## Host ai chat application with Express: worker execution and job state

Deploy an ai chat application built with Express 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. Verified on Express: a separately deployed worker service (kind worker, no public URL) sharing a declared managed PostgreSQL database with the web service, consuming a jobs table with row locks and marking jobs done once (worker=done attempts=1). Not separately tested: your job payloads, retry policy and scheduling; treat the ai chat application-specific behavior as your application code.

### Representative Queries
- Host ai chat application with Express: worker execution and job state
- Where can I host AI chat application built with Express?
- I need a separately runnable worker, durable job records and idempotent retries; not a managed queue.

### Resource Requirements
1. **Compute**
2. **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. (verified)
- **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. (verified)

### 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 (npm install, npm run build --if-present, npm run start on the node-22 template; the worker starts with node worker (its own package.json start script) 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.
   - 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].  
   - 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`

### Examples
- **Express web + worker fixture**: A Express 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 Ref: `tests/deploy-canaries/express-worker`

### Success Checks
- web service responds on its public URL
   - Check: `ample canary express patterns`
- worker consumed the enqueued job
   - Check: `worker=done attempts=1 result=processed-by-worker`

### Limitations
- Verified on the node-22 template at s-1vcpu-1gb for both services with the example fixture; other sizes, templates and Express major versions are not verified.
- The ai chat application itself (your job payloads, retry policy and scheduling) is application code and was not separately tested; the worker-queue check is what was 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
- Monthly Amount: **$15.00**
   - Components:
     - Web server (size: s-1vcpu-1gb): $5.00
     - Worker server (size: s-1vcpu-1gb): $5.00
     - Managed PostgreSQL database (size: s-1vcpu-1gb): $5.00
     - Note: Always-on monthly price of the tested sizes; apps auto-pause when idle.

### Last Verified At
- **2026-09-20T03:56:46Z**

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