pod_again.md

Pod - Deep Dive

Run a pod with 2 containers

Init container

• Great for initialization needed before starting the apps

• Init container does not live beyond the initialization process

• Can have more than one init container

• Following pod will not start until the two endpoints are reachable

apiVersion: v1
kind: Pod
metadata:
  name: myapp-pod
  labels:
    app: myapp
spec:
  containers:
  - name: myapp-container
    image: busybox
    command: ['sh', '-c', 'echo The app is running! && sleep 3600']
  initContainers:
  - name: init-myservice
    image: busybox
    command: ['sh', '-c', 'until nslookup myservice; do echo waiting for myservice; sleep 2; done;']
  - name: init-mydb
    image: busybox
    command: ['sh', '-c', 'until nslookup mydb; do echo waiting for mydb; sleep 2; done;']

And the services which will enable above pod's initialization process:

kind: Service
apiVersion: v1
metadata:
  name: myservice
spec:
  ports:
  - protocol: TCP
    port: 80
    targetPort: 9376
---
kind: Service
apiVersion: v1
metadata:
  name: mydb
spec:
  ports:
  - protocol: TCP
    port: 80
    targetPort: 9377

• Use cases
  • Initialization of a secret/auth data from external service
  • Checking an external system is up before starting etc.

Pod Termination - grace period

• Pre termination hooks allow to cleanup/persist state before exiting

Health Checks

• Demo app - probes_app scenarios

Readiness Probe

Liveness Probe

Restart policies

Three restart policies:

• Always
• OnFailure
• Never

Resource allocation

• Requests

• Limits

Volumes - Quick overview