💡 Quick Answer: configuration

The Problem

This is one of the most searched Kubernetes topics with thousands of monthly searches. A comprehensive, production-ready guide prevents hours of trial and error.

The Solution

Pod Phases

Phase	Meaning
Pending	Accepted but not running (downloading image, waiting for node)
Running	At least one container running
Succeeded	All containers exited with code 0
Failed	At least one container exited with non-zero
Unknown	Cannot determine state (node communication lost)

Container States

kubectl describe pod my-pod
# State:          Running
#   Started:      Mon, 07 Apr 2026 10:00:00 UTC
# Last State:     Terminated
#   Reason:       OOMKilled
#   Exit Code:    137

State	Description
`Waiting`	Not yet running (pulling image, waiting for deps)
`Running`	Container executing
`Terminated`	Finished execution (success or failure)

Pod Lifecycle Timeline

1. Pod created → API server stores in etcd
2. Scheduler assigns to node
3. kubelet pulls images
4. Init containers run (sequentially)
5. postStart hook (if defined)
6. Main containers start
7. Startup probe (if defined)
8. Liveness + Readiness probes begin
9. Pod runs...
10. Deletion requested
11. Pod removed from Service endpoints
12. preStop hook runs
13. SIGTERM sent to containers
14. terminationGracePeriodSeconds countdown
15. SIGKILL if still running
16. Pod removed from API

Lifecycle Hooks

spec:
  containers:
    - name: app
      lifecycle:
        postStart:
          exec:
            command: ["/bin/sh", "-c", "echo started > /tmp/started"]
          # Or httpGet:
          #   path: /started
          #   port: 8080
        preStop:
          exec:
            command: ["sh", "-c", "sleep 5 && /app/shutdown.sh"]

graph TD
    A[Pod Created] --> B[Pending: scheduled to node]
    B --> C[Init containers run sequentially]
    C --> D[postStart hook]
    D --> E[Running: main containers start]
    E --> F[Probes: startup → liveness + readiness]
    F --> G[Pod serves traffic]
    G --> H[Deletion requested]
    H --> I[Removed from Service endpoints]
    I --> J[preStop hook]
    J --> K[SIGTERM]
    K -->|Grace period| L[SIGKILL if needed]
    L --> M[Pod terminated]

Frequently Asked Questions

postStart vs init container?

Init containers run BEFORE main containers start (separate container, guaranteed ordering). postStart runs inside the main container, concurrently with the entrypoint — no ordering guarantee. Use init containers for setup tasks.

What’s exit code 137?

128 + 9 = SIGKILL. The container was forcefully killed — either OOMKilled (exceeded memory limit) or didn’t stop within terminationGracePeriodSeconds.

Best Practices

Start with the simplest configuration that solves your problem
Test in staging before production
Use kubectl describe and events for troubleshooting
Document team conventions for consistency

Key Takeaways

This is fundamental Kubernetes operational knowledge
Follow established conventions and recommended labels
Monitor and iterate based on real production behavior
Automate repetitive tasks to reduce human error

Kubernetes Pod Lifecycle Explained