### Host rest api with FastAPI: streamed responses

Deploy a rest api built with FastAPI on Ample using the streaming response service 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. Verified on FastAPI: a Server-Sent Events endpoint read incrementally through the public HTTPS gateway: five one-second chunks arrived spread over time with the first within seconds (not buffered), a 70-second stream of 36 chunks completed past common 60-second idle timeouts, and a client that disconnected after two chunks was observed and recorded by the server (disconnected=true). Not separately tested: your event schema, reconnection strategy and any per-request duration ceiling beyond the 70 seconds measured; treat the rest api-specific behavior as your application code.

#### Representative Queries
- Host rest api with FastAPI: streamed responses
- Where can I host REST API built with FastAPI?
- I need a tested end-to-end streaming transport, timeout behavior and client disconnect handling.

#### Resource Requirements
- `primitive:compute`
- `primitive:postgres`

#### Infrastructure Requirements
1. **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.
2. **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
- 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)
- An Ample account token with servers:write, databases:read

#### 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

#### 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 streaming response service: a Server-Sent Events endpoint read incrementally through the public HTTPS gateway: five one-second chunks arrived spread over time with the first within seconds (not buffered), a 70-second stream of 36 chunks completed past common 60-second idle timeouts, and a client that disconnected after two chunks was observed and recorded by the server (disconnected=true). Copy the approach into your schema; keep migrations idempotent and run them with --release-command.
3. **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.  
   Command: ample deploy . --name --public --start "python3 run.py"
4. **Verify**  
   Fetch the live URL and the pattern self-test route(s) (/p/streaming-response-service) from the example; then run your own checks. On failure read `ample logs --kind build` then `--kind runtime`.  
   Command: ample logs --kind build

#### Examples
- **FastAPI pattern fixture**  
   Multi-pattern FastAPI app whose streaming response service module was checked live; the module is under tests/deploy-canaries/_pattern-modules.

#### Success Checks
1. **app responds on its public URL**  
   - Kind: http_get  
   - Path: /  
   - Expect: ample canary fastapi patterns
2. **streaming-response-service self-test**  
   - Kind: http_get  
   - Path: /p/streaming-response-service  
   - Expect: an SSE stream: data: id=, then chunk events one interval apart (read incrementally: first chunk within seconds, chunks spread over the interval), then data: done; /status?id= reports sent=N disconnected=true|false done=true|false

#### 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 rest api itself (your event schema, reconnection strategy and any per-request duration ceiling beyond the 70 seconds measured) 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.

#### Cost Estimate
- **Currency**: USD  
- **Monthly Amount**: 10.0  
- **Basis**: size prices from pricing.toml (loaded by the API) at build revision 1ac5595375130d45290090e82ed0f554ccd45405-dirty  
- **Components**:  
  - app server: s-1vcpu-1gb (1.0 unit) - $5.00
  - managed PostgreSQL database: s-1vcpu-1gb (1.0 unit) - $5.00  
- **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.

#### Evidence Summary
- **Canary run**  
   - Summary: 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); checks passed for streaming-response-service and configuration-secrets. Pattern proof: a Server-Sent Events endpoint read incrementally through the public HTTPS gateway: five one-second chunks arrived spread over time with the first within seconds (not buffered), a 70-second stream of 36 chunks completed past common 60-second idle timeouts, and a client that disconnected after two chunks was observed and recorded by the server (disconnected=true).
   - 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/streaming-response-service]  
     - Pattern: pattern:streaming-response-service  
     - Template: python-3.12
- **Last Verified At**: 2026-09-21T01:14:18Z

#### Next Actions
- **Browse the catalog index**  
   - Operation ID: catalog_index  
   - Method: GET  
   - Relative Path: /v1/catalog
- **Search published recipes by intent, stack and constraints**  
   - Operation ID: search_recipes  
   - Method: POST  
   - Relative Path: /v1/catalog/search  
   - Parameters: {"body":{"limit":5,"query":"Host rest api with FastAPI: streamed responses"}}  
- **Prepare a side-effect-free deployment plan for an authorized project**  
   - Operation ID: plan_deployment  
   - Method: POST  
   - Relative Path: /v1/catalog/plan  
   - Parameters: {"body":{"inputs":{},"projectId":"","recipeId":"page:recipes:rest-api:fastapi:response-streaming","recipeRevision":"r1"}}  
- **Read the existing agent authentication setup**  
   - Operation ID: existing_auth_setup  
   - Method: GET  
   - Relative Path: /mcp/setup
- **Browse REST API**  
   - Operation ID: browse_node  
   - Method: GET  
   - Relative Path: /v1/catalog/nodes/workload%3Arest-api  
   - Parameters: {"nodeId":"workload:rest-api"}  
- **Browse FastAPI**  
   - Operation ID: browse_node  
   - Method: GET  
   - Relative Path: /v1/catalog/nodes/stack%3Aframework-fastapi  
   - Parameters: {"nodeId":"stack:framework-fastapi"}  
- **Browse Streaming response service**  
   - Operation ID: browse_node  
   - Method: GET  
   - Relative Path: /v1/catalog/nodes/pattern%3Astreaming-response-service  
   - Parameters: {"nodeId":"pattern:streaming-response-service"}  
- **Browse Deploy API**  
   - Operation ID: browse_node  
   - Method: GET  
   - Relative Path: /v1/catalog/nodes/intent%3Adeploy-api  
   - Parameters: {"nodeId":"intent:deploy-api"}