## Host mobile backend with FastAPI: stored input and output artifacts

Deploy a mobile backend built with FastAPI on Ample using the generated downloads pattern. Compute runs the app in an isolated microVM behind a public HTTPS URL, a managed PostgreSQL 16 database is auto-provisioned and injected as DATABASE_URL, a private S3-compatible bucket holds objects with credentials delivered as encrypted environment variables. Verified on FastAPI: an export query rendered to a CSV artifact stored with metadata in a private bucket and returned only to an authorized caller (401 without token, export=ok rows=3). Not separately tested: your export formats, retention policy and entitlement model; treat the mobile backend-specific behavior as your application code.

### Representative Queries
- Host mobile backend with FastAPI: stored input and output artifacts
- Where can I host Mobile backend built with FastAPI?
- I need an input/output artifact contract, object metadata and access boundaries.

### Prerequisites
- A FastAPI project that builds and starts with the documented commands (pip install into .ample/python from requirements.txt, then uvicorn from run.py reading PORT on the python-3.12 template)
- A PostgreSQL driver reading DATABASE_URL at runtime (auto-provisioned when omitted, or supplied with --env)
- A bucket from `ample bucket create` with its credentials passed as encrypted S3_* environment variables
- An Ample account token with servers:write, databases:read, buckets:read

### Workflow Steps
1. **Build and start**  
pip install into .ample/python from requirements.txt, then uvicorn from run.py reading PORT on the python-3.12 template. The server must bind 0.0.0.0 on PORT.
2. **Implement the pattern on PostgreSQL**  
The fixture's module implements generated downloads: an export query rendered to a CSV artifact stored with metadata in a private bucket and returned only to an authorized caller (401 without token, export=ok rows=3). Copy the approach into your schema; keep migrations idempotent and run them with --release-command.
3. **Wire object storage**  
Create the bucket(s), then pass endpoint, region, bucket and keys as --env values. Use path-style addressing. Keep private data in an unpublished bucket.
4. **Deploy**  
Run the synchronous deploy once and read the result (exit 0 live, 1 failed, 2 blocked). Re-running with no change is a no-op.
   
   ```bash
   ample deploy . --name --public --start "python3 run.py" --env S3_ENDPOINT=... --env S3_REGION=... --env S3_BUCKET=... --env S3_ACCESS_KEY_ID=... --env S3_SECRET_ACCESS_KEY=...
   ```
5. **Verify**  
Fetch the live URL and the pattern self-test route(s) (/p/generated-downloads) from the example; then run your own checks. On failure read `ample logs --kind build` then `--kind runtime`.
   
   ```bash
   ample logs --kind build
   ```

### Cost Estimate
- Monthly Amount: 10.0 USD  
- Components:
  - App Server: s-1vcpu-1gb - 5.0 USD
  - Managed PostgreSQL Database: s-1vcpu-1gb - 5.0 USD
- Note: Always-on monthly price of the tested sizes; apps and databases auto-pause when idle. Buckets are allocation-priced per quota and not included.

### Limitations
- Verified on the python-3.12 template at s-1vcpu-1gb with the example fixture; other sizes, templates and FastAPI major versions are not verified.
- The mobile backend itself (your export formats, retention policy and entitlement model) is application code and was not separately tested; the pattern checks are what was verified.
- Region, compliance attestations and request-duration limits are unknown and not claimed.
- Apps auto-pause when idle and wake on the next request; always-on is an operator setting, not a plan feature.
- Managed PostgreSQL 16 only; extensions, connection limits and backup or restore procedures are not verified; apps and their databases are placed together.
- PutObject and GetObject with path-style addressing are verified; multipart upload, listing, presigned URLs and lifecycle rules are not.

### Examples
- **FastAPI pattern fixture**  
Multi-pattern FastAPI app whose generated downloads module was checked live; the module is under tests/deploy-canaries/_pattern-modules.  
  
- Source Ref: `tests/deploy-canaries/fastapi-patterns`

### Success Checks
- App responds on its public URL
- Generated-downloads self-test

### Evidence Summary
- FastAPI pattern fixture deployed on Ample; checks passed for generated-downloads and configuration-secrets. Pattern proof: an export query rendered to a CSV artifact stored with metadata in a private bucket and returned only to an authorized caller.

### Last Verified At
- 2026-09-21T01:14:18Z

### Formats
- HTML: [Link](/content/recipes/mobile-backend/fastapi/artifact-storage/index.html)
- Markdown: [Link](/content/recipes/mobile-backend/fastapi/artifact-storage.md)
- JSON: [Link](https://api.ample.computer/v1/catalog/recipes/page%3Arecipes%3Amobile-backend%3Afastapi%3Aartifact-storage)