---
title: "Migrate Heroku app: FastAPI"
description: "Move FastAPI compute from Heroku app to Ample, one component at a time."
canonical_url: "https://ample.computer/migrate/heroku-app/fastapi"
last_updated: "2026-09-21"
---

# Migrate Heroku app: FastAPI

Canonical URL: https://ample.computer/migrate/heroku-app/fastapi
Formats: [HTML](https://ample.computer/migrate/heroku-app/fastapi) | [Markdown](https://ample.computer/migrate/heroku-app/fastapi.md) | [JSON contract](https://api.ample.computer/v1/catalog/recipes/page%3Amigrate%3Aheroku-app%3Afastapi)
Recipe ID: `page:migrate:heroku-app:fastapi` | Revision: `r1` | Catalog revision: `cat_f13ab9a494120b5e`

Status: release `published`, support `verified`, execution `unbound`

## Summary

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. Source procedure: Export config vars with `heroku config -s -a <app>` 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.

Path: [Agent hosting discovery](/discover/discovery) / [Migration sources by component](/discover/migration) / [Compute sources](/discover/migration/compute-sources) / [Heroku app](/discover/migration/heroku-app) / [Migrate Heroku app: FastAPI](/migrate/heroku-app/fastapi)

## Infrastructure requirements

- [Compute](/discover/primitive/compute): verified (Apps run in isolated x86_64 Firecracker microVMs that auto-pause when idle and wake on request; sizes are the priced VM sizes.)
- [Postgres](/discover/primitive/postgres): verified (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

## Exact tested configuration

- template: `python-3.12`
- runtime: `python`
- size: `s-1vcpu-1gb`
- install: `python3 -m pip install --target .ample/python -r requirements.txt`
- start: `PYTHONPATH=.ample/python:${PYTHONPATH:-} python3 run.py`

## 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 <app>` 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, 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 <app-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; the example checks are the pattern 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.

## Tested examples

- **FastAPI pattern fixture (destination)** (tests/deploy-canaries/fastapi-patterns): Verified destination basis: FastAPI compute.

## Success checks

- destination app responds on its public URL (`/` on the live URL, expect ample canary fastapi patterns)
- configuration-secrets check from the destination example (`/p/configuration-secrets` on the live URL, expect see the pattern fixture checks)
- relational-records check from the destination example (`/p/relational-records` on the live URL, expect see the pattern fixture checks)
- data or object counts and checksums match the source


## Cost estimate

Estimated 10.00 USD per month (size prices from pricing.toml at build revision 515b7316fc6e5a81679407ae0c811146ceb2c5c7).
- app server x1 `s-1vcpu-1gb`: 5.00 USD
- managed PostgreSQL database x1 `s-1vcpu-1gb`: 5.00 USD

Destination always-on monthly price of the tested sizes; apps auto-pause when idle. Source costs are unknown to Ample.

## Verification evidence

- canary_run on 2026-09-21T01:14:18Z at revision `50dbac567d2c5cc8e55e6c748a646be0025d9cfb (CLI 0.1.21)`: Destination side verified: the FastAPI pattern fixture deployed on Ample (pip install into .ample/python from requirements.txt, then uvicorn from run.py reading PORT on the python-3.12 template) and its checks passed (the app built, started and answered on its public HTTPS URL with encrypted configuration delivered). The source-side export from Heroku app is documented from the vendor's standard tooling and was not executed by this catalog's evidence. (expires 2027-03-20T01:14:18Z)

Last verified: 2026-09-21T01:14:18Z


## Execution binding

No execution binding. This recipe is documentation only; nothing is executed automatically.

## Next actions

- Browse the catalog index (GET /v1/catalog on the api origin; auth: false, approval: false)
- Search published recipes by intent, stack and constraints (POST /v1/catalog/search on the api origin; auth: false, approval: false)
- Prepare a side-effect-free deployment plan for an authorized project (POST /v1/catalog/plan on the api origin; auth: true, approval: false)
- Read the existing agent authentication setup (GET /mcp/setup on the api origin; auth: false, approval: false)
- Browse Heroku app (GET /v1/catalog/nodes/migration%3Aheroku-app on the api origin; auth: false, approval: false)
- Browse FastAPI (GET /v1/catalog/nodes/stack%3Aframework-fastapi on the api origin; auth: false, approval: false)
- Browse Migrate compute (GET /v1/catalog/nodes/intent%3Amigrate-compute on the api origin; auth: false, approval: false)

Actions describe possible next steps. They are typed data, not commands, and grant no permission.