doc: update readme with prometheus information

Fixes: #329

README.md

@@ -237,7 +237,31 @@ Typings are available [here](https://github.com/DefinitelyTyped/DefinitelyTyped/
 
 If you'd like to add them, run `npm install @types/opossum` in your project.
 
-### Hystrix Metrics
+### Metrics
+
+#### Prometheus
+Provide `{ usePrometheus: true }` in the options when creating a circuit to produce
+metrics that are consumable by Prometheus. These metrics include information about
+the circuit itself, for example how many times it has opened, as well as general Node.js
+statistics, for example event loop lag. To get consolidated metrics for all circuits in your
+application, use the `metrics()` function on the factory. 
+
+```js
+const opossum = require('opossum');
+
+// create a circuit
+const circuit = opossum(functionThatMightFail, { usePrometheus: true });
+
+// In an express app, expose the metrics to the Prometheus server
+app.use('/metrics', (req, res) => {
+  res.type('text/plain');
+  res.send(opossum.metrics());
+});
+```
+
+#### Hystrix
+
+**NOTE: Hystrix metrics are deprecated**
 
 A Hystrix Stream is available for use with a Hystrix Dashboard using the `circuitBreaker.hystrixStats.getHystrixStream` method.
 

docs/index.html

@@ -55,6 +55,16 @@ <h3 class='mb0 no-anchor'>opossum</h3>
                 </li>
 
 
+                <li><a
+                  href='#factorymetrics'
+                  class="">
+                  factory.metrics
+
+                </a>
+
+                </li>
+
+
                 <li><a
                   href='#circuitbreaker'
                   class=" toggle-sibling">
@@ -654,7 +664,25 @@ <h3>Promises vs. Callbacks</h3>
 <h3>Typings</h3>
 <p>Typings are available <a href="https://github.com/DefinitelyTyped/DefinitelyTyped/tree/master/types/opossum">here</a>.</p>
 <p>If you'd like to add them, run <code>npm install @types/opossum</code> in your project.</p>
-<h3>Hystrix Metrics</h3>
+<h3>Metrics</h3>
+<h4>Prometheus</h4>
+<p>Provide <code>{ usePrometheus: true }</code> in the options when creating a circuit to produce
+metrics that are consumable by Prometheus. These metrics include information about
+the circuit itself, for example how many times it has opened, as well as general Node.js
+statistics, for example event loop lag. To get consolidated metrics for all circuits in your
+application, use the <code>metrics()</code> function on the factory. </p>
+<pre class='hljs'><span class="hljs-keyword">const</span> opossum = <span class="hljs-built_in">require</span>(<span class="hljs-string">'opossum'</span>);
+
+<span class="hljs-comment">// create a circuit</span>
+<span class="hljs-keyword">const</span> circuit = opossum(functionThatMightFail, { <span class="hljs-attr">usePrometheus</span>: <span class="hljs-literal">true</span> });
+
+<span class="hljs-comment">// In an express app, expose the metrics to the Prometheus server</span>
+app.use(<span class="hljs-string">'/metrics'</span>, (req, res) =&gt; {
+  res.type(<span class="hljs-string">'text/plain'</span>);
+  res.send(opossum.metrics());
+});</pre>
+<h4>Hystrix</h4>
+<p><strong>NOTE: Hystrix metrics are deprecated</strong></p>
 <p>A Hystrix Stream is available for use with a Hystrix Dashboard using the <code>circuitBreaker.hystrixStats.getHystrixStream</code> method.</p>
 <p>This method returns a <a href="https://nodejs.org/api/stream.html">Node.js Stream</a>, which makes it easy to create an SSE stream that will be compliant with a Hystrix Dashboard.</p>
 <p>Additional Reading: <a href="https://github.com/Netflix/Hystrix/tree/master/hystrix-contrib/hystrix-metrics-event-stream">Hystrix Metrics Event Stream</a>, <a href="https://github.com/Netflix/Turbine/wiki">Turbine</a>, <a href="https://github.com/Netflix/Hystrix/wiki/Dashboard">Hystrix Dashboard</a></p>
@@ -1005,6 +1033,62 @@ <h3 class='fl m0' id='factorypromisify'>
 
 
 
+</section>
+
+
+
+
+          <section class='p2 mb2 clearfix bg-white minishadow'>
+
+
+  <div class='clearfix'>
+
+    <h3 class='fl m0' id='factorymetrics'>
+      factory.metrics
+    </h3>
+
+
+  </div>
+
+
+  <p>Get the Prometheus metrics for all circuits.</p>
+
+    <div class='pre p1 fill-light mt0'>factory.metrics(): <a href="https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/String">String</a></div>
+
+
+
+
+
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+
+
+
+      <div class='py1 quiet mt1 prose-big'>Returns</div>
+      <code><a href="https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/String">String</a></code>:
+        the metrics for all circuits
+
+
+
+
+
+
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+
+
 </section>