This clustering strategy works by fetching IP addresses with the help of a headless service in current Kubernetes namespace.

This strategy requires exposing pods by a headless service. If you want to avoid that, you could use Cluster.Strategy.Kubernetes.

It assumes that all Erlang nodes are using longnames - <basename>@<ip>:

• all nodes are using the same <basename>
• all nodes are using unique <ip>

In <basename>@<ip>:

• <basename> would be the value configured by :application_name option.
• <ip> would be the value which is controlled by following options:
  • :service
  • :resolver

Getting <basename>

As said above, the basename is configured by :application_name option.

Just one thing to keep in mind - when building an OTP release, make sure that the name of the OTP release matches the name configured by :application_name.

Getting <ip>

It will fetch IP addresses of all pods under a headless service and attempt to connect.

Setup

Getting this strategy to work requires:

1. exposing pod IP from Kubernetes to the Erlang node.
2. setting a headless service for the pods
3. setting the name of Erlang node according to the exposed information

First, expose required information from Kubernetes as environment variables of Erlang node:

# deployment.yaml
env:
- name: POD_IP
  valueFrom:
    fieldRef:
      fieldPath: status.podIP

Second, set a headless service for the pods:

# deployment.yaml
apiVersion: v1
kind: Service
metadata:
  name: myapp-headless
spec:
  selector:
    app: myapp
  type: ClusterIP
  clusterIP: None

Then, set the name of Erlang node by using the exposed environment variables. If you use mix releases, you can configure the required options in rel/env.sh.eex:

# rel/env.sh.eex
export RELEASE_DISTRIBUTION=name
export RELEASE_NODE=<%= @release.name %>@${POD_IP}

Polling Interval

The default interval to sync topologies is 5000 (5 seconds). You can configure it with :polling_interval option.

An example configuration

config :libcluster,
  topologies: [
    erlang_nodes_in_k8s: [
      strategy: Elixir.Cluster.Strategy.Kubernetes.DNS,
      config: [
        service: "myapp-headless",
        application_name: "myapp",
        polling_interval: 10_000
      ]
    ]
  ]