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.