# Migrate Heroku Postgres: Transactional workflows

Move PostgreSQL data from Heroku Postgres to Ample, one component at a time. Destination verified on Ample: an optimistic version check and an event row written in the same transaction, a stale update rejected, and a history query over the application-owned events (history=2 conflict=rejected).

**Source procedure:** Take a logical backup with `heroku pg:backups:capture` and download it, or `pg_dump -Fc` against the credentials from `heroku pg:credentials:url`. Not migrated automatically: Heroku Postgres followers, forks, rollback (PITR) and dataclips have no equivalent on the managed database.

**Cutover:** Put the app in maintenance mode with the user's go-ahead, take the final backup, restore, validate, redeploy with the managed DATABASE_URL, keep the Heroku database until confirmed.

**Rollback:** Keep the source untouched until you confirm; nothing at the source is changed or deleted by this guide.

## Prerequisites
- Authorized access to the Heroku Postgres source and its export tooling
- An inventory of every component in scope and out of scope
- A validated backup or copy before any cutover
- An Ample account token with servers:write, databases:read

## Workflow Steps
1. **Inventory the source**  
   List what Heroku Postgres provides beyond the component you are moving. Out of scope here: Heroku Postgres followers, forks, rollback (PITR) and dataclips have no equivalent on the managed database.

2. **Source step 1**  
   Take a logical backup with `heroku pg:backups:capture` and download it, or `pg_dump -Fc` against the credentials from `heroku pg:credentials:url`.

3. **Source step 2**  
   Check the Postgres major version and extensions against the managed engine (PostgreSQL 16).

4. **Source step 3**  
   Restore into a scratch managed database first and compare row counts.

5. **Provision and restore**  
   Deploy the app once so a managed PostgreSQL 16 database exists (or create one with `ample database create --engine postgres`), then restore the dump with pg_restore using its connection string; keep migrations idempotent.

6. **Validate before cutover**  
   Run the app's own checks and, for data, compare counts and checksums; the example checks are the pattern self-tests (/p/transactional-workflows).

7. **Cut over**  
   Put the app in maintenance mode with the user's go-ahead, take the final backup, restore, validate, redeploy with the managed DATABASE_URL, keep the Heroku database until confirmed.

8. **Rollback**  
   Point DNS or configuration back to the source. The source was never modified; deletion is a separate, user-executed step after validation.

## Examples
- **Express pattern fixture (destination)**  
  Verified destination basis: transactional workflows.  
  Source reference: `tests/deploy-canaries/express-patterns`.

## Success Checks
- Destination app responds on its public URL: **Expected**  `ample canary express patterns`.
- Transactional workflows check from the destination example: **Expected** `see the pattern fixture checks`.
- Data or object counts and checksums match the source: **Expected** `operator comparison before cutover`.

## Limitations
- Documentation only: nothing is executed automatically and no execution binding is offered.
- The source-side procedure is documented from Heroku Postgres's standard tooling and was not executed in this catalog's evidence; the destination side was verified with the pattern fixture.
- No full source-product parity is claimed: Heroku Postgres followers, forks, rollback (PITR) and dataclips have no equivalent on the managed database.
- Verified on the node-22 template at s-1vcpu-1gb; region, compliance and request-duration limits are unknown.
- Managed PostgreSQL 16 only; extensions, connection limits and backup or restore procedures on the managed side are not verified beyond the pattern checks.