic e.g. HTTP use a regular service or an alternative ingress mechanism. With an appropriate readiness check this results in traffic not being routed until bootstrap has finished.

sourceapiVersion: v1
kind: Service
metadata:
  labels:
    app: akka-bootstrap-demo
  name: "integration-test-kubernetes-dns"
spec:
  ports:
  - name: http
    port: 8080
    protocol: TCP
    targetPort: 8080
  selector:
    app: "akka-bootstrap-demo"
  type: LoadBalancer

This will result in a ClusterIP being created and only added to Endpoints when the pods are ready

Note that the app is the same for both services as they both refer to the same pods.

Health checks

akka-management includes a HTTP route for readiness and liveness checks. akka-management-cluster-http includes readiness check for the Akka Cluster membership.

The Akka dependencies are available from Akka’s library repository. To access them there, you need to configure the URL for this repository.

sbt
resolvers += "Akka library repository".at("https://repo.akka.io/maven")
Gradle
repositories {
    mavenCentral()
    maven {
        url "https://repo.akka.io/maven"
    }
}
Maven
<project>
  ...
  <repositories>
    <repository>
      <id>akka-repository</id>
      <name>Akka library repository</name>
      <url>https://repo.akka.io/maven</url>
    </repository>
  </repositories>
</project>

Additionally, add the dependency as below.

sbt
val AkkaManagementVersion = "1.6.0"
libraryDependencies += "com.lightbend.akka.management" %% "akka-management-cluster-http" % AkkaManagementVersion
Gradle
def versions = [
  AkkaManagementVersion: "1.6.0",
  ScalaBinary: "2.13"
]
dependencies {
  implementation "com.lightbend.akka.management:akka-management-cluster-http_${versions.ScalaBinary}:${versions.AkkaManagementVersion}"
}
Maven
<properties>
  <akka.management.version>1.6.0</akka.management.version>
  <scala.binary.version>2.13</scala.binary.version>
</properties>
<dependencies>
  <dependency>
    <groupId>com.lightbend.akka.management</groupId>
    <artifactId>akka-management-cluster-http_${scala.binary.version}</artifactId>
    <version>${akka.management.version}</version>
  </dependency>
</dependencies>

Akka Cluster HTTP Management can be used with Akka 2.10.0 or later. You have to override the following Akka dependencies by defining them explicitly in your build and define the Akka version to the one that you are using. Latest patch version of Akka is recommended and a later version than 2.10.0 can be used.

sbt
val AkkaVersion = "2.10.0"
libraryDependencies ++= Seq(
  "com.typesafe.akka" %% "akka-cluster-sharding" % AkkaVersion,
  "com.typesafe.akka" %% "akka-discovery" % AkkaVersion
)
Gradle
def versions = [
  AkkaVersion: "2.10.0",
  ScalaBinary: "2.13"
]
dependencies {
  implementation "com.typesafe.akka:akka-cluster-sharding_${versions.ScalaBinary}:${versions.AkkaVersion}"
  implementation "com.typesafe.akka:akka-discovery_${versions.ScalaBinary}:${versions.AkkaVersion}"
}
Maven
<properties>
  <akka.version>2.10.0</akka.version>
  <scala.binary.version>2.13</scala.binary.version>
</properties>
<dependencies>
  <dependency>
    <groupId>com.typesafe.akka</groupId>
    <artifactId>akka-cluster-sharding_${scala.binary.version}</artifactId>
    <version>${akka.version}</version>
  </dependency>
  <dependency>
    <groupId>com.typesafe.akka</groupId>
    <artifactId>akka-discovery_${scala.binary.version}</artifactId>
    <version>${akka.version}</version>
  </dependency>
</dependencies>

The readiness check is exposed on the Akka Management port as a GET on /ready and the liveness check is a GET on /alive

Configure them to be used in your deployment:

sourcereadinessProbe:
  httpGet:
    path: /ready
    port: management
livenessProbe:
  httpGet:
    path: /alive
    port: management

This will mean that a pod won’t get traffic until it is part of a cluster, which is important if either ClusterSharding or ClusterSingleton are used.

Contact point discovery

Contact point discovery can use either kubernetes or akka-dns service discovery. Details on additional resources required and how they work:

Kubernetes-api is the more battle tested mechanism, DNS was added in Akka 2.5.15 and Akka Management 0.18. DNS has the benefit that it is agnostic of Kubernetes so does not require pods be able to communicate with the API server. However it requires a headless service that supports the publishNotReadyAddresses feature. If your Kubernetes setup does not support publishNotReadyAddresses yet then use the kubernetes-api discovery mechanism.

Running in Istio

For considerations and configuration necessary for bootstrapping an Akka cluster in Istio, see Bootstrapping an Akka cluster in Istio.

Running the Kubernetes demos

The following steps work for the integration-test/kubernetes-api or the integration-test/kubernetes-dns sub-project:

To run the demo in a real Kubernetes or OpenShift cluster the images must be pushed to a registry that cluster has access to and then kubernetes/akka-cluster.yml (in either sub-project) modified with the full image path.

The following shows how the sample can be run in a local cluster using either minishift or minikube. Unless explicitly stated minikube can be replaced with minishift and kubectl with oc in any of the commands below.

Start minikube make sure you have installed and is running:

$ minikube start

Make sure your shell is configured to target the docker daemon running inside the VM:

$ eval $(minikube docker-env)

Publish the application docker image locally. If running this project in a real cluster you’ll need to publish the image to a repository that is accessible from your Kubernetes cluster and update the kubernetes/akka-cluster.yml with the new image name.

$ sbt shell
> project integration-test-kubernetes-api (or integration-test-kubernetes-dns)
> docker:publishLocal

You can run multiple different Akka Bootstrap-based applications in the same namespace, alongside any other containers that belong to the same logical application. The resources in kubernetes/akka-cluster.yml are configured to run in the akka-bootstrap-demo-ns namespace. Change that to the namespace you want to deploy to. If you do not have a namespace to run your application in yet, create it:

kubectl create namespace <insert-namespace-name-here>

# and set it as the default for subsequent commands
kubectl config set-context $(kubectl config current-context) --namespace=<insert-namespace-name-here>

Or if running with minishift:

oc new-project <insert-namespace-name-here>

# and switch to that project to make it the default for subsequent comments
oc project <insert-namespace-name-here>

Next deploy the application:

# minikube using Kubernetes API
kubectl apply -f integration-test/kubernetes-api/kubernetes/akka-cluster.yml

or

# minikube using DNS
kubectl apply -f integration-test/kubernetes-dns/kubernetes/akka-cluster.yml

or

# minishift using Kubernetes API
oc apply -f integration-test/kubernetes-api/kubernetes/akka-cluster.yaml

or

# minishift using DNS
oc apply -f integration-test/kubernetes-dns/kubernetes/akka-cluster.yaml

This will create and start running a number of Pods hosting the application. The application nodes will form a cluster.

In order to observe the logs during the cluster formation you can pick one of the pods and issue the kubectl logs command on it:

$ POD=$(kubectl get pods | grep akka-bootstrap | grep Running | head -n1 | awk '{ print $1 }'); echo $POD
akka-integration-test-bcc456d8c-6qx87

$ kubectl logs $POD --follow | less

[INFO] [12/13/2018 07:13:42.867] [main] [ClusterBootstrap(akka://default)] Initiating bootstrap procedure using akka.discovery.akka-dns method...
[DEBUG] [12/13/2018 07:13:42.906] [default-akka.actor.default-dispatcher-2] [TimerScheduler(akka://default)] Start timer [resolve-key] with generation [1]
[DEBUG] [12/13/2018 07:13:42.919] [default-akka.actor.default-dispatcher-2] [TimerScheduler(akka://default)] Start timer [decide-key] with generation [2]
[INFO] [12/13/2018 07:13:42.924] [default-akka.actor.default-dispatcher-2] [akka.tcp://[email protected]:2552/system/bootstrapCoordinator] Locating service members. Using discovery [akka.discovery.dns.DnsSimpleServiceDiscovery], join decider [akka.management.cluster.bootstrap.LowestAddressJoinDecider]
[INFO] [12/13/2018 07:13:42.933] [default-akka.actor.default-dispatcher-2] [akka.tcp://[email protected]:2552/system/bootstrapCoordinator] Looking up [Lookup(integration-test-kubernetes-dns-internal.akka-bootstrap.svc.cluster.local,Some(management),Some(tcp))]
[DEBUG] [12/13/2018 07:13:42.936] [default-akka.actor.default-dispatcher-2] [DnsSimpleServiceDiscovery(akka://default)] Lookup [Lookup(integration-test-kubernetes-dns-internal.akka-bootstrap-demo-ns.svc.cluster.local,Some(management),Some(tcp))] translated to SRV query [_management._tcp.integration-test-kubernetes-dns-internal.akka-bootstrap-demo-ns.svc.cluster.local] as contains portName and protocol
[DEBUG] [12/13/2018 07:13:42.995] [default-akka.actor.default-dispatcher-18] [akka.tcp://[email protected]:2552/system/IO-DNS] Resolution request for _management._tcp.integration-test-kubernetes-dns-internal.akka-bootstrap-demo-ns.svc.cluster.local Srv from Actor[akka://default/temp/$a]
[DEBUG] [12/13/2018 07:13:43.011] [default-akka.actor.default-dispatcher-6] [akka.tcp://[email protected]:2552/system/IO-DNS/async-dns/$a] Attempting to resolve _management._tcp.integration-test-kubernetes-dns-internal.akka-bootstrap-demo-ns.svc.cluster.local with Actor[akka://default/system/IO-DNS/async-dns/$a/$a#1272991285]
[DEBUG] [12/13/2018 07:13:43.049] [default-akka.actor.default-dispatcher-18] [akka.tcp://[email protected]:2552/system/IO-TCP/selectors/$a/0] Successfully bound to /0.0.0.0:8558
[DEBUG] [12/13/2018 07:13:43.134] [default-akka.actor.default-dispatcher-18] [akka.tcp://[email protected]:2552/system/IO-DNS/async-dns/$a/$a] Resolving [_management._tcp.integration-test-kubernetes-dns-internal.akka-bootstrap-demo-ns.svc.cluster.local] (SRV)
[INFO] [12/13/2018 07:13:43.147] [default-akka.actor.default-dispatcher-6] [AkkaManagement(akka://default)] Bound Akka Management (HTTP) endpoint to: 0.0.0.0:8558
[DEBUG] [12/13/2018 07:13:43.156] [default-akka.actor.default-dispatcher-5] [akka.tcp://[email protected]:2552/system/IO-TCP/selectors/$a/1] Successfully bound to /0.0.0.0:8080
[INFO] [12/13/2018 07:13:43.180] [main] [akka.actor.ActorSystemImpl(default)] Server online at http://localhost:8080/
....
[INFO] [12/13/2018 07:13:50.631] [default-akka.actor.default-dispatcher-5] [akka.cluster.Cluster(akka://default)] Cluster Node [akka.tcp://[email protected]:2552] - Welcome from [akka.tcp://[email protected]:2552]
[DEBUG] [12/13/2018 07:13:50.644] [default-akka.remote.default-remote-dispatcher-22] [akka.serialization.Serialization(akka://default)] Using serializer [akka.cluster.protobuf.ClusterMessageSerializer] for message [akka.cluster.GossipEnvelope]
[INFO] [12/13/2018 07:13:50.659] [default-akka.actor.default-dispatcher-18] [akka.tcp://[email protected]:2552/user/$b] Cluster akka.tcp://[email protected]:2552 >>> MemberUp(Member(address = akka.tcp://[email protected]:2552, status = Up))
[INFO] [12/13/2018 07:13:50.676] [default-akka.actor.default-dispatcher-20] [akka.tcp://[email protected]:2552/user/$b] Cluster akka.tcp://[email protected]:2552 >>> MemberJoined(Member(address = akka.tcp://[email protected]:2552, status = Joining))
[INFO] [12/13/2018 07:13:50.716] [default-akka.actor.default-dispatcher-6] [akka.tcp://[email protected]:2552/user/$b] Cluster akka.tcp://[email protected]:2552 >>> LeaderChanged(Some(akka.tcp://[email protected]:2552))
[INFO] [12/13/2018 07:13:50.720] [default-akka.actor.default-dispatcher-3] [akka.tcp://[email protected]:2552/user/$b] Cluster akka.tcp://[email protected]:2552 >>> RoleLeaderChanged(dc-default,Some(akka.tcp://[email protected]:2552))
[INFO] [12/13/2018 07:13:50.727] [default-akka.actor.default-dispatcher-6] [akka.tcp://[email protected]:2552/user/$b] Cluster akka.tcp://[email protected]:2552 >>> SeenChanged(true,Set(akka.tcp://[email protected]:2552, akka.tcp://[email protected]:2552))
[INFO] [12/13/2018 07:13:50.733] [default-akka.actor.default-dispatcher-5] [akka.tcp://[email protected]:2552/user/$b] Cluster akka.tcp://[email protected]:2552 >>> ReachabilityChanged()
Akka Cluster Bootstrap
Bootstrap process
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