The purpose of this project is to provide an easy way to run akka cluster applications on kubernetes.
Current version: 1.0.1
build.sbt
libraryDependencies += "de.aktey.akka.k8s" %% "seednode-config" % "1.0.1"You start your application on a dynamically assigned node. So you cannot know the seed nodes IP addresses, which needs to be configured at startup for akka cluster.
Kubernetes offers an API to look up the IP of a service. The endpoint of the API can be derived from environment variables, set by kubernetes.
de.aktey.akka.k8s.SeednodeConfig asks the API for its service IPs, takes the
first five elements and configures a com.typesafe.config.Config object for an
akka cluster. The concrete name spaces, that are set are:
akka.remote.netty.tcp.hostnameakka.cluster.seed-nodes
If no service IP is found (because no k8s service for a pod is started yet),
de.aktey.akka.k8s.SeednodeConfig#getConfig will throw an exception, so the
container can fail fast. The first container up, will see only one seed IP
(its own) and will assume itself the cluster leader.
Akka doesn't seem to be designed for dynamic node assignment see auto-downing section. So it seems to be a good advice to have a closer look at the warning box in that chapter.
- As this is a base library, it should not introduce more any dependencies
(#nodependencies). So
this library uses only dependencies, that are already there by its nature:
- scala
- typesafe config (introduced by akka)
- fail fast
import akka.actor._
import com.typesafe.config.ConfigFactory
import de.aktey.akka.k8s.SeednodeConfig
object Main extends App {
val systemName = "akka-k8s"
// create the seed node config
val kubeConfig = K8sSeednodeConfig.getConfig(systemName)
// load the rest of the config
// resolve the variables introduced by `K8sSeednodeConfig.getConfig`
val config = kubeConfig.withFallback(ConfigFactory.load()).resolve()
// start the cluster node
val system = ActorSystem(systemName, config)
println(s"running : ")
}Have a look at the example project. You can use it right away after building it with sbt docker:publishLocal.
Then you can use the kubernetes definition files in seednode-config-example/src/k8s to run
the example.
akka-k8s-seednode> kubectl create -f seednode-config-example/src/k8s
replicationcontroller "akka-k8s-example" created
service "akka-k8s-example" created
akka-k8s-seednode> kubectl get svc
NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE
akka-k8s-example 10.0.0.121 <nodes> 8080/TCP,2552/TCP 8s
kubernetes 10.0.0.1 <none> 443/TCP 5d
akka-k8s-seednode> kubectl get rc
NAME DESIRED CURRENT AGE
akka-k8s-example 1 1 18s
akka-k8s-seednode> kubectl get pod
NAME READY STATUS RESTARTS AGE
akka-k8s-example-ztehd 1/1 Running 0 21s
akka-k8s-seednode> kubectl scale rc akka-k8s-example --replicas=3
replicationcontroller "akka-k8s-example" scaled
akka-k8s-seednode> kubectl get pod
NAME READY STATUS RESTARTS AGE
akka-k8s-example-ge388 1/1 Running 0 2s
akka-k8s-example-q87dn 1/1 Running 0 2s
akka-k8s-example-ztehd 1/1 Running 0 31s
akka-k8s-seednode> kubectl logs akka-k8s-example-ztehd
[...]
08:37:19.222 [akka-k8s-akka.actor.default-dispatcher-18] INFO a.cluster.Cluster(akka://akka-k8s) - Cluster Node [akka.tcp://[email protected]:2552] - Node [akka.tcp://[email protected]:2552] is JOINING, roles []
08:37:19.233 [akka-k8s-akka.actor.default-dispatcher-4] INFO a.cluster.Cluster(akka://akka-k8s) - Cluster Node [akka.tcp://[email protected]:2552] - Leader is moving node [akka.tcp://[email protected]:2552] to [Up]
08:37:51.301 [akka-k8s-akka.actor.default-dispatcher-5] DEBUG akka.remote.Remoting - Associated [akka.tcp://[email protected]:2552] <- [akka.tcp://[email protected]:2552]
08:37:51.594 [akka-k8s-akka.actor.default-dispatcher-5] DEBUG akka.remote.Remoting - Associated [akka.tcp://[email protected]:2552] <- [akka.tcp://[email protected]:2552]
08:37:51.700 [akka-k8s-akka.actor.default-dispatcher-5] INFO a.cluster.Cluster(akka://akka-k8s) - Cluster Node [akka.tcp://[email protected]:2552] - Node [akka.tcp://[email protected]:2552] is JOINING, roles []
08:37:51.859 [akka-k8s-akka.actor.default-dispatcher-3] INFO a.cluster.Cluster(akka://akka-k8s) - Cluster Node [akka.tcp://[email protected]:2552] - Node [akka.tcp://[email protected]:2552] is JOINING, roles []
08:37:52.181 [akka-k8s-akka.actor.default-dispatcher-6] INFO a.cluster.Cluster(akka://akka-k8s) - Cluster Node [akka.tcp://[email protected]:2552] - Leader is moving node [akka.tcp://[email protected]:2552] to [Up]
08:37:52.189 [akka-k8s-akka.actor.default-dispatcher-6] INFO a.cluster.Cluster(akka://akka-k8s) - Cluster Node [akka.tcp://[email protected]:2552] - Leader is moving node [akka.tcp://[email protected]:2552] to [Up]
[...]