Improve streaming server with cluster (#1970)

.env.production.sample

@@ -81,3 +81,7 @@ SMTP_FROM_ADDRESS=notifications@example.com
 # Advanced settings
 # If you need to use pgBouncer, you need to disable prepared statements:
 # PREPARED_STATEMENTS=false
+
+# Cluster number setting for streaming API server.
+# If you comment out following line, cluster number will be `numOfCpuCores - 1`.
+STREAMING_CLUSTER_NUM=1

streaming/index.js

@@ -1,3 +1,5 @@
+import os from 'os';
+import cluster from 'cluster';
 import dotenv from 'dotenv'
 import express from 'express'
 import http from 'http'
@@ -14,6 +16,23 @@ dotenv.config({
   path: env === 'production' ? '.env.production' : '.env'
 })
 
+if (cluster.isMaster) {
+  // cluster master
+
+  const core = +process.env.STREAMING_CLUSTER_NUM || (env === 'development' ? 1 : os.cpus().length - 1)
+  const fork = () => {
+    const worker = cluster.fork();
+    worker.on('exit', (code, signal) => {
+      log.error(`Worker died with exit code ${code}, signal ${signal} received.`);
+      setTimeout(() => fork(), 0);
+    });
+  };
+  for (let i = 0; i < core; i++) fork();
+  log.info(`Starting streaming API server master with ${core} workers`)
+
+} else {
+  // cluster worker
+
   const pgConfigs = {
     development: {
       database: 'mastodon_development',
@@ -309,5 +328,6 @@ wss.on('connection', ws => {
 
   server.listen(process.env.PORT || 4000, () => {
     log.level = process.env.LOG_LEVEL || 'verbose'
-  log.info(`Starting streaming API server on port ${server.address().port}`)
+    log.info(`Starting streaming API server worker on port ${server.address().port}`)
   })
+}