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Rails Kubernetes Manifests
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"
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
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
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
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
@kwstannard
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kwstannard commented Feb 1, 2022

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.

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