feat: allow to add circuits dynamicaly (nodeshift#7)

* feat: allow to add circuits dynamically

Author: franckOL

README.md

@@ -24,6 +24,11 @@ Example:
   // Provide them to the constructor
   const prometheus = new PrometheusMetrics([c1, c2]);
 
+  //...
+  // Provide other circuit breaker later
+  const c3 = new CircuitBreaker(someOtherfunction3);
+  prometheus.add([C3]);
+  
   // Write metrics to the console
   console.log(prometheus.metrics);
 ```

index.js

@@ -15,12 +15,11 @@ function normalizePrefix (prefixName) {
 
 class PrometheusMetrics {
   constructor (circuits, registry) {
-    if (!circuits) {
-      throw new Error('A circuit or a list of circuits is required');
+    if (circuits instanceof client.Registry) {
+      registry = circuits;
+      circuits = undefined;
     }
 
-    circuits = Array.isArray(circuits) ? circuits : [circuits];
-
     this._registry = registry || client.register;
     this._client = client;
     this.counters = [];
@@ -30,6 +29,16 @@ class PrometheusMetrics {
         .collectDefaultMetrics({ prefix: 'opossum_', timeout: 5000 });
     }
 
+    if (circuits) {
+      this.add(circuits);
+    }
+  }
+
+  add (circuits) {
+    if (!circuits) {
+      return;
+    }
+    circuits = Array.isArray(circuits) ? circuits : [circuits];
     let prefix;
     circuits.forEach(circuit => {
       prefix = normalizePrefix(circuit.name);

test/prometheus-test.js

@@ -20,12 +20,12 @@ function passFail (x) {
   });
 }
 
-test('The factory function errors when no circuits are passed in', t => {
+test('The factory function accept no parameter', t => {
   t.plan(1);
 
-  t.throws(() => {
-    new PrometheusMetrics();
-  }, 'A circuit or a list of circuits is required');
+  const prometheus = new PrometheusMetrics();
+  t.ok(prometheus);
+  prometheus.clear();
 
   t.end();
 });
@@ -73,6 +73,43 @@ test('The factory function uses a custom prom-client registry', t => {
   t.end();
 });
 
+test('The add function takes an object instead of just an Array', t => {
+  t.plan(2);
+  const c1 = new CircuitBreaker(passFail, { name: 'fred' });
+  const prometheus = new PrometheusMetrics();
+  prometheus.add(c1);
+  t.equal(c1.name, 'fred');
+  t.ok(/circuit_fred_/.test(prometheus.metrics));
+  prometheus.clear();
+  t.end();
+});
+
+test('The add function provides access to metrics for all circuits', t => {
+  t.plan(6);
+  const c1 = new CircuitBreaker(passFail, { name: 'fred' });
+  const c2 = new CircuitBreaker(passFail, { name: 'bob' });
+  const c3 = new CircuitBreaker(passFail, { name: 'foo' });
+  const prometheus = new PrometheusMetrics([c1]);
+  prometheus.add([c2, c3]);
+  t.equal(c1.name, 'fred');
+  t.equal(c2.name, 'bob');
+  t.equal(c3.name, 'foo');
+  t.ok(/circuit_fred_/.test(prometheus.metrics));
+  t.ok(/circuit_bob_/.test(prometheus.metrics));
+  t.ok(/circuit_foo_/.test(prometheus.metrics));
+  prometheus.clear();
+  t.end();
+});
+
+test('The add function accepts zero parameters', t => {
+  t.plan(1);
+  const prometheus = new PrometheusMetrics();
+  prometheus.add();
+  t.notOk(/circuit_/.test(prometheus.metrics));
+  prometheus.clear();
+  t.end();
+});
+
 test('Circuit fire/success/failure are counted', t => {
   const circuit = new CircuitBreaker(passFail);
   const fire = /circuit_passFail_fire 2/;
@@ -150,6 +187,38 @@ test('Should not add default metrics to custom registry', t => {
   t.end();
 });
 
+test('Default prometheus metrics are enabled without circuit', t => {
+  const registry = new Registry();
+  const prometheus = new PrometheusMetrics(registry);
+  const metrics = prometheus.metrics;
+  const names = [
+    'nodejs_eventloop_lag',
+    'nodejs_active_handles',
+    'nodejs_active_requests',
+    'nodejs_heap_size_total_bytes',
+    'nodejs_heap_size_used_bytes',
+    'nodejs_external_memory_bytes',
+    'nodejs_heap_space_size_total_bytes',
+    'nodejs_heap_space_size_used_bytes',
+    'nodejs_heap_space_size_available_bytes',
+    'nodejs_version_info',
+    '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 (const name of names) {
+    const match = new RegExp(`opossum_${name}`);
+    t.notOk(match.test(metrics), name);
+  }
+  prometheus.clear();
+  t.end();
+});
+
 test('Node.js specific metrics are enabled', t => {
   const circuit = new CircuitBreaker(passFail);
   const prometheus = new PrometheusMetrics([circuit]);