Deno Deploy Runtime

Overview

Deno Deploy uses the standard Deno runtime. You can use JSR and NPM packages, filesystem operations, network requests, subprocesses, and FFI/native addons.

Current Environment

• Runtime: Deno 2.5.0
• Platform: Linux (x64 or ARM64)
• Permissions: All permissions enabled automatically (--allow-all)

Note: Custom Deno flags cannot be passed to the runtime.

Serverless Lifecycle

Understanding how your app starts and stops is important for building reliable applications.

Startup

Your application starts when a request arrives. If your app crashes before the HTTP server starts, requests return a 502 error.

Tip: Keep startup fast by:

• Reducing dependencies
• Using dynamic imports for rarely-used code
• Avoiding network requests during startup

Idle Shutdown

After 5-10 minutes without requests:

1. The system sends a SIGINT signal
2. Your app has 5 seconds to shut down gracefully
3. If still running, SIGKILL terminates it

// Handle graceful shutdown
Deno.addSignalListener("SIGINT", () => {
  console.log("Shutting down...");
  // Clean up resources, close connections
  Deno.exit(0);
});

Eviction

Even during active traffic, instances may be terminated due to:

• Infrastructure updates
• Resource constraints

The system redirects traffic first, then signals shutdown. Long-running connections should expect reconnections.

Cold Start Performance

Cold starts typically complete:

• ~100ms for simple "hello world" apps
• A few hundred ms for larger applications

Deno Deploy optimizes cold starts using:

• Pre-provisioned microVMs
• Early TCP connection setup
• File system warmup

Minimizing Cold Start Time

// BAD: Top-level network request delays startup
const config = await fetch("https://api.example.com/config").then((r) =>
  r.json()
);

// GOOD: Lazy load on first request
let config: Config | null = null;
async function getConfig() {
  if (!config) {
    config = await fetch("https://api.example.com/config").then((r) =>
      r.json()
    );
  }
  return config;
}

Limitations

Feature	Status
Custom Deno flags	Not supported
Persistent filesystem	Use Deno KV instead
Long-running background tasks	May be interrupted
System tools	Available but may change

Documentation

• Runtime reference: https://docs.deno.com/deploy/reference/runtime/