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

### 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**