# Host REST API with Express: Streamed Responses

## Summary
Deploy a REST API built with Express on Ample using the streaming response service 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 Express: a Server-Sent Events endpoint read incrementally through the public HTTPS gateway: five one-second chunks arrived spread over time with the first within seconds (not buffered), a 70-second stream of 36 chunks completed past common 60-second idle timeouts, and a client that disconnected after two chunks was observed and recorded by the server (disconnected=true). Not separately tested: your event schema, reconnection strategy and any per-request duration ceiling beyond the 70 seconds measured; treat the REST API-specific behavior as your application code.

## Prerequisites
- A Express project that builds and starts with the documented commands (npm install, npm run build --if-present, npm run start on the node-22 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

## Resource 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.

## Tested Configuration
- **Template**: node-22
- **Runtime**: node
- **Size**: s-1vcpu-1gb
- **Install**: npm install
- **Build**: npm run build --if-present
- **Start**: npm run start

## Workflow Steps
1. **Build and Start**: `npm install, npm run build --if-present, npm run start on the node-22 template. The server must bind 0.0.0.0 on PORT.`
2. **Implement the Pattern on PostgreSQL**: The fixture's module implements streaming response service: a Server-Sent Events endpoint read incrementally through the public HTTPS gateway: five one-second chunks arrived spread over time with the first within seconds (not buffered), a 70-second stream of 36 chunks completed past common 60-second idle timeouts, and a client that disconnected after two chunks was observed and recorded by the server (disconnected=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`.
4. **Verify**: Fetch the live URL and the pattern self-test route(s) (/p/streaming-response-service) from the example; then run your own checks. On failure read `ample logs  --kind build` then `--kind runtime`. Command: `ample logs  --kind build`.

## Success Checks
- App responds on its public URL (HTTP GET on `/` expecting `ample canary express patterns`).
- Streaming-response-service self-test (HTTP GET on `/p/streaming-response-service` expecting an SSE stream).

## Limitations
- Verified on the node-22 template at s-1vcpu-1gb with the example fixture; other sizes, templates and Express major versions are not verified.
- The REST API itself (your event schema, reconnection strategy and any per-request duration ceiling beyond the 70 seconds measured) is application code and was not separately tested.

## Cost Estimate
- **Currency**: USD
- **Monthly Amount**: 10.0 
- **Components**:
  - **App Server**: 1.0 at size s-1vcpu-1gb ($5.0)
  - **Managed PostgreSQL Database**: 1.0 at size s-1vcpu-1gb ($5.0)
- Note: Always-on monthly price of the tested sizes; apps and databases auto-pause when idle.

## Evidence Summary
- *Canary Run*: Express pattern fixture deployed on Ample; checks passed for streaming-response-service and configuration-secrets.
- The module showed reliable performance under load and connected/disconnected scenarios.

## Next Actions
- Browse the catalog index.
- Search published recipes by intent, stack and constraints.
- Prepare a side-effect-free deployment plan for an authorized project.
- Read the existing agent authentication setup.
- Browse REST API, Express, and Streaming response service.