page:recipes:mobile backend:express:response streaming

Host mobile backend with Express: streamed responses

Deploy a mobile backend 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 mobile backend-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: the observed behavior matches the aforementioned expectations. 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 routes and 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: GET / expects output ample canary express patterns.
• Streaming response service self-test: GET /p/streaming-response-service expects a Server-Sent Events stream behavior as described.

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 mobile backend-specific behavior is not separately tested; the pattern checks are what was verified.
• Managed PostgreSQL 16 only; extensions, connection limits and backup or restore procedures are not verified.

Cost Estimate

• Currency: USD
• Monthly Amount: 10.0
• Components:
  • App server: s-1vcpu-1gb, quantity: 1, monthly amount: 5.0
  • Managed PostgreSQL database: s-1vcpu-1gb, quantity: 1, monthly amount: 5.0
• Note: Always-on monthly price; 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.
  • Observed At: 2026-09-21T02:34:39Z
  • Implementation Revision: 1d28ae0-dirty (CLI 0.1.21)
• Canary run: Same Express app deployed with a --release-command migration.
  • Observed At: 2026-09-20T01:54:51Z

Next Actions

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