Migrate Heroku app: FastAPI

Move FastAPI compute from Heroku app to Ample, one component at a time. Destination verified on Ample: the app built, started and answered on its public HTTPS URL with encrypted configuration delivered.

Summary

Source procedure: Export config vars with heroku config -s -a into an env file kept out of the repository. Not migrated automatically: Heroku add-ons other than Postgres, release-phase scheduling, dyno autoscaling and Heroku Scheduler are not migrated; use --release-command for release tasks.

Cutover: Add the custom domain with ample domain add, update DNS from the Heroku DNS target, keep the Heroku app until verified, then scale it down.

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

Representative Queries

• Migrate Heroku app: FastAPI
• Where can I host FastAPI built with FastAPI?
• I need a component-scoped export/import or reconfiguration procedure for FastAPI, with compatibility checks, verification and rollback.

Resource Requirements

• Compute
• Postgres

Infrastructure Requirements

• Compute
  • Status: verified
  • Summary: Apps run in isolated x86_64 Firecracker microVMs that auto-pause when idle and wake on request; sizes are the priced VM sizes.
• Postgres
  • Status: verified
  • Summary: Managed PostgreSQL 16 runs in its own microVM and is auto-provisioned when an app needs a database and no DATABASE_URL is supplied.

Prerequisites

• Authorized access to the Heroku app 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

Migration Steps

1. Inventory the source
   List what Heroku app provides beyond the component you are moving. Out of scope here: Heroku add-ons other than Postgres, release-phase scheduling, dyno autoscaling and Heroku Scheduler are not migrated; use --release-command for release tasks.
2. Source step 1
   Export config vars with heroku config -s -a into an env file kept out of the repository.
3. Source step 2
   Translate the Procfile web process into the start command (--start or the package manifest's start script); worker processes need a separate --kind worker service.
4. Source step 3
   Note buildpacks and add-ons in use; managed databases replace Heroku Postgres, while other add-ons need their own plan.
5. Deploy on Ample in parallel
   pip install into .ample/python from requirements.txt, then uvicorn from run.py reading PORT on the python-3.12 template. Pass the exported variables with --env; keep the source running.

   ample deploy . --name <name> --public --start "python3 run.py" --env-file .env.production
   

6. Validate before cutover
   Run the app's own checks and, for data, compare counts and checksums; example checks include self-tests (/p/configuration-secrets, /p/relational-records).
7. Cut over
   Add the custom domain with ample domain add, update DNS from the Heroku DNS target, keep the Heroku app until verified, then scale it down.
8. Rollback
   Point DNS or configuration back to the source. The source was never modified; deletion is a separate, user-executed step after validation.

Success Checks

• Destination app responds on its public URL
  • Kind: http_get
  • Path: /
  • Expect: ample canary fastapi patterns
• Configuration-secrets check
  • Kind: http_get
  • Path: /p/configuration-secrets
  • Expect: see the pattern fixture checks
• Relational-records check
  • Kind: http_get
  • Path: /p/relational-records
  • Expect: see the pattern fixture checks
• Data or object counts and checksums match the source
  • Kind: manual
  • Expect: 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 app'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 add-ons other than Postgres, release-phase scheduling, dyno autoscaling and Heroku Scheduler are not migrated; use --release-command for release tasks.
• Verified on the python-3.12 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.

Cost Estimate

• Currency: USD
• Monthly Amount: $10.00
• Note: Destination always-on monthly price of the tested sizes; apps auto-pause when idle. Source costs are unknown to Ample.
• Components:
  • App server
    • Size: s-1vcpu-1gb
    • Monthly Amount: $5.00
  • Managed PostgreSQL database
    • Size: s-1vcpu-1gb
    • Monthly Amount: $5.00

Evidence Summary

• Kind: canary_run
  • Summary: Destination side verified: the FastAPI pattern fixture deployed on Ample and its checks passed. The source-side export from Heroku app is documented and was not executed by this catalog's evidence.
  • Observed At: 2026-09-21T01:14:18Z
  • Implementation Revision: 50dbac567d2c5cc8e55e6c748a646be0025d9cfb-dirty (CLI 0.1.21)
  • Expires At: 2027-03-20T01:14:18Z
  • Scope:
    • Checks: /p/configuration-secrets, /p/relational-records
    • Destination Only: true
    • Template: python-3.12

Last Verified At

• 2026-09-21T01:14:18Z.