akka-sample-cluster-kubernetes-scala

akka sample cluster with kubernetes discovery in scala

This is an example SBT project showing how to create an Akka Cluster on Kubernetes using Istio.

It is not always necessary to use Akka Cluster when deploying an Akka application to Kubernetes: if your application can be designed as independent stateless services that do not need coordination, deploying them on Kubernetes as individual Akka application without Akka Cluster can be a good fit. When state or coordination between nodes is necessary, this is where the Akka Cluster features become interesting and it is worth consider making the nodes form an Akka Cluster.

Kubernetes Instructions

Starting

First, package the application and make it available locally as a docker image:

sbt docker:publishLocal

Now push it to any registry accessable from cluster - current configuration is using dockerHub

Then akka-cluster.yaml should be sufficient to deploy a 3-node Akka Cluster

kubectl apply -f kubernetes/akka-cluster.yaml

There are 2 ways to make it work with Istio 1.5.x and above:

• Add port 443 to the excluded outbound ports akka-cluster-443
• Add API server to the excluded outbond IPs akka-cluster. To find the IP of the API server (used here) run kubectl get svc kubernetes -o jsonpath='{.spec.clusterIP}'

To test application you can use port forward. To see configuration, use port 8558:

kubectl port-forward <pod name> 8558

Now you can inspect the Akka Cluster membership status with the Cluster HTTP Management.

curl http://localhost:8558/cluster/members/

Alternatively you can expose port 8080

kubectl port-forward <pod name> 8558

and run

curl http://localhost:8080

To wipe everything clean and start over, do:

kubectl delete deployment appka

How it works

This example uses Akka Cluster Bootstrap to initialize the cluster, using the Kubernetes API discovery mechanism to find peer nodes.