View Source FlameK8sBackend

A FLAME Backend for Kubernetes. Manages pods as runners in the cluster the app is running in.

The current implementation is very basic and more like a proof of concept. More configuration options (resources, etc.) will follow.

Installation

def deps do
  [
    {:flame_k8s_backend, "~> 0.1.0"}
  ]
end

Requirements

Env Variables

In order for the runners to be able to join the cluster, you need to configure a few environment variables on your pod/deployment:

The POD_NAME and POD_NAMESPACE are used by the backend to get informations from your pod and use them for the runner pods (e.g. env variables).

apiVersion: apps/v1
kind: Deployment
spec:
  selector:
    matchLabels:
      app: myapp
  template:
    spec:
      metadata:
        excluster: flame # see note in the headless service section below
        app: myapp
      containers:
        - env:
            - name: POD_NAME
              valueFrom:
                fieldRef:
                  apiVersion: v1
                  fieldPath: metadata.name
            - name: POD_NAMESPACE
              valueFrom:
                fieldRef:
                  apiVersion: v1
                  fieldPath: metadata.namespace

RBAC

Your application needs run as a service account with permissions to manage pods:

---
apiVersion: v1
kind: ServiceAccount
metadata:
  name: myapp
  namespace: michael-playground
---
apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  namespace: michael-playground
  name: pod-mgr
rules:
  - apiGroups: [""]
    resources: ["pods"]
    verbs: ["create", "get", "list", "delete", "patch"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  name: myapp-pod-mgr
  namespace: michael-playground
subjects:
  - kind: ServiceAccount
    name: myapp
    namespace: michael-playground
roleRef:
  kind: Role
  name: pod-mgr
  apiGroup: rbac.authorization.k8s.io
---
apiVersion: apps/v1
kind: Deployment
spec:
  template:
    spec:
      serviceAccountName: flame-test

Clustering

Your application needs to be able to form a cluster with your runners. One way to achieve this is to use DNSCluster.

ENV Variables

Pass the following variables to your pods

apiVersion: apps/v1
kind: Deployment
spec:
  template:
    spec:
      containers:
        - env:
            - name: POD_IP
              valueFrom:
                fieldRef:
                  apiVersion: v1
                  fieldPath: status.podIP
            - name: RELEASE_DISTRIBUTION
              value: name
            - name: RELEASE_NODE
              value: flame_test@$(POD_IP)

Headless Service

A headless service tells DNSCluster the IP addresses of the runner pods.

NOTE: The selector you use on the service should NOT be the same label you're using for the Replicaset of your deployment. Otherwise the Replicaset controller is going to see your runner pods as additional replicas of your application and immetiately terminate them!

---
apiVersion: v1
kind: Service
metadata:
  name: myapp-headless
  namespace: michael-playground
spec:
  selector:
    excluster: flame
  type: ClusterIP
  clusterIP: None

DNSCluster Setup

defmodule MyApp.Application do
  @moduledoc false

  use Application

  @impl true
  def start(_type, _opts) do
    children =
      [
        # other children

        # use the name of the headless service above for query
        {DNSCluster, query: "myapp-headless", log: :debug}
      ]

    Supervisor.start_link(children,
      strategy: :one_for_one,
      name: KinoK8s.Supervisor
    )
  end