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circuit-fuses

Circuit-fuses

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Wrapper around node-circuitbreaker to define a callback interface

Usage

npm install circuit-fuses

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

const Breaker = require('circuit-fuses');
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');
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()

Testing

npm test

License

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