Start a cluster of HTTP servers

To run multiple HTTP servers concurrently, use the reusePort option in Bun.serve(). It shares one port across multiple processes, and incoming requests are load balanced across them.

server.ts

import { serve } from "bun";

const id = Math.random().toString(36).slice(2);

serve({
  port: process.env.PORT || 8080,
  development: false,

  // Share the same port across multiple processes
  // This is the important part!
  reusePort: true,

  async fetch(request) {
    return new Response("Hello from Bun #" + id + "!\n");
  },
});

Linux only — Windows and macOS ignore the reusePort option. This is an operating system limitation with SO_REUSEPORT.

After saving the file, start your servers on the same port. reusePort uses the Linux SO_REUSEPORT and SO_REUSEADDR socket options to ensure fair load balancing across processes. Learn more about SO_REUSEPORT and SO_REUSEADDR

cluster.ts

import { spawn } from "bun";

const cpus = navigator.hardwareConcurrency; // Number of CPU cores
const buns = new Array(cpus);

for (let i = 0; i < cpus; i++) {
  buns[i] = spawn({
    cmd: ["bun", "./server.ts"],
    stdout: "inherit",
    stderr: "inherit",
    stdin: "inherit",
  });
}

function kill() {
  for (const bun of buns) {
    bun.kill();
  }
}

process.on("SIGINT", kill);
process.on("exit", kill);

Bun also implements the node:cluster module; reusePort is a faster but more limited alternative.

Hot reload an HTTP server

Configure TLS on an HTTP server