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Bad migrations kill apps. You risk data loss and downtime. Follow a system to stay safe.
Write idempotent migrations. The result stays the same if you run it ten times. Use IF NOT EXISTS. This makes retries safe.
Test on a copy of production data. Dev data is too clean. Production clones show real edge cases.
Keep changes backward compatible. Never delete a column in one go. Add the new one first. Update your code to write to both. Delete the old one later. This stops downtime.
Use the expand-migrate-contract pattern for big changes.
- Expand the schema.
- Migrate data.
- Contract by removing old parts.
Avoid locking tables. Adding columns with defaults locks PostgreSQL. Add the column without a default. Update data in batches. Set the default last.
Run migrations outside app startup. Use a dedicated runner. This keeps your app available.
Plan for failure. Write a tested rollback script for every change. Document the time and lock duration.
Build for today. Do not build for scale you do not have. Start with a simple core path. Add observability early. Use boring tech your team knows.
Next steps:
- Audit your backend this week.
- Implement one new pattern this month.
- Review your ops this quarter.
Source: https://dev.to/therizwansaleem/database-migration-strategies-zero-downtime-rollback-and-testing-3pdj