page:recipes:mobile backend:fastapi:persistent state

Host mobile backend with FastAPI: Postgres-backed state

Deploy a mobile backend built with FastAPI on Ample using the durable job state 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 jobs table with a state and attempts counter, processing inside a row-locked transaction, and a second run that is a no-op (job=done attempts=1 idempotent=true). Not separately tested: your job types, payload schema and retry policy; treat the mobile backend-specific behavior as your application code.

Representative Queries

• Host mobile backend with FastAPI: Postgres-backed state
• Where can I host Mobile backend built with FastAPI?
• I need a durable state schema and retry/recovery semantics implemented by application code.

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

Input Schema

• env: Encrypted environment variables (bucket credentials, secrets)
  • type: array
  • items:
    • type: string pattern: "^[A-Z][A-Z0-9_]=.$"
  • maxItems: 50
• name: App name
  • type: string
  • maxLength: 63
  • minLength: 1
  • pattern: "^[a-z0-9-]+$"
• path: Project directory or ample.toml service
  • type: string
  • maxLength: 512
  • minLength: 1
• release_command: Migration command run before activation
  • type: string
  • maxLength: 512
• start: Start command (Python apps pass one explicitly)
  • type: string
  • maxLength: 512

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 durable job state: a jobs table with a state and attempts counter, processing inside a row-locked transaction, and a second run that is a no-op (job=done attempts=1 idempotent=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/durable-job-state) 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 durable job state 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. Durable-job-state self-test
   • Kind: http_get
   • Path: /p/durable-job-state
   • Expect: job=done attempts=1 idempotent=true

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 job types, payload schema and retry policy) 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:
    • Size: s-1vcpu-1gb
    • Quantity: 1.0
    • Monthly Amount: 5.0
  • Managed PostgreSQL Database:
    • Size: s-1vcpu-1gb
    • Quantity: 1.0
    • Monthly Amount: 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.

Evidence Summary

1. Canary Run: FastAPI pattern fixture deployed on Ample; checks passed for durable-job-state and configuration-secrets.
   • Observed At: 2026-09-21T01:14:18Z
   • Summary: FastAPI pattern fixture deployed; checks passed.

Formats

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• JSON: Link

Next Actions

1. Browse the catalog index
2. Search published recipes by intent, stack and constraints
3. Prepare a side-effect-free deployment plan for an authorized project
4. Read the existing agent authentication setup
5. Browse Mobile backend
6. Browse FastAPI
7. Browse Durable job state
8. Browse Deploy API