DevOps Classroom notes 29/Jun/2026

Pods

• Pods will have different types of containers
  • init containers: for initialization or checks
  • main application(main car)
  • side car containers
  • ephemeral containers
• Pod life cycle

• Pod will
  • first create init containers one by one
  • once the init containers finish then the
  • main car and side car containers are created in parallel
• A container generally when running will launch CMD or ENTRYPOINT and if this command returns 0 (success) any thing else (FAILURE)

Lets write some examples

• 2 init containers with sleep 5 seconds
• main container with nginx

apiVersion: v1
kind: Pod
metadata:
  name: ex-1
spec:
  initContainers:
    - name: init1
      image: alpine
      command: 
        - sleep 
        - "5"
    - name: init2
      image: alpine
      command: 
        - sleep 
        - "5"
  containers:
    - name: web
      image: nginx

• Lets try running one main car and one side car container with two init contaienrs

apiVersion: v1
kind: Pod
metadata:
  name: ex-2
spec:
  initContainers:
    - name: init1
      image: alpine
      command: 
        - sleep 
        - "5"
    - name: init2
      image: alpine
      command: 
        - sleep 
        - "5"
  containers:
    - name: web
      image: nginx
    - name: logger
      image: alpine
      command:
        - sleep
        - "1d"

• init containers failing will not start main container
• what if main container is failing

apiVersion: v1
kind: Pod
metadata:
  name: ex-3
spec:
  initContainers:
    - name: init1
      image: alpine
      command: 
        - sleep 
        - "5"
    - name: init2
      image: alpine
      command: 
        - sleep 
        - "5"
  containers:
    - name: web
      image: alpine
      command:
        - sleep
        - "3s"
    - name: logger
      image: alpine
      command:
        - sleep
        - "1d"

• This will lead to CrashLoopBackoff
  
• To create a sidecar containers in newer versions of k8s add restart: always in init-contianers Refer Here

Health Probes

• We can define health probes Refer Here
• There are three types of probes
  • Startup probes
  • Readiness Probes
  • Liveness Probes
• Prompt:

Create a simple tabular summary of health probes and impact of what happens when they fail or succed refer https://kubernetes.io/docs/concepts/workloads/pods/probes/

• To write a probe

Give me an example of writing different types of probes
    * command based 
    * request based

Give me a simple pod with one container based examples for each probe type