A circuit breaker pattern for nodejs. A circuit breaker provides latency and fault protection for distributed systems. Brakes will monitor your outgoing requests, and will trip an internal circuit if it begins to detect that the remote service is beginning to fail. This module is largely based on Netflix's Hystrix

Requires Node 4.2.0 or higher

http://martinfowler.com/bliki/CircuitBreaker.html

https://github.com/Netflix/Hystrix/wiki/How-it-Works

https://en.wikipedia.org/wiki/Circuit_breaker_design_pattern

• Bluebird and Promisify
• Examples
  • Promise
  • Callback
  • Fallback
  • Health Check
• Methods
• Events
• Configuration
• Stats
• Hystrix Dashboard
• Development

Bluebird

This module utilizes bluebird promises. For more on the features of bluebird visit their site: http://bluebirdjs.com/. Brakes uses bluebird over native promises in order to provide more feature rich promises and because bluebird offers performance comparable to that of raw callbacks.

Promisify

If you pass an async function that relies on callback, brakes will promisify it into a bluebird promise. If you pass a promise to brakes, it will use that promise as is.

Note: brakes will only detect async callback functions that use callbacks with one of the following names: cb, callback, callback_, or done.

  function promiseCall(foo){
    return new Promise((resolve, reject) =>{
      if (foo) resolve(foo);
      else reject(foo);
    });
  }

  const brake = new Brakes(promiseCall, {timeout: 150});

  brake.exec('bar')
    .then((result) =>{
      console.log(`result: ${result}`);
    })
    .catch(err =>{
      console.error(`error: ${err}`);
    });

  function asyncCall(foo, cb){
    if (foo) cb(null, foo);
    else cb(new Error(foo));
  }

  const brake = new Brakes(asyncCall, {timeout: 150});

  brake.exec('bar')
    .then((result) =>{
      console.log(`result: ${result}`);
    })
    .catch(err =>{
      console.error(`error: ${err}`);
    });

  function promiseCall(foo){
    return new Promise((resolve, reject) =>{
      if (foo) resolve(foo);
      else reject(foo);
    });
  }

  function fallbackCall(foo){
    return new Promise((resolve, reject) =>{
      resolve('I always succeed');
    });
  }

  const brake = new Brakes(promiseCall, {timeout: 150});

  brake.fallback(fallbackCall)

  brake.exec(false)
    .then((result) =>{
      console.log(`result: ${result}`);
    })
    .catch(err =>{
      console.error(`error: ${err}`);
    });

  function promiseCall(foo){
    return new Promise((resolve, reject) =>{
      if (foo) resolve(foo);
      else reject(foo);
    });
  }

  function fallbackCall(foo){
    return new Promise((resolve, reject) =>{
      resolve('I always succeed');
    });
  }

  function healthCheckCall(foo){
    return new Promise((resolve, reject) => {
      //this will return 20% true, 80% false
      if (Math.random() > 0.8){
        resolve('Health check success');      
      } else {
        reject('Health check failed');
      }
    });
  }

  const brake = new Brakes(promiseCall, {timeout: 150});

  brake.fallback(fallbackCall);

  brake.healthCheck(healthCheckCall);

  brake.exec(false)
    .then((result) =>{
      console.log(`result: ${result}`);
    })
    .catch(err =>{
      console.error(`error: ${err}`);
    });

For a terminal based demonstration:

General Demo npm install && node examples/example1.js

Fallback Demo npm install && node examples/fallback-example.js

Health check Demo npm install && node examples/healthCheck-example.js

Hystrix Stream Demo npm install && node examples/hystrix-example.js

Every brake is an instance of EventEmitter that provides the following events:

• failure: Event on request failure
• success: Event on request success
• timeout: Event on request timeout
• circuitClosed: Event fired when circuit is closed
• circuitOpen: Event fired when circuit is open
• snapshot: Event fired on stats snapshot
• healthCheckFailed: Event fired on failure of each health check execution

Available configuration options.

• name: string to use for name of circuit. This is mostly used for reporting on stats.
• group: string to use for group of circuit. This is mostly used for reporting on stats.
• bucketSpan: time in ms that a specific bucket should remain active
• statInterval: interval in ms that brakes should emit a snapshot event
• percentiles: array<number> that defines the percentile levels that should be calculated on the stats object (i.e. 0.9 for 90th percentile)
• bucketNum: # of buckets to retain in a rolling window
• circuitDuration: time in ms that a circuit should remain broken
• waitThreshold: number of requests to wait before testing circuit health
• threshold: % threshold for successful calls. If the % of successful calls dips below this threshold the circuit will break
• timeout: time in ms before a service call will timeout
• healthCheckInterval: time in ms interval between each execution of health check function
• healthCheck: function to call for the health check (can be defined also with calling healthCheck function)
• fallback: function to call for fallback (can be defined also with calling fallback function)

Based on the opts.statInterval an event will be fired at regular intervals that contains a snapshot of the running state of the application.

// ...
  brake.on('snapshot', snapshot => {
    console.log(`Stats received -> ${snapshot}`);
  });
// ...

Example Stats Object

{ name: 'defaultBrake',
  group: 'defaultBrakeGroup',
  time: 1463297869298,
  circuitDuration: 15000,
  threshold: 0.5,
  waitThreshold: 100,
  stats:
   { failed: 0,
     timedOut: 0,
     total: 249,
     shortCircuited: 0,
     latencyMean: 100,
     successful: 249,
     percentiles:
      { '0': 100,
        '1': 102,
        '0.25': 100,
        '0.5': 100,
        '0.75': 101,
        '0.9': 101,
        '0.95': 102,
        '0.99': 102,
        '0.995': 102 }
    }
  }

Global Stats Stream

Brakes automatically tracks all created instances of brakes and provides a global stats stream for easy consumption and reporting on all brakes instances. These streams will aggregate all stat events into one single stream.

const globalStats = Brakes.getGlobalStats();

globalStats.getRawStream().on('data', (stats) =>{
  console.log('received global stats ->', stats);
});

Using the global stats stream with a special transform, brakes makes it incredibly easy to generate a SSE stream that is compliant with the hystrix dashboard and turbine.

Example:

const globalStats = Brakes.getGlobalStats();

/*
Create SSE Hystrix compliant Server
*/
http.createServer((req, res) => {
  res.setHeader('Content-Type', 'text/event-stream;charset=UTF-8');
  res.setHeader('Cache-Control', 'no-cache, no-store, max-age=0, must-revalidate');
  res.setHeader('Pragma', 'no-cache');
  globalStats.getHystrixStream().pipe(res);
}).listen(8081, () => {
  console.log('---------------------');
  console.log('Hystrix Stream now live at localhost:8081/hystrix.stream');
  console.log('---------------------');
});

To aid in testing it might be useful to have a local instance of the hystrix dashboard running:

docker run -d -p 8080:8080 --name hystrix-dashboard mlabouardy/hystrix-dashboard:latest

Additional Reading: Hystrix Metrics Event Stream, Turbine, Hystrix Dashboard

We gladly welcome pull requests and code contributions. To develop brakes locally clone the repo and use the following commands to aid in development:

npm install
npm run test
npm run test:lint
npm run coverage

Copyright (c) 2016

Permission to use, copy, modify, and/or distribute this software for any purpose with or without fee is hereby granted, provided that the above copyright notice and this permission notice appear in all copies.

THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.