# Host mobile backend with Echo: worker execution and job state

## Summary
Deploy a mobile backend built with Echo 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 Echo: 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 mobile backend-specific behavior as your application code.

## Resource Requirements
- **Compute**
- **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.

## Prerequisites
1. 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 (CGO_ENABLED=0 go build -o app ./... then ./app on the ubuntu-24.04 template (go.sum committed for a reproducible build); the worker starts with ./worker and binds no port)
2. 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
3. An Ample account token with servers:write and databases:write (ample up creates the database)

## Tested Configuration
- Template: ubuntu-24.04
- Runtime: go
- Size: s-1vcpu-1gb
- Build: CGO_ENABLED=0 go build -o app ./...
- Start: ./app

## 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
- **Echo web + worker fixture**: A Echo 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/echo-worker`

## Success Checks
- Web service responds on its public URL
   - Kind: http_get
   - Path: /
   - Expect: ample canary echo patterns

- Worker consumed the enqueued job
   - Kind: http_get
   - Path: /p/worker-queue/status
   - Expect: worker=done attempts=1 result=processed-by-worker

## Limitations
1. Verified on the ubuntu-24.04 template at s-1vcpu-1gb for both services with the example fixture; other sizes, templates and Echo major versions are not verified.
2. The mobile backend itself (your job payloads, retry policy and scheduling) is application code and was not separately tested; the worker-queue check is what was verified.
3. 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, and the check ran immediately after deploy so idle behavior of the worker VM is not verified.
4. The worker service is private: it has no public URL and is reached only through the shared database; both services are placed with their database.
5. Managed PostgreSQL 16 only; extensions, connection limits and backup or restore procedures are not verified; apps and their databases are placed together.
6. Region, compliance attestations and request-duration limits are unknown and not claimed.