Rails Kubernetes Manifests

configmap.yaml

apiVersion: v1
kind: ConfigMap
metadata:
  name: example
  namespace: default
data:
  APPLICATION_HOST: example.com
  LANG: en_US.UTF-8
  PIDFILE: /tmp/server.pid
  PORT: "3000"
  RACK_ENV: production
  RAILS_ENV: production
  RAILS_LOG_TO_STDOUT: "true"
  RAILS_SERVE_STATIC_FILES: "true"

db-migrate.yaml

apiVersion: batch/v1
kind: Job
metadata:
  generateName: db-migrate-
  labels:
    app.kubernetes.io/name: example
  namespace: default
spec:
  template:
    metadata:
      labels:
        app.kubernetes.io/name: example
    spec:
      containers:
      - command:
        - rails
        - db:migrate
        envFrom:
        - configMapRef:
            name: env
        - secretRef:
            name: env
        image: docker.io/mycompany/myapplication:abcd123
        imagePullPolicy: IfNotPresent
        name: main
      restartPolicy: Never

deployment.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app.kubernetes.io/name: example
    process: web
  name: example-web
  namespace: default
spec:
  selector:
    matchLabels:
      app.kubernetes.io/name: example
      process: web
  template:
    metadata:
      labels:
        app.kubernetes.io/name: example
        process: web
    spec:
      containers:
      - env:
        - name: PORT
          value: "3000"
        envFrom:
        - configMapRef:
            name: example
        - secretRef:
            name: example
        image: docker.io/mycompany/myapplication:abcd123
        imagePullPolicy: IfNotPresent
        name: main
        ports:
        - containerPort: 3000
          name: http
          protocol: TCP
        readinessProbe:
          httpGet:
            httpHeaders:
            - name: Host
              value: example.com
            path: /robots.txt
            port: 3000
          initialDelaySeconds: 10
          periodSeconds: 10
          timeoutSeconds: 2
      initContainers:
      - command:
        - rake
        - db:abort_if_pending_migrations
        envFrom:
        - configMapRef:
            name: example
        - secretRef:
            name: example
        image: docker.io/mycompany/myapplication:abcd123
        imagePullPolicy: IfNotPresent
        name: migrations

ingress.yaml

apiVersion: networking.k8s.io/v1beta1
kind: Ingress
metadata:
  labels:
    app.kubernetes.io/name: example
  name: example
  namespace: default
spec:
  rules:
  - host: example.com
    http:
      paths:
      - backend:
          serviceName: example-web
          servicePort: 3000
  tls:
  - hosts:
    - example.com
    secretName: example-tls

service.yaml

apiVersion: v1
kind: Service
metadata:
  labels:
    app.kubernetes.io/name: example
    process: web
  name: example-web
  namespace: default
spec:
  ports:
  - name: http
    port: 3000
    protocol: TCP
    targetPort: http
  selector:
    app.kubernetes.io/name: example
    process: web
  type: ClusterIP

To improve the speed of this, create a route specifically for the readinessProbe or even better, use a startupProbe (I am using the health_check gem). That route should, among other things, return 500 if migrations are pending. Then you can get rid of the initContainer. What will then happen is the app pods will start concurrently with the migration job and sit there returning 500's to k8s until the migrations finish, at which point they will return 200 and k8s will mark them as ready for traffic. This will cut deployment time in more than half compared to initContainers.