circuit breaker example using opossum js

opossum-example.js

const Promise = require('bluebird');
const CircuitBreaker = require('opossum');

// need a logger
const log = require('bunyan').createLogger({ name: 'example' });

// mock sla
const mockService = sla => () => (Math.random() > (1 - sla) ? Promise.resolve('foo bar') : Promise.delay(3000));

// create circuit breaker
const getFooBreaker = new CircuitBreaker(mockService(0.95), {
  timeout: 1000, //mockService will can timeout when got delay
  errorThresholdPercentage: 10, // When 10% of requests fail, trip the circuit
  resetTimeout: 3000, // After 3s, try again.
});

// fallback?
// getFooBreaker.fallback(() => Promise.resolve('We always prevail!'));
// getFooBreaker.on('fallback', () => log.info('fallback hit!'))

// healthcheck always on!
getFooBreaker.healthCheck(() => Promise.delay(500).tap(() => log.info('health check!')));

// counter for sla
let counter = 0, counter_error = 0;
setInterval(() => {
  counter++;
  if (counter % 100 === 0) {
    let sla = (100 - (counter_error / counter * 100)).toFixed(2) + '%'
    log.info({counter, counter_error, sla});
  }

  // fire request
  getFooBreaker
    .fire()
    .then(() => null)
    .catch(() => ++counter_error)
}, 20); // every .2s