Brakes is a circuit breaker library for Node. 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 failing. Circuit protection allows you to redirect requests to sane fallbacks, and back-off the downstream services so they can recover. 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
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}`);
});Brakes exposes the ability to create a main Brakes instance that can then contain subCircuits that all report to a central stats object. This allows all subCircuits to be tripped at the same time when the overall health of all the subCircuits crosses a defined threshold.
See examples/sub-circuit.js for a more complete example.
function promiseCall(foo){
return new Promise((resolve, reject) =>{
if (foo) resolve(foo);
else reject(foo);
});
}
const brake = new Brakes({
timeout: 150,
fallback: () => Promise.resolve('Response from fallback'),
});
const subCircuit1 = brake.subCircuit(promiseCall);
const subCircuit2 = brake.subCircuit(promiseCall);
subCircuit1.exec('bar')
.then((result) =>{
console.log(`result: ${result}`);
})
.catch(err =>{
console.error(`error: ${err}`);
});
// all stats are reported through the main brakes instance
brake.on('snapshot', snapshot => {
console.log(`Stats received -> ${snapshot}`);
});
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
Sub Circuits
npm install && node examples/sub-circuit.js
| Method | Argument(s) | Returns | Description |
|---|---|---|---|
| getGlobalStats | N/A | globalStats | Returns a reference to the global stats tracker |
| static getGlobalStats | N/A | globalStats | Returns a reference to the global stats tracker |
| exec | N/A | Promise | Executes the circuit |
| fallback | function (must return promise or accept callback) | N/A | Registers a fallback function for the circuit |
| healthCheck | function (must return promise or accept callback) | N/A | Registers a health check function for the circuit |
| subCircuit | function (required), function (optional), opts (optional) | N/A | Create a new sub circuit that rolls up into the main circuit it is created under. |
| on | eventName, function | N/A | Register an event listener |
| destroy | N/A | N/A | Removes all listeners and deregisters with global stats tracker. |
| isOpen | N/A | boolean | Returns true if circuit is open |
Every brake is an instance of EventEmitter that provides the following events:
- exec: Event on request start
- 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:
stringto use for name of circuit. This is mostly used for reporting on stats. - group:
stringto use for group of circuit. This is mostly used for reporting on stats. - bucketSpan: time in
msthat a specific bucket should remain active - statInterval: interval in
msthat brakes should emit asnapshotevent - 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
msthat a circuit should remain broken - waitThreshold:
numberof 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
msbefore a service call will timeout - isFailure: function that returns true if an error should be considered a failure (receives the error object returned by your command.) This allows for non-critical errors to be ignored by the circuit breaker
- healthCheckInterval: time in
msinterval between each execution of health check function - healthCheck: function to call for the health check (can be defined also with calling
healthCheckfunction) - fallback: function to call for fallback (can be defined also with calling
fallbackfunction) - isPromise:
booleanto opt out of check for callback in function. This affects the passed in function, health check and fallback - isFunction:
booleanto opt out of check for callback, always promisifying in function. This affects the passed in function, health check and fallback - modifyError: modifies the error message by adding circuit name. default is true.
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 -p 9002:9002 --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
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