akka-zk-cluster-seed

Bootstrap your akka cluster with this one simple trick.

akka-zk-cluster-seed is an akka extension that will free you from having to manage cluster seed nodes.

Assuming you already have easy access to a zookeeper cluster.

use

Add the folowing dependency to your project. akka-zk-cluster-seed is built with akka dependencies marked as provided, so it should work with a reasonable range of akka versions configured in your build.sbt. Note that you must also have `spray 1.3.X and spray-json as dependencies in your project if you want to use the neftlix exhibitor integration described below.

libraryDependencies += "com.sclasen" %% "akka-zk-cluster-seed" % "0.1.2"  // If using Akka 2.3.x
libraryDependencies += "com.sclasen" %% "akka-zk-cluster-seed" % "0.1.8"  // If using Akka 2.4.x

When starting your app, use the ZookeeperClusterSeed extension, instead of the Cluster extension to join your cluster.

val system = ...
ZookeeperClusterSeed(system).join()

configure

akka-zk-cluster-seed uses the standard akka reference.conf configuration defaults mechanism.

You will certainly want to provide an override to the akka.cluster.seed.zookeeper.url config property. It expects standard zookeeper url format like so: 192.168.12.11,192.168.12.12,192.168.12.13:2818

// reference.conf
akka.cluster.seed.zookeeper {
    url = "127.0.0.1:2181"
    path = "/akka/cluster/seed"
}

netfix exhibitor integration: if you want to use netflix exhibitor to discover your zookeeper servers, you should configure like so.

// application.conf
akka.cluster.seed.zookeeper {
    path = "/akka/cluster/seed"
    exhibitor {
        url = "https://user:pass@host:port
        validate-certs = true|false
    }
}

If you require a different exhibitor request path than the default /exhibitor/v1/cluster/list

// application.conf
akka.cluster.seed.zookeeper {
    path = "/akka/cluster/seed"
    exhibitor {
        url = "https://user:pass@host:port
        request-path = "/my/custom/path"
        validate-certs = true|false
    }
}

If your zookeeper path requires authorization you have to specify additional authorization section:

// application.conf
akka.cluster.seed.zookeeper {
    authorization {
        scheme = "digest"
        auth = "username:secret"
    }
}

details

akka-zk-cluster-seed uses netflix curator zookeeper client and recipes to manage a single, dynamic seed node for your cluster. It uses the curator LeaderLatch to elect a node to serve as a seed node. The lead node joins itself to the cluster and all other nodes joinSeedNodes using the current leader as the seed. If the leader goes offline, a new leader is elected to be the seed.

If you need to use other hostname & port you may configure the name of the environment variables to retrieve these values from. This might be handy to use with docker containers

// reference.conf
akka.cluster.seed.zookeeper {
    url = "127.0.0.1:2181"
    path = "/akka/cluster/seed"
    host_env_var = ${?HOST}
    port_env_var = ${?PORT_8080}
}