ETL Core Patterns Reliability patterns for production data pipelines. Idempotency Patterns Checkpointing Error Handling Chunked Processing Retry Logic Logging Best Practices Data Migration Scripts Create production-safe migration scripts with rollback and validation. Migration Template (PostgreSQL) Rollback Script Python Migration Framework Safe Migration Patterns Migration Safety Checklist Before: tested on staging, rollback tested, backup taken, maintenance window scheduled. After: validation queries passed, application health checked, performance normal. ---