Writing a backup strategy

A “strategy” knows how to dump and restore one kind of data store (Postgres, MySQL, Redis, raw volumes, …). To add one, implement the Strategy interface in internal/backup/ and register it.

Interface

type Strategy interface {
    Name() string                                       // unique key, e.g. "postgres"
    Detect(svc compose.Service) Confidence              // 0..1: should we suggest this?
    Backup(ctx context.Context, run *Run) error         // produce an artifact
    Restore(ctx context.Context, run *Run, src io.Reader) error
}

Run carries the app slug, target writer, working dir, and labels. The strategy is responsible for streaming the dump into run.Out and reporting bytes written.

Reference: Postgres

internal/backup/postgres.go:

1. Detect: returns 0.95 if the service image starts with postgres: or bitnami/postgresql; 0 otherwise.
2. Backup: shells pg_dump --format=custom --compress=6 inside the container via docker exec, captures stdout into run.Out. Reads POSTGRES_USER/POSTGRES_DB from the service env.
3. Restore: pg_restore --clean --if-exists.

Use it as the canonical template.

Steps to add a new strategy

1. Create internal/backup/<name>.go implementing Strategy.
2. Register the strategy in the factory (search for where Postgres is registered; add yours next to it).
3. Add a unit test that exercises Detect against a few compose services.
4. Add an integration test that runs Backup and Restore against a real container fixture (use the same pattern as internal/backup/postgres_test.go).
5. Add a row to the strategies table in Compose labels and a guide page under docs/guides/backups/<name>.md.
6. Mention the new strategy in docs/architecture/backup.md.

Constraints

• Network: only reach the target via the project’s docker network. Do not expose ports.
• Credentials: read from compose env vars or *_FILE secrets; never log them.
• Output: stream into run.Out. Do not buffer entire dumps in memory.
• Idempotency: a failed backup must be safe to retry.
• Cancellation: honor ctx; long-running dumps must exit when cancelled.

Submit

Open a PR with the strategy, tests, and docs. Tag it feat(backup): <name> strategy.