Run a Migration in an Init Container
Put the database migration in an init container so the app container starts only after the schema is at the expected version.
Task
Configure initContainers: [{ name: 'migrate', image: 'api:migrate', command: ['pnpm', 'migrate'] }] so the cluster enforces the policy at admission time instead of relying on manual review.
When to use this
A developer deploys a pod without initContainers: [{ name: 'migrate', image: 'api:migrate', command: ['pnpm', 'migrate'] }] and it disrupts a node, causing evictions on a production cluster.
Prerequisites
- A Kubernetes cluster with kubectl access
- Cluster admin or namespace edit RBAC
Steps
1. Configure initContainers: [{ name: 'migrate', image: 'api:migrate', command: ['pnpm', 'migrate'] }] in the project configuration file with the recommended defaults.
initContainers: [{ name: 'migrate', image: 'api:migrate', command: ['pnpm', 'migrate'] }]
Expected output: The configuration is accepted and initContainers: [{ name: 'migrate', image: 'api:migrate', command: ['pnpm', 'migrate'] }] runs without errors on the first invocation.
2. Run the check locally to verify initContainers: [{ name: 'migrate', image: 'api:migrate', command: ['pnpm', 'migrate'] }] produces the expected result before pushing.
act -j build # or: pnpm test
Expected output: Local run matches CI behavior; no surprises after push.
3. Add the gate to the CI pipeline so initContainers: [{ name: 'migrate', image: 'api:migrate', command: ['pnpm', 'migrate'] }] blocks merge on failure.
- name: Run add init container migration
run: pnpm test
Expected output: Pull requests with failing initContainers: [{ name: 'migrate', image: 'api:migrate', command: ['pnpm', 'migrate'] }] are blocked from merging.
Troubleshooting
Problem
The check passes locally but fails in CI
Solution
Pin dependency versions and the runtime to match CI exactly; reproduce with the same Docker image or act.
Problem
Configuration is rejected with a schema error
Solution
Check the tool version matches the config schema; older versions may not support newer fields.
Limitations
- The gate only runs on events that trigger the workflow; locally pushed commits bypass it.
- Configuration drift is possible if someone edits settings outside version control.
Enforce at admission
Start by measuring the problem. Put the database migration in an init container so the app container starts only after the schema is at the expected version. The most common mistake is adding the gate without first confirming it catches the issue you care about. Run initContainers: [{ name: ‘migrate’, image: ‘api:migrate’, command: [‘pnpm’, ‘migrate’] }] against the current codebase and inspect the output before wiring it into CI.
initContainers: [{ name: 'migrate', image: 'api:migrate', command: ['pnpm', 'migrate'] }]Verify the policy
Once the gate is in place, make failures actionable. A failing initContainers: [{ name: ‘migrate’, image: ‘api:migrate’, command: [‘pnpm’, ‘migrate’] }] should point to the exact file and line, not a generic error. Pin the tool version in the lockfile so a upstream release does not silently change behavior. Review the gate output in every pull request just like a test result.