adding circuitbreaker example using opossum

Author: jkyberneees

demos/circuitbreaker.js

@@ -0,0 +1,59 @@
+const gateway = require('../index')
+const PORT = process.env.PORT || 8080
+const onEnd = require('on-http-end')
+const CircuitBreaker = require('opossum')
+
+const REQUEST_TIMEOUT = 1.5 * 1000
+
+const options = {
+  timeout: REQUEST_TIMEOUT - 200, // If our function takes longer than "timeout", trigger a failure
+  errorThresholdPercentage: 50, // When 50% of requests fail, trip the circuit
+  resetTimeout: 30 * 1000 // After 30 seconds, try again.
+}
+const breaker = new CircuitBreaker(([req, res, url, proxy, proxyOpts]) => {
+  return new Promise((resolve, reject) => {
+    proxy(req, res, url, proxyOpts)
+    onEnd(res, () => {
+      // you can optionally evaluate response codes here...
+      resolve()
+    })
+  })
+}, options)
+
+breaker.fallback(([req, res], err) => {
+  if (err.code === 'EOPENBREAKER') {
+    res.send({
+      message: 'Upps, looks like "public" service is down. Please try again in 30 seconds!'
+    }, 503)
+  }
+})
+
+gateway({
+  routes: [{
+    timeout: REQUEST_TIMEOUT,
+    proxyHandler: (...params) => breaker.fire(params),
+    prefix: '/public',
+    target: 'http://localhost:3000',
+    docs: {
+      name: 'Public Service',
+      endpoint: 'swagger.json',
+      type: 'swagger'
+    }
+  }]
+}).start(PORT).then(() => {
+  console.log(`API Gateway listening on ${PORT} port!`)
+})
+
+const service = require('restana')({})
+service.get('/longop', (req, res) => {
+  setTimeout(() => {
+    res.send('This operation will trigger the breaker failure counter...')
+  }, 2000)
+})
+service.get('/hi', (req, res) => {
+  res.send('Hello World!')
+})
+
+service.start(3000).then(() => {
+  console.log('Public service listening on 3000 port!')
+})