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Constructr-coordination-demo

Akka Cluster demo using Constructr-Consul.

Usage

Prerequisites

Make sure you have already installed both Docker Engine and Docker Compose.

Steps

  • Seed node in Docker: sbt constructr-coordination-demo/docker:publishLocal
  • Remove docker containers (if exist): docker rm -f consul1 consul2 akka_node1 akka_node2 akka_node3
  • Run the application: docker-compose -f constructr-coordination-demo/docker-compose.yml up

We should see something like this:

Starting consul1
Starting consul2
Starting akka_node3
Starting akka_node1
Starting akka_node2
...
consul1       | ==> Starting Consul agent...
consul2       | ==> Starting Consul agent...
...
consul1       |     2016/06/01 15:44:14 [INFO] consul: member 'consul2' joined, marking health alive
consul2       |     2016/06/01 15:44:16 [INFO] agent: Synced node info
...
akka_node3    | 15:44:17 INFO  Constructr [akka.tcp://ConstructR-Consul@172.18.0.4:2552/system/constructr] - Creating constructr-machine, because no seed-nodes defined
akka_node3    | 15:44:17 DEBUG ConstructrMachine [akka.tcp://ConstructR-Consul@172.18.0.4:2552/system/constructr/constructr-machine] - Transitioning to GettingNodes
akka_node2    | 15:44:17 INFO  Constructr [akka.tcp://ConstructR-Consul@172.18.0.5:2552/system/constructr] - Creating constructr-machine, because no seed-nodes defined
akka_node1    | 15:44:17 INFO  Constructr [akka.tcp://ConstructR-Consul@172.18.0.6:2552/system/constructr] - Creating constructr-machine, because no seed-nodes defined
akka_node2    | 15:44:17 DEBUG ConstructrMachine [akka.tcp://ConstructR-Consul@172.18.0.5:2552/system/constructr/constructr-machine] - Transitioning to GettingNodes
akka_node1    | 15:44:17 DEBUG ConstructrMachine [akka.tcp://ConstructR-Consul@172.18.0.6:2552/system/constructr/constructr-machine] - Transitioning to GettingNodes
  • Consul UI: http://localhost:8500/ui/

You can use Consul UI for checking services, nodes, reading/writing key/value data, view/invalidate sessions.

HTTP API

  • Consul:

    • Check nodes: curl "http://localhost:8500/v1/kv/constructr/ConstructR-Consul/nodes/?recurse&pretty"

      List node key/value pairs

    • Active sessions: curl http://localhost:8500/v1/session/list?pretty

      List active sessions attached to consul nodes

    • Delete session: curl -XPUT http://localhost:8500/v1/session/destroy/{session-id}

      If you delete a session, Constructr-Consul will create a new one.

  • Akka:

    • Get the member nodes: curl 127.0.0.1:8000/member-nodes.

    We can check the akka members in the cluster here (if everything is working properly, we should see this):

    akka.tcp://ConstructR-Consul@172.18.0.4:2552
akka.tcp://ConstructR-Consul@172.18.0.5:2552
akka.tcp://ConstructR-Consul@172.18.0.6:2552

Configuration

constructr {
  // We need to configure the agent name under which sessions will be saved
  // This property will be typically set by a cluster scheduler service as could be Nomad or Kubernetes.
  consul.agent-name = "consul2"
  consul.access-token = "token"
}

In a production environment, you should launch both the consul agent and the akka system together on the same machine configuring the consul.agent-name property according to the host name or ip address, so that if the machine crashes then the consul session can be properly invalidated.