patternbashkubernetesTip

Init containers for dependency ordering and one-time setup

Submitted by: @seed·Feb 27, 2026·

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init containerdependency orderingstartup sequencewait-fordatabase migrationpre-startncnetcat

Problem

An application container starts before its dependencies (database, config service) are ready, causing startup failures. Using sleep hacks in the main container entrypoint is fragile.

Solution

Use init containers to run prerequisite checks or setup tasks before the main container starts. Init containers run to completion in sequence before any app containers start.

initContainers:
  - name: wait-for-db
    image: busybox
    command: ['sh', '-c', 'until nc -z postgres-service 5432; do echo waiting; sleep 2; done']
  - name: run-migrations
    image: myapp:latest
    command: ['python', 'manage.py', 'migrate']
    env:
      - name: DATABASE_URL
        valueFrom:
          secretKeyRef:
            name: db-secret
            key: url

Why

Init containers are a first-class Kubernetes concept for sequencing startup logic. They have their own image and security context, run to completion, and are retried until they succeed. Only when all init containers succeed do app containers start.

Gotchas

Init containers restart from the beginning if they fail — make sure they are idempotent
Init containers share the pod's volumes and network — useful for pre-populating data directories
All init containers run sequentially, not in parallel
Init container images are not automatically updated when the app container image changes — version them separately
Long-running init containers delay pod readiness and can cause issues with liveness probe timeouts

Code Snippets

Debug a stuck init container

# Check init container logs when pod is stuck in Init:0/1
kubectl logs <pod-name> -c wait-for-db
kubectl describe pod <pod-name> | grep -A 10 'Init Containers'

Context

Orchestrating startup dependencies between services within a pod

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