page:recipes:rest api:express:worker state

Host rest api with Express: worker execution and job state

Summary

Deploy a rest api 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).

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)

Resource Requirements

• Compute
• 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.

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].
   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.

Success Checks

• web service responds on its public URL: ample canary express patterns
• worker consumed the enqueued job: 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 rest api 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

• Currency: USD
• Monthly Amount: 15.0
• Components:
  • web server, size s-1vcpu-1gb, quantity 1.0, monthly amount 5.0
  • worker 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 auto-pause when idle.