practical/

Practical Migration Scenarios

These scenarios demonstrate zero-downtime techniques for common MongoDB changes. Each folder contains:

1. A short README describing the business context and rollout checklist.
2. One or more migrations that implement an expand/contract sequence.
3. Utilities for batching, resume-ability, and guardrails (e.g., safety switches, chunk sizes).

Included Scenarios

• add_column_expand_contract: Adds preferred_locale to customers.profile, backfills batches of 1,000 documents, then removes the legacy users.locale field.
• rename_field: Renames account_status to lifecycle_status using dual writes and staged cleanup.
• split_collection: Moves cold orders data older than 18 months into orders_archive while keeping writers online.
• data_backfill: Demonstrates idempotent, checkpointed enrichment of a products collection sourced from an external API.

Each scenario is written as Go migrations so they can be imported directly into an app. When running the CLI with --with-examples, these migrations are registered alongside the simpler examples/examplemigrations.