Host ai workflow runner with FastAPI: streamed responses

Summary

Deploy an AI workflow runner built with FastAPI on Ample using the streaming response service pattern. Compute runs the app in an isolated microVM behind a public HTTPS URL, with a managed PostgreSQL 16 database auto-provisioned and injected as DATABASE_URL. Verified on FastAPI: a Server-Sent Events endpoint reads incrementally through the public HTTPS gateway.

Infrastructure requirements

• 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: 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

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. 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. 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).

   ample deploy . --name <app-name> --public --start "python3 run.py"
   

4. Verify. Fetch the live URL and the pattern self-test route(s) from the example; then run your own checks. On failure read ample logs <deployment_id> --kind build then --kind runtime.

   ample logs <deployment_id> --kind build
   

Tested examples

• FastAPI pattern fixture: Multi-pattern FastAPI app whose streaming response service module was checked live.

Success checks

• App responds on its public URL.
• Streaming-response-service self-test.

Limitations

• Verified on the python-3.12 template. Other sizes, templates and FastAPI major versions are not verified.
• The AI workflow runner behavior is application code and was not separately tested.

Cost estimate

Estimated 10.00 USD per month:

• App server x1 s-1vcpu-1gb: 5.00 USD
• Managed PostgreSQL database x1 s-1vcpu-1gb: 5.00 USD

Verification evidence

• canary_run on 2026-09-21T01:14:18Z at revision ...: FastAPI pattern fixture deployed on Ample; checks passed for streaming-response-service and configuration-secrets. The evidence of a sever sent events endpoint and chunk observations was recorded.

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

Execution binding

MCP tool ample_deploy, schema hash observed at revision.