Hooks & Lifecycle

🔥 Vibe Prompt

"Add Helm hooks: pre-install DB migration, post-install notification, pre-upgrade backup."

Hook Types

apiVersion: batch/v1
kind: Job
metadata:
  name: db-migrate
  annotations:
    "helm.sh/hook": pre-install,pre-upgrade
    "helm.sh/hook-weight": "-5"
    "helm.sh/hook-delete-policy": hook-succeeded
spec:
  template:
    spec:
      restartPolicy: Never
      containers:
        - name: migration
          image: myapp:latest
          command: ["npm", "run", "migrate"]
---
apiVersion: v1
kind: Pod
metadata:
  name: notify
  annotations:
    "helm.sh/hook": post-install,post-upgrade
    "helm.sh/hook-weight": "10"
spec:
  restartPolicy: Never
  containers:
    - image: curlimages/curl
      command: ["curl", "-X", "POST", "https://hooks.slack.com/..."]

Hook Order (by weight)

-10  pre-install (backup)
 -5  pre-install (migration)
  0  install (main chart)
  5  post-install (verify)
 10  post-install (notify)

Lifecycle Best Practices

| Hook | Use Case | |------|----------| | pre-install | DB creation, schema setup | | post-install | Notification, cache warmup | | pre-upgrade | Backup, migration | | post-upgrade | Smoke test, rollback check | | pre-delete | Snapshot, cleanup | | post-delete | Notification |

Rollback Safety

annotations:
  "helm.sh/hook": pre-upgrade
  "helm.sh/hook-delete-policy": before-hook-creation

Complete Lifecycle

helm install → pre-install hooks → install → post-install hooks
helm upgrade → pre-upgrade hooks → upgrade → post-upgrade hooks
helm rollback → (re-runs upgrade hooks)
helm delete → pre-delete hooks → delete → post-delete hooks

Chapter Summary

Understand core concepts and principles
Master implementation methods and techniques
Familiar with common issues and solutions
Able to apply in real projects

Implementation Example

Basic Example

# This section provides a complete implementation example

Steps

Setup: Configure development environment
Data: Prepare required data
Implementation: Build core functionality
Testing: Verify correctness
Optimization: Improve performance

Common Errors

| Error Type | Cause | Solution | |------------|-------|----------| | Compilation | Syntax | Check code syntax | | Runtime | Environment | Verify dependencies installed | | Logic | Algorithm | Step-by-step debugging | | Performance | Efficiency | Use profilers |

Code Example

import sys

def main():
    print("Hello, World!")

if __name__ == "__main__":
    main()

References

Official documentation
API reference
Open source examples
Community discussions

Hook Weights and Execution Order

Hooks can run in a specific order using weights. Without weights, hooks run concurrently.

Weight System

| Weight Range | Execution Order | |-------------|----------------| | -100 to -1 | Before default (pre-hooks run first) | | 0 (default) | Default priority | | 1 to 100 | After default |

annotations:
  "helm.sh/hook": pre-install
  "helm.sh/hook-weight": "-5"

Hook Chain Example

pre-install (-10) → pre-install (-5) → pre-install (0) → install → post-install (0) → post-install (5)

Hook Deletion Policies

Control whether hook resources are deleted after execution.

| Policy | Behavior | |--------|----------| | before-hook-creation | Delete before new hook runs | | hook-succeeded | Delete only on success | | hook-failed | Delete only on failure |

annotations:
  "helm.sh/hook": post-install
  "helm.sh/hook-delete-policy": hook-succeeded

Practical Use Cases

Database Migration

apiVersion: batch/v1
kind: Job
metadata:
  name: {{ include "myapp.fullname" . }}-migrate
  annotations:
    "helm.sh/hook": post-install,post-upgrade
    "helm.sh/hook-weight": "-5"
    "helm.sh/hook-delete-policy": hook-succeeded
spec:
  template:
    spec:
      restartPolicy: Never
      containers:
      - name: migrate
        image: "{{ .Values.image.repository }}:{{ .Values.image.tag }}"
        command: ["node", "scripts/migrate.js"]
        env:
        - name: DATABASE_URL
          valueFrom:
            secretKeyRef:
              name: {{ .Values.database.existingSecret }}
              key: url

Pre-Install Validation

apiVersion: batch/v1
kind: Job
metadata:
  name: {{ include "myapp.fullname" . }}-validate
  annotations:
    "helm.sh/hook": pre-install,pre-upgrade
    "helm.sh/hook-weight": "-10"
    "helm.sh/hook-delete-policy": before-hook-creation,hook-succeeded
spec:
  template:
    spec:
      restartPolicy: Never
      containers:
      - name: validate
        image: bitnami/kubectl:latest
        command:
        - sh
        - -c
        - |
          kubectl get namespace {{ .Values.global.namespace }} || exit 1
          kubectl get secret {{ .Values.database.existingSecret }} || exit 1

Cleanup Job

apiVersion: batch/v1
kind: Job
metadata:
  name: {{ include "myapp.fullname" . }}-cleanup
  annotations:
    "helm.sh/hook": pre-delete
    "helm.sh/hook-weight": "0"
    "helm.sh/hook-delete-policy": hook-succeeded
spec:
  template:
    spec:
      restartPolicy: Never
      containers:
      - name: cleanup
        image: bitnami/kubectl:latest
        command:
        - sh
        - -c
        - |
          kubectl delete pvc -l app.kubernetes.io/instance={{ .Release.Name }}

Testing Hooks Locally

# Dry run to see hook order
helm install myapp ./myapp --dry-run

# Install with hooks
helm install myapp ./myapp

# Check hook jobs
kubectl get jobs -n default
kubectl logs job/myapp-migrate

# Upgrade triggers hooks again
helm upgrade myapp ./myapp

Common Mistakes

| Mistake | Consequence | Fix | |---------|-------------|-----| | No delete policy | Old jobs accumulate | Add hook-delete-policy | | Wrong hook type | Runs at wrong time | Verify hook annotation | | Missing weight | Concurrent execution | Add weight for ordering | | No error handling | Failed hooks ignored | Add activeDeadlineSeconds | | Heavy dependencies | Slow installation | Keep hooks lightweight |

Summary

Helm hooks enable lifecycle automation — running jobs before, after, or during releases. Use weights for ordering and delete policies to clean up.

Key takeaways:

Helm hooks: pre/post install, upgrade, rollback, delete, test |
Hooks are Kubernetes resources (Jobs, Pods) with special annotations |
Hook weights control execution order (-100 to 100) |
Delete policies prevent resource accumulation |
Common hooks: DB migration, validation, backup, cleanup |
Test hooks verify release functionality |
Always handle hook failures gracefully |

What's Next: Security Best Practices

The next chapter covers Helm security best practices.