libcluster v3.0.3 Cluster.Strategy.Kubernetes

This clustering strategy works by loading all endpoints in the current Kubernetes namespace with the configured label. It will fetch the addresses of all endpoints with that label and attempt to connect. It will continually monitor and update its connections every 5s.

In order for your endpoints to be found they should be returned when you run:

kubectl get endpoints -l app=myapp

It assumes that all nodes share a base name, are using longnames, and are unique based on their FQDN, rather than the base hostname. In other words, in the following longname, <basename>@<domain>, basename would be the value configured in kubernetes_node_basename.

domain would be the value configured in mode and can be either of type :ip (the pod’s ip, can be obtained by setting an env variable to status.podIP) or :dns, which is the pod’s internal A Record. This A Record has the format <ip-with-dashes>.<namespace>.pod.cluster.local, e.g 1-2-3-4.default.pod.cluster.local.

Getting :dns to work requires a bit fiddling in the container’s CMD, for example:

# deployment.yaml
command: ["sh", "-c"]
args: ["POD_A_RECORD"]
args: ["export POD_A_RECORD=$(echo $POD_IP | sed 's/./-/g') && /app/bin/app foreground"]

# vm.args
-name app@<%= "${POD_A_RECORD}.${NAMESPACE}.pod.cluster.local" %>

(in an app running as a Distillery release).

The benefit of using :dns over :ip is that you can establish a remote shell (as well as run observer) by using kubectl port-forward in combination with some entries in /etc/hosts.

Defaults to :ip.

An example configuration is below:

config :libcluster,
  topologies: [
    k8s_example: [
      strategy: Elixir.Cluster.Strategy.Kubernetes,
      config: [
        mode: :ip,
        kubernetes_node_basename: "myapp",
        kubernetes_selector: "app=myapp",
        polling_interval: 10_000]]]

Link to this section Summary

Functions

Returns a specification to start this module under a supervisor

Callback implementation for Cluster.Strategy.start_link/1

Link to this section Functions

Link to this function child_spec(arg)

Returns a specification to start this module under a supervisor.

See Supervisor.

Link to this function start_link(args)

Callback implementation for Cluster.Strategy.start_link/1.