Add cluster support to multiply outbound write throughput

cluster.js

@@ -0,0 +1,44 @@
+const cluster = require('cluster');
+
+if (cluster.isPrimary) {
+  const requested = parseInt(process.env.WEB_CONCURRENCY, 10);
+  const workers = Number.isInteger(requested) && requested > 0 ? requested : 4;
+  console.log(`Primary ${process.pid} starting ${workers} workers`);
+  for (let i = 0; i < workers; i++) fork();
+
+  // resurrect a worker if it dies, unless we're shutting down, also track fast crashes and exit if too many happen in a row
+  let shuttingDown = false;
+  let fastCrashes = 0;
+  cluster.on('exit', (worker, code, signal) => {
+    if (shuttingDown) return;
+    const ranForMs = Date.now() - worker.startedAt;
+    if (ranForMs < 5000) {
+      fastCrashes++;
+      console.error(`Worker ${worker.process.pid} died after ${ranForMs}ms (${signal || code}) [fast-crash ${fastCrashes}/${workers}]`);
+      if (fastCrashes >= workers) {
+        console.error('Too many fast worker crashes; exiting for the service manager to restart.');
+        process.exit(1);
+      }
+    } else {
+      fastCrashes = 0; // a healthy run clears the streak
+      console.log(`Worker ${worker.process.pid} died after ${Math.round(ranForMs / 1000)}s (${signal || code}); respawning`);
+    }
+    fork();
+  });
+
+  for (const sig of ['SIGTERM', 'SIGINT']) {
+    process.on(sig, () => {
+      shuttingDown = true;
+      for (const w of Object.values(cluster.workers)) w.kill(sig);
+    });
+  }
+} else {
+  // equivalent to `probot run ./index.js` (app path passed as a positional arg)
+  require('probot').run([process.argv[0], process.argv[1], './index.js']);
+}
+
+function fork() {
+  const worker = cluster.fork();
+  worker.startedAt = Date.now();
+  return worker;
+}

package.json

@@ -9,9 +9,10 @@
   "license": "ISC",
   "repository": "https://github.com/stilliard/github-task-list-completed.git",
   "scripts": {
-    "dev-debug": "nodemon --exec \"LOG_LEVEL=debug npm start\"",
-    "dev": "nodemon --exec \"npm start\"",
-    "start": "probot run ./index.js",
+    "dev-debug": "nodemon --exec \"LOG_LEVEL=debug npm run start:single\"",
+    "dev": "nodemon --exec \"npm run start:single\"",
+    "start": "node cluster.js",
+    "start:single": "probot run ./index.js",
     "test": "jest"
   },
   "dependencies": {