circuit-fuses

    4.1.1 • Public • Published

    Circuit-fuses

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    Wrapper around screwdriver-node-circuitbreaker to define a callback interface

    Usage

    npm install circuit-fuses

    This module wraps the screwdriver-node-circuitbreaker and provides a simple callback interface for handling the circuit breaker.

    const Breaker = require('circuit-fuses').breaker;
    const request = require('request');
    const command = request.get
    // To setup the fuse, instantiate a new Breaker with the command to run
    const breaker = new Breaker(command);
    
    breaker.runCommand('http://yahoo.com', (err, resp) => {
        if (err) {
            /* If the circuit is open the command is not run, and an error
             * with message "CircuitBreaker Open" is returned.
             * In this case, you can switch on the error and have a fallback technique
             */
            // ... stuff
        }
        // Here there is no error and it's possible to proceed with the resp object
    });

    The runCommand method will return a promise if a callback is not supplied.

    const Breaker = require('circuit-fuses').breaker;
    const request = require('request');
    const command = request.get
    // To setup the fuse, instantiate a new Breaker with the command to run
    const breaker = new Breaker(command);
    
    breaker.runCommand('http://yahoo.com')
        .then(resp => {
            // Here there is no error and it's possible to proceed with the resp object
        })
        .catch(err => {
            /* If the circuit is open the command is not run, and an error
             * with message "CircuitBreaker Open" is returned.
             * In this case, you can switch on the error and have a fallback technique
             */
            // ... stuff
        });

    Constructor

    constructor(command, options) 

    Parameter Type Required Description Default
    command Function Yes The command to run with circuit breaker none
    options.breaker Object No The object to configure the breaker module with {}
    options.breaker.timeout Number No The timeout in ms to wait for a command 10000
    options.breaker.maxFailures Number No The number of failures before the breaker switches 5
    options.breaker.resetTimeout Number No The number in ms to wait before resetting the circuit 50
    options.retry Object No The object to configure the retry module with {}
    options.retry.retries Number No The number of retries to do before passing back a failure 5
    options.retry.factor Number No The exponential factor to use 2
    options.retry.minTimeout Number No The timeout to wait before doing the first retry 1000
    options.retry.maxTimeout Number No The max timeout to wait before retrying Number.MAX_VALUE
    options.retry.randomize Boolean No Randomize the timeout false
    options.shouldRetry Function No Special logic to should circuit retries () => true

    Short circuiting the retry logic

    Normally, the circuit breaker will retry with exponential back off until the max number of retries has been reached or the breaker has opened due to max failures. You may have operations that you want to immediately fail under certain conditions. In this situation, a shouldRetry option is available. This is a function that receives the err object and arguments passed to the runCommand function.

    For example, short circuit when runCommand is called with "MyArg" and the error contains a status code of 404:

    shouldRetry(err, args) {
        return args[0] === "MyArg" && err.statusCode === 404;
    }

    Run Command

    To run the command passed to the constructor

    runCommand(...args, callback)

    Parameter Type Required Description
    args Arguments No The arguments to pass to the command
    callback Function No The callback to call when the command returns

    Get Total Number Requests

    Returns the total number of requests from the circuit breaker

    getTotalRequests()

    Get Total Number Request Timeouts

    Returns the total number of request timeouts that occurred

    getTimeouts()

    Get Total Number Request Successful

    Returns the total number of successful requests that occurred

    getSuccessfulRequests()

    Get Total Number Request Failed

    Returns the total number of failed requests that occurred

    getFailedRequests()

    Get Total Concurrent Requests

    Returns the total number of concurrent requests that occurred

    getConcurrentRequests()

    Get Average Request time

    Returns the average request time taken

    getAverageRequestTime()

    Get whether the breaker is closed

    Returns boolean whether the circuit breaker is closed

    isClosed()

    Get a holistic set of the above metrics

    stats()

    Using Fuseboxes

    A FuseBox is a collection of circuit breakers. If one circuit breaker in the fuse box breaks, the others break as well. To create a new fusebox:

    const FuseBox = require('circuit-fuses').box;
    const fusebox = new FuseBox();
    

    To add circuit breakers to the fuse box, use the addFuse() method.

    addFuse(circuitbreaker)

    Parameter Type Required Description
    circuitbreaker CircuitBreaker Yes The circuit breaker to add to the fuse box

    Here's an example:

    var breaker1 = new Breaker('testFn');
    var breaker2 = new Breaker('testFn2');
    var breaker3 = new Breaker('testFn3');
    fusebox.addFuse(breaker1);
    fusebox.addFuse(breaker2);
    

    In the above case, if breaker1 trips, breaker2 will trip as well because both of them belong to the same fuse box.

    Testing

    npm test

    License

    Code licensed under the BSD 3-Clause license. See LICENSE file for terms.

    Install

    npm i circuit-fuses

    DownloadsWeekly Downloads

    57

    Version

    4.1.1

    License

    BSD-3-Clause

    Unpacked Size

    18.2 kB

    Total Files

    7

    Last publish

    Collaborators

    • screwdriver
    • nkatzman
    • sd-buildbot