Lazy-load cluster module to fix Passenger

lint fixes

Explicitely cache cluster module

Fix worker listener

Rebase & append CHANGELOG

CHANGELOG.md

@@ -12,6 +12,7 @@ project adheres to [Semantic Versioning](http://semver.org/).
 ### Changed
 
 - Changed `Metric` labelNames & labelValues in TypeScript declaration to a generic type `T extends string`, instead of `string`
+- Lazy-load Node.js Cluster module to fix Passenger support (#293)
 
 ### Added
 

lib/cluster.js

@@ -8,10 +8,16 @@
  * cluster master.
  */
 
-const cluster = require('cluster');
 const Registry = require('./registry');
 const { Grouper } = require('./util');
 const { aggregators } = require('./metricAggregators');
+// We need to lazy-load the 'cluster' module as some application servers -
+// namely Passenger - crash when it is imported.
+let cluster = () => {
+ const data = require('cluster');
+ cluster = () => data;
+ return data;
+};
 
 const GET_METRICS_REQ = 'prom-client:getMetricsReq';
 const GET_METRICS_RES = 'prom-client:getMetricsRes';
@@ -66,11 +72,11 @@ class AggregatorRegistry extends Registry {
  requestId
  };
 
- for (const id in cluster.workers) {
+ for (const id in cluster().workers) {
  // If the worker exits abruptly, it may still be in the workers
  // list but not able to communicate.
- if (cluster.workers[id].isConnected()) {
- cluster.workers[id].send(message);
+ if (cluster().workers[id].isConnected()) {
+ cluster().workers[id].send(message);
  request.pending++;
  }
  }
@@ -153,9 +159,9 @@ function addListeners() {
  if (listenersAdded) return;
  listenersAdded = true;
 
- if (cluster.isMaster) {
+ if (cluster().isMaster) {
  // Listen for worker responses to requests for local metrics
- cluster.on('message', (worker, message) => {
+ cluster().on('message', (worker, message) => {
  if (message.type === GET_METRICS_RES) {
  const request = requests.get(message.requestId);
  message.metrics.forEach(registry => request.responses.push(registry));
@@ -177,17 +183,15 @@ function addListeners() {
  }
 }
 
-if (cluster.isWorker) {
- // Respond to master's requests for worker's local metrics.
- process.on('message', message => {
- if (message.type === GET_METRICS_REQ) {
- process.send({
- type: GET_METRICS_RES,
- requestId: message.requestId,
- metrics: registries.map(r => r.getMetricsAsJSON())
- });
- }
- });
-}
+// Respond to master's requests for worker's local metrics.
+process.on('message', message => {
+ if (cluster().isWorker && message.type === GET_METRICS_REQ) {
+ process.send({
+ type: GET_METRICS_RES,
+ requestId: message.requestId,
+ metrics: registries.map(r => r.getMetricsAsJSON())
+ });
+ }
+});
 
 module.exports = AggregatorRegistry;