## Host rest api with FastAPI: worker execution and job state

### Summary
Deploy a rest api built with FastAPI as a public web service plus a dedicated worker process on Ample. `ample plan --write` discovers both services and their shared database and writes ample.toml; `ample up` reconciles the topology: a managed PostgreSQL 16 database, a public web microVM and a private worker microVM (kind worker, no public URL), both reading DATABASE_URL.

### Representative Queries
- Host rest api with FastAPI: worker execution and job state
- Where can I host REST API built with FastAPI?
- I need a separately runnable worker, durable job records and idempotent retries; not a managed queue.

### Resource Requirements
- Primitive: Compute
- Primitive: 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
REST API  
### Release Status
Published  
### Support Status
Verified  
### Execution Status
Ready  
### Prerequisites
- A repository with the web app and the worker as separate service directories (the fixture uses apps/web and apps/worker), each building and starting 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; the worker starts with python3 worker.py and binds no port).
- Both services read DATABASE_URL at runtime and share one jobs table; the worker claims rows with SELECT ... FOR UPDATE SKIP LOCKED and marks them done once.
- An Ample account token with servers:write and databases:write (ample up creates the database).

### Workflow Steps
1. **Plan the topology**  
   Run the planner once. It discovers the web and worker services, infers kind = "worker" for the process without a port, declares the database each service needs, and writes ample.toml. Exit 2 means it left questions in the manifest; answer them with --answer or by editing the file.  
   Command: `ample plan --write .`

2. **Share one database**  
   Keep a single [databases.main] with engine = "postgres", drop any per-service database the planner added, and set DATABASE_URL = { database = "main" } under both [services.web.env] and [services.worker.env]. Python services also need an explicit start command in the manifest (the fixture sets start for both services).  
   Command: `ample plan --offline .`

3. **Apply**  
   Reconcile the whole manifest in dependency order: the database first, then both services. It is idempotent and never destructive; exit 0 means everything applied, 2 needs input, 1 a failed resource (independent siblings still proceed and re-running resumes).  
   Command: `ample up .`

4. **Verify**  
   Fetch the web service URL and its worker status route (/p/worker-queue/status in the example) and confirm the worker processed the enqueued job; on failure read the worker service's runtime logs.  
   Command: `ample logs  --kind runtime`

### Limits and Considerations
- Verified on the python-3.12 template at s-1vcpu-1gb for both services with the example fixture; other sizes, templates and FastAPI major versions are not verified.
- The worker is a single long-running process supervised in its own microVM; there is no scheduler, cron or horizontal worker scaling in this recipe.

### Cost Estimate
- **Currency:** USD  
- **Monthly Amount:** 15.0  
- **Basis:** Size prices from pricing.toml (loaded by the API) at build revision 1ac5595375130d45290090e82ed0f554ccd45405-dirty.

#### Components
- Web server: s-1vcpu-1gb, $5.0
- Worker server: s-1vcpu-1gb, $5.0
- Managed PostgreSQL database: s-1vcpu-1gb, $5.0

### Evidence Summary
FastAPI web service plus a separate Python worker process deployed on Ample with `ample plan --write` then `ample up`. The web service enqueued a job that the private worker service consumed from the shared managed PostgreSQL database.

### Next Actions
- Browse the catalog index: `/v1/catalog`
- Search published recipes by intent, stack and constraints: `POST /v1/catalog/search`

### Example
- **Title:** FastAPI web + worker fixture  
  **Description:** A FastAPI web app (apps/web) and a worker process (apps/worker) sharing one managed PostgreSQL database; the queue module is under tests/deploy-canaries/_pattern-modules.  
  **Source Reference:** tests/deploy-canaries/fastapi-worker