Worker count defaults to CPU core count

lib/cluster.js

@@ -117,6 +117,9 @@ function start(service) {
 
   let workerCount = config.get(`${service.toUpperCase()}_WORKER_PROCESSES`);
 
+  if (!workerCount)
+    workerCount = Math.max(2, require("os").cpus().length);
+
   for (let i = 0; i < workerCount; ++ i)
     cluster.fork();
 }