Run a Zero-Downtime Migration in Three Phases

Split the migration into expand, migrate, and contract phases so the old and new code run side by side during the transition.

~30 mindatabasemigrationzero-downtime

Task

Apply pnpm migrate:up --expand && deploy && pnpm migrate:up --contract so the schema change is safe, reversible, and does not lock the table during peak traffic.

When to use this

A migration deploys pnpm migrate:up --expand && deploy && pnpm migrate:up --contract during peak hours, takes a 40-second lock, and causes a connection pool exhaustion.

Prerequisites

A database with migration tooling configured
A staging environment mirroring production schema

Steps

1. Configure pnpm migrate:up --expand && deploy && pnpm migrate:up --contract in the project configuration file with the recommended defaults.

pnpm migrate:up --expand && deploy && pnpm migrate:up --contract

Expected output: The configuration is accepted and pnpm migrate:up --expand && deploy && pnpm migrate:up --contract runs without errors on the first invocation.

2. Run the check locally to verify pnpm migrate:up --expand && deploy && pnpm migrate:up --contract produces the expected result before pushing.

pnpm test

Expected output: Local run matches CI behavior; no surprises after push.

3. Add the gate to the CI pipeline so pnpm migrate:up --expand && deploy && pnpm migrate:up --contract blocks merge on failure.

- name: Run add migration zero downtime
  run: pnpm test

Expected output: Pull requests with failing pnpm migrate:up --expand && deploy && pnpm migrate:up --contract 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.

Make migrations safe

Start by measuring the problem. Split the migration into expand, migrate, and contract phases so the old and new code run side by side during the transition. The most common mistake is adding the gate without first confirming it catches the issue you care about. Run pnpm migrate:up –expand && deploy && pnpm migrate:up –contract against the current codebase and inspect the output before wiring it into CI.

pnpm migrate:up --expand && deploy && pnpm migrate:up --contract

Verify and roll back

Once the gate is in place, make failures actionable. A failing pnpm migrate:up –expand && deploy && pnpm migrate:up –contract 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.