Start a cluster of HTTP servers | Bun 日本語

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.

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");
  },
});

Note

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

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.