Host mobile backend with FastAPI: streamed responses

Deploy a mobile backend 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 mobile backend-specific behavior as your application code.

Representative Queries

• Host mobile backend with FastAPI: streamed responses
• Where can I host Mobile backend built with FastAPI?
• I need a tested end-to-end streaming transport, timeout behavior and client disconnect handling.

Resource Requirements

• Compute
• Postgres

Infrastructure Requirements

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

Framework

FastAPI

Workload

Mobile backend

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

Success Checks

• app responds on its public URL

  • Kind: http_get
  • Path: /
  • Expect: ample canary fastapi patterns

• 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 mobile backend 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, quantity: 1.0, monthlyAmount: 5.0
  • Managed PostgreSQL database: s-1vcpu-1gb, quantity: 1.0, monthlyAmount: 5.0
• 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.

Next Actions

• Browse the catalog index:

  • Action ID: browse-catalog
  • Method: GET
  • Relative Path: /v1/catalog

• Search published recipes by intent, stack and constraints:

  • Action ID: search-recipes
  • Method: POST
  • Relative Path: /v1/catalog/search
  • Parameters: {"body":{"limit":5,"query":"Host mobile backend with FastAPI: streamed responses"}}

• Prepare a side-effect-free deployment plan for an authorized project:

  • Action ID: plan:page:recipes:mobile-backend:fastapi:response-streaming
  • Method: POST
  • Relative Path: /v1/catalog/plan
  • Parameters: {"body":{"inputs":{},"projectId":"","recipeId":"page:recipes:mobile-backend:fastapi:response-streaming","recipeRevision":"r1"}}

• Read the existing agent authentication setup:

  • Action ID: auth-setup
  • Method: GET
  • Relative Path: /mcp/setup

• Browse Mobile backend:

  • Action ID: browse:workload:mobile-backend
  • Method: GET
  • Relative Path: /v1/catalog/nodes/workload%3Amobile-backend

• Browse FastAPI:

  • Action ID: browse:stack:framework-fastapi
  • Method: GET
  • Relative Path: /v1/catalog/nodes/stack%3Aframework-fastapi

• Browse Streaming response service:

  • Action ID: browse:pattern:streaming-response-service
  • Method: GET
  • Relative Path: /v1/catalog/nodes/pattern%3Astreaming-response-service

• Browse Deploy API:

  • Action ID: browse:intent:deploy-api
  • Method: GET
  • Relative Path: /v1/catalog/nodes/intent%3Adeploy-api