ansarizafar · April 26, 2025 05:53 · Apr 25, 2025
diff --git a/clustered.ts b/clustered.ts
@@ -0,0 +1,86 @@
+import cluster from "node:cluster"; 
+import { availableParallelism } from "node:os";
+
+export async function clustered({
+    numWorkers = availableParallelism(),
+    primary,
+    worker,
+    recoverWorkers = true,
+    shutdownPrimary,
+  }: {
+    numWorkers?: number;
+    primary?: () => Promise<void>;
+    worker: () => Promise<void>;
+    recoverWorkers?: boolean;
+    shutdownPrimary?: () => Promise<void>;
+  }) {
+    if (cluster.isPrimary) {
+      process.on("SIGHUP", () => {
+        console.info("SIGHUP");
+        const workersAtSighup = Object.values(cluster.workers || {}).filter(
+          (worker) => worker?.isConnected()
+        );
+        for (const worker of workersAtSighup) {
+          const newWorker = cluster.fork();
+          newWorker.on("listening", () => {
+            console.info(`killing worker ${worker?.process.pid}`);
+            worker?.disconnect();
+          });
+        }
+      });
+
+      const shutdown = async () => {
+        for (const worker of Object.values(cluster.workers || {})) {
+          worker?.disconnect();
+        }
+
+        if (shutdownPrimary) {
+          await shutdownPrimary();
+        }
+
+        console.log("exiting now");
+        process.exit(0);
+      };
+
+      // eslint-disable-next-line @typescript-eslint/no-misused-promises
+      process.on("SIGTERM", async () => {
+        console.info("SIGTERM");
+        await shutdown();
+      });
+
+      // eslint-disable-next-line @typescript-eslint/no-misused-promises
+      process.on("SIGINT", async () => {
+        console.info("SIGINT");
+        await shutdown();
+      });
+
+      // Fork
+      for (let i = 0; i < numWorkers; i++) {
+        cluster.fork();
+      }
+
+      if (recoverWorkers) {
+        cluster.on("exit", (worker, code, signal) => {
+          // we did this on purpose, so we don't need to restart the worker
+          if (worker.exitedAfterDisconnect) {
+            console.info(
+              `worker ${worker.process.pid} exited after disconnect. not restarting.`
+            );
+            return;
+          }
+          console.info(
+            { worker_pid: worker.process.pid, signal, code },
+            "worker exited, restarting..."
+          );
+          cluster.fork();
+        });
+      }
+
+      if (primary) {
+        await primary();
+      }
+    } else {
+      await worker();
+    }
+  }
+
diff --git a/index.ts b/index.ts
@@ -0,0 +1,18 @@
+import { createServer } from "node:http";
+import { clustered } from "./clustered.ts";
+
+const server = createServer((req, res) => {
+  res.writeHead(200, { "Content-Type": "text/plain" });
+  res.end("Hello, World!\n");
+});
+
+await clustered({
+  numWorkers: 3,
+  primary: async () => {
+    console.log("primary started!", process.pid);
+  },
+  worker: async () => {
+    console.log("worker started!", process.pid);
+    server.listen(3000);
+  },
+});