feat: add prometheusRegistry option (#332)

Added a option prometheusRegistry that allows to pass a existing
prom-client registry.

README.md

@@ -259,6 +259,27 @@ app.use('/metrics', (req, res) => {
 });
 ```
 
+The `prometheusRegistry` option allows to provide a existing 
+[prom-client](https://github.com/siimon/prom-client) registry. 
+The metrics about the circuit will be added to the provided registry instead 
+of the global registry.
+The [default metrics](https://github.com/siimon/prom-client#default-metrics) 
+will not be added to the provided registry.
+
+```js
+const opossum = require('opossum');
+const { Registry } = require('prom-client');
+
+// Create a registry
+const prometheusRegistry = new Registry();
+
+// create a circuit
+const circuit = opossum(functionThatMightFail, {
+  usePrometheus: true,
+  prometheusRegistry
+});
+```
+
 #### Hystrix
 
 **NOTE: Hystrix metrics are deprecated**

lib/circuit.js

@@ -186,7 +186,10 @@ class CircuitBreaker extends EventEmitter {
 
     // Add Prometheus metrics if not running in a web env
     if (PrometheusMetrics && options.usePrometheus) {
-      this[PROMETHEUS_METRICS] = new PrometheusMetrics(this);
+      this[PROMETHEUS_METRICS] = new PrometheusMetrics(
+        this,
+        options.prometheusRegistry
+      );
     }
   }
 

lib/prometheus-metrics.js

@@ -14,19 +14,23 @@ function normalizePrefix(prefixName) {
 }
 
 class PrometheusMetrics {
-  constructor (circuit) {
+  constructor (circuit, registry) {
     this.circuit = circuit;
+    this._registry = registry || client.register
     this._client = client;
     this.counters = [];
     const prefix = normalizePrefix(this.circuit.name);
 
-    this.interval = this._client
-      .collectDefaultMetrics({ prefix, timeout: 5000 });
+    if (!registry) {
+      this.interval = this._client
+        .collectDefaultMetrics({ prefix, timeout: 5000 });
+    }
 
     for (let eventName of this.circuit.eventNames()) {
       const counter = new this._client.Counter({
         name: `${prefix}${eventName}`,
-        help: `A count of the ${circuit.name} circuit's ${eventName} event`
+        help: `A count of the ${circuit.name} circuit's ${eventName} event`,
+        registers: [this._registry]
       });
       this.circuit.on(eventName, _ => {
         counter.inc();
@@ -37,11 +41,11 @@ class PrometheusMetrics {
 
   clear () {
     clearInterval(this.interval);
-    this._client.register.clear();
+    this._registry.clear();
   }
 
   get metrics () {
-    return this._client.register.metrics();
+    return this._registry.metrics();
   }
 
   get client () {

test/prometheus-test.js

@@ -1,46 +1,69 @@
 'use strict';
 
 const test = require('tape');
-const cb = require('../');
+const circuitBreaker = require('../');
 const { passFail } = require('./common');
+const client = require('prom-client');
+
+const { Registry } = client;
 
 test('Factory metrics func does not fail if no circuits yet', t => {
   t.plan(1);
-  t.equal(cb.metrics(), undefined);
+  t.equal(circuitBreaker.metrics(), undefined);
   t.end();
 });
 
 test('A circuit provides prometheus metrics when not in a web env', t => {
   t.plan(1);
-  const circuit = cb(passFail, {usePrometheus: true});
+  const circuit = circuitBreaker(passFail, {usePrometheus: true});
   t.ok(process.env.WEB ? circuit.metrics : !!circuit.metrics);
   circuit.metrics.clear();
   t.end();
 });
 
 test('Does not load Prometheus when the option is not provided', t => {
   t.plan(1);
-  const circuit = cb(passFail);
+  const circuit = circuitBreaker(passFail);
   t.ok(!circuit.metrics);
   circuit.shutdown();
   t.end();
 });
 
 test('The factory function provides access to metrics for all circuits', t => {
   t.plan(4);
-  const c1 = cb(passFail, { usePrometheus: true, name: 'fred' });
-  const c2 = cb(passFail, { usePrometheus: true, name: 'bob' });
+  const c1 = circuitBreaker(passFail, { usePrometheus: true, name: 'fred' });
+  const c2 = circuitBreaker(passFail, { usePrometheus: true, name: 'bob' });
+  t.equal(c1.name, 'fred');
+  t.equal(c2.name, 'bob');
+  t.ok(/circuit_fred_/.test(circuitBreaker.metrics()));
+  t.ok(/circuit_bob_/.test(circuitBreaker.metrics()));
+  t.end();
+});
+
+test('The factory function uses a custom prom-client registry', t => {
+  t.plan(4);
+  const registry = new Registry();
+  const c1 = circuitBreaker(passFail, {
+    usePrometheus: true,
+    name: 'fred',
+    prometheusRegistry: registry
+  });
+  const c2 = circuitBreaker(passFail, {
+    usePrometheus: true,
+    name: 'bob',
+    prometheusRegistry: registry
+  });
   t.equal(c1.name, 'fred');
   t.equal(c2.name, 'bob');
-  t.ok(/circuit_fred_/.test(cb.metrics()));
-  t.ok(/circuit_bob_/.test(cb.metrics()));
+  t.ok(/circuit_fred_/.test(registry.metrics()));
+  t.ok(/circuit_bob_/.test(registry.metrics()));
   t.end();
 });
 
 // All of the additional tests only make sense when running in a Node.js context
 if (!process.env.WEB) {
   test('Circuit fire/success/failure are counted', t => {
-    const circuit = cb(passFail, {usePrometheus: true});
+    const circuit = circuitBreaker(passFail, {usePrometheus: true});
     const fire = /circuit_passFail_fire 2/;
     const success = /circuit_passFail_success 1/;
     const failure = /circuit_passFail_failure 1/;
@@ -59,7 +82,7 @@ if (!process.env.WEB) {
   });
 
   test('Metrics are enabled for all circuit events', t => {
-    const circuit = cb(passFail, {usePrometheus: true});
+    const circuit = circuitBreaker(passFail, {usePrometheus: true});
     const metrics = circuit.metrics.metrics;
     t.plan(circuit.eventNames().length);
     for (let name of circuit.eventNames()) {
@@ -71,7 +94,7 @@ if (!process.env.WEB) {
   });
 
   test('Default prometheus metrics are enabled', t => {
-    const circuit = cb(passFail, {usePrometheus: true});
+    const circuit = circuitBreaker(passFail, {usePrometheus: true});
     const metrics = circuit.metrics.metrics;
     const names = [
       'process_cpu_seconds_total',
@@ -91,8 +114,33 @@ if (!process.env.WEB) {
     t.end();
   });
 
+  test('Should not add default metrics to custom registry', t => {
+    const registry = new Registry();
+    const circuit = circuitBreaker(passFail, {
+      usePrometheus: true,
+      prometheusRegistry: registry
+    });
+    const metrics = circuit.metrics.metrics;
+    const names = [
+      'process_cpu_seconds_total',
+      'process_open_fds',
+      'process_max_fds',
+      'process_virtual_memory_bytes',
+      'process_resident_memory_bytes',
+      'process_heap_bytes',
+      'process_start_time_seconds'
+    ];
+    t.plan(names.length);
+    for (let name of names) {
+      const match = new RegExp(`circuit_passFail_${name}`);
+      t.notOk(match.test(metrics), name);
+    }
+    circuit.metrics.clear();
+    t.end();
+  });
+
   test('Node.js specific metrics are enabled', t => {
-    const circuit = cb(passFail, {usePrometheus: true});
+    const circuit = circuitBreaker(passFail, {usePrometheus: true});
     const metrics = circuit.metrics.metrics;
     const names = [
       'nodejs_eventloop_lag',