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| 'use strict' | ||
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| /** | ||
| * Copyright 2016-present, Dustin Deus (deusdustin@gmail.com) | ||
| * All rights reserved. | ||
| * | ||
| * This source code is licensed under the MIT-style license found in the | ||
| * LICENSE file in the root directory of this source tree. | ||
| * | ||
| */ | ||
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| const EventEmitter = require('events') | ||
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| /** | ||
| * Based on https://docs.microsoft.com/en-us/azure/architecture/patterns/circuit-breaker | ||
| * | ||
| * @class CircuitBreaker | ||
| * @extends {EventEmitter} | ||
| */ | ||
| class CircuitBreaker extends EventEmitter { | ||
| constructor (options) { | ||
| super() | ||
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| // states | ||
| this.CIRCUIT_CLOSE = 'close' | ||
| this.CIRCUIT_HALF_OPEN = 'half_open' | ||
| this.CIRCUIT_OPEN = 'open' | ||
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| // intial state | ||
| this._state = this.CIRCUIT_CLOSE | ||
| // current fauilures | ||
| this._failureCount = 0 | ||
| // successes count | ||
| this._successesCount = 0 | ||
| // max failure threshold | ||
| this._maxFailures = options.maxFailures | ||
| // min successes to close the circuit breaker | ||
| this._minSuccesses = options.minSuccesses | ||
| // the timeout when the circuit breaker in in half open state | ||
| this._halfOpenTime = options.halfOpenTime | ||
| // interval when the circuit breaker will reset | ||
| this._resetIntervalTime = options.resetIntervalTime | ||
| // half open timer | ||
| this._failureTimer = null | ||
| } | ||
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| /** | ||
| * | ||
| * | ||
| * @readonly | ||
| * | ||
| * @memberof CircuitBreaker | ||
| */ | ||
| get state () { | ||
| return this._state | ||
| } | ||
| /** | ||
| * The failure counter used by the Closed state is time based. It's automatically reset at periodic intervals. | ||
| * This helps to prevent the circuit breaker from entering the Open state if it experiences occasional failures | ||
| * | ||
| * | ||
| * @memberof CircuitBreaker | ||
| */ | ||
| startResetInterval () { | ||
| this._resetInterval = setInterval(() => { | ||
| this._state = this.CIRCUIT_CLOSE | ||
| }, this._resetIntervalTime) | ||
| } | ||
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| /** | ||
| * | ||
| * | ||
| * | ||
| * @memberof CircuitBreaker | ||
| */ | ||
| clearHalfOpenTimer () { | ||
| if (this._halfOpenTime) { | ||
| clearTimeout(this._halfOpenTime) | ||
| } | ||
| } | ||
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| /** | ||
| * | ||
| * | ||
| * | ||
| * @memberof CircuitBreaker | ||
| */ | ||
| startHalfOpenTimer () { | ||
| this._halfOpenTimer = setTimeout(() => { | ||
| this._successesCount = 0 | ||
| this._state = this.CIRCUIT_HALF_OPEN | ||
| }, this._halfOpenTime) | ||
| // unref from event loop | ||
| this._halfOpenTimer.unref() | ||
| } | ||
| /** | ||
| * | ||
| * | ||
| * | ||
| * @memberof CircuitBreaker | ||
| */ | ||
| clearResetInterval () { | ||
| if (this._resetInterval) { | ||
| clearInterval(this._resetInterval) | ||
| } | ||
| } | ||
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| /** | ||
| * | ||
| * | ||
| * @returns | ||
| * | ||
| * @memberof CircuitBreaker | ||
| */ | ||
| available () { | ||
| return this._state !== this.CIRCUIT_OPEN | ||
| } | ||
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| /** | ||
| * | ||
| * | ||
| * | ||
| * @memberof CircuitBreaker | ||
| */ | ||
| success () { | ||
| this.check(true) | ||
| } | ||
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| /** | ||
| * | ||
| * | ||
| * | ||
| * @memberof CircuitBreaker | ||
| */ | ||
| failure () { | ||
| this.check(false) | ||
| } | ||
| /** | ||
| * | ||
| * | ||
| * @param {any} pattern | ||
| * @returns | ||
| * | ||
| * @memberof CircuitBreaker | ||
| */ | ||
| check (success) { | ||
| if (this._state === this.CIRCUIT_HALF_OPEN) { | ||
| // The counter used by the Half-Open state records the number of successful attempts to invoke the operation. | ||
| // The circuit breaker reverts to the Closed state after a specified number of consecutive operation invocations have been successful. | ||
| if (success === true) { | ||
| if (this._successesCount >= this._minSuccesses) { | ||
| this._state = this.CIRCUIT_CLOSE | ||
| this.emit('stateChange', { state: this.CIRCUIT_CLOSE }) | ||
| } | ||
| this._successesCount += 1 | ||
| this.emit('success', { count: this._successesCount }) | ||
| } else if (success === false) { | ||
| // If any invocation fails, the circuit breaker enters the Open state immediately and | ||
| // the success counter will be reset the next time it enters the Half-Open state. | ||
| this._state = this.CIRCUIT_OPEN | ||
| this._failureCount = 0 | ||
| this.clearHalfOpenTimer() | ||
| this.emit('stateChange', { state: this.CIRCUIT_OPEN }) | ||
| } | ||
| } else if (this._state === this.CIRCUIT_OPEN) { | ||
| this._failureCount = 0 | ||
| // At this point the proxy starts a timeout timer | ||
| // and when this timer expires the proxy is placed into the Half-Open state. | ||
| this.startHalfOpenTimer() | ||
| this.emit('stateChange', { state: this.CIRCUIT_HALF_OPEN }) | ||
| } else if (this._state === this.CIRCUIT_CLOSE) { | ||
| // when request fails we increment the failureCount | ||
| if (success === false) { | ||
| this._failureCount += 1 | ||
| this.emit('failure', { count: this._failureCount }) | ||
| } | ||
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| // when we reach maximum failure threshold we open the circuit breaker and start the reset timer | ||
| if (this._failureCount >= this._maxFailures) { | ||
| this._state = this.CIRCUIT_OPEN | ||
| this.clearResetInterval(this._resetInterval) | ||
| this.startResetInterval() | ||
| this.emit('stateChange', { state: this.CIRCUIT_OPEN }) | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
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| module.exports = CircuitBreaker |
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