Circuit Breaker examples

README.md

Circuit Breakers

The following examples are for Building a Circuit Breaker in Node.js

CircuitBreaker-configurable.js

class CircuitBreaker {
  constructor(request, options = {}) {
    const defaults = {
      failureThreshold: 3,
      successThreshold: 2,
      timeout: 6000
    }
    Object.assign(this, defaults, options, {
      request,
      state: "CLOSED",
      failureCount: 0,
      successCount: 0,
      nextAttempt: Date.now()
    })
  }

  async fire() {
    if (this.state === "OPEN") {
      if (this.nextAttempt <= Date.now()) {
        this.state = "HALF"
      } else {
        throw new Error("Breaker is OPEN")
      }
    }
    try {
      const response = await this.request()
      return this.success(response)
    } catch (err) {
      return this.fail(err)
    }
  }

  success(response) {
    if (this.state === "HALF") {
      this.successCount++
      if (this.successCount > this.successThreshold) {
        this.successCount = 0
        this.state = "CLOSED"
      }
    }
    this.failureCount = 0

    this.status("Success")
    return response
  }

  fail(err) {
    this.failureCount++
    if (this.failureCount >= this.failureThreshold) {
      this.state = "OPEN"
      this.nextAttempt = Date.now() + this.timeout
    }
    this.status("Failure")
    return err
  }

  status(action) {
    console.table({
      Action: action,
      Timestamp: Date.now(),
      Successes: this.successCount,
      Failures: this.failureCount,
      "Next State": this.state
    })
  }
}

module.exports = CircuitBreaker

CircuitBreaker-manual-overrides.js

class CircuitBreaker {
  constructor(request, options = {}) {
    const defaults = {
      failureThreshold: 3,
      successThreshold: 2,
      timeout: 6000
    }
    Object.assign(this, defaults, options, {
      request,
      state: "CLOSED",
      failureCount: 0,
      successCount: 0,
      nextAttempt: Date.now()
    })
  }
  
  async fire() {
      if (this.state === "OPEN") {
        if (this.nextAttempt <= Date.now()) {
          this.state = "HALF"
        } else {
          throw new Error("Breaker is OPEN")
        }
      }
      try {
        const response = await this.request()
        return this.success(response)
      } catch (err) {
        return this.fail(err)
      }
    }

    success(response) {
      if (this.state === "HALF") {
        this.successCount++
        if (this.successCount > this.successThreshold) {
          this.close()
        }
      }
      this.failureCount = 0

      this.status("Success")
      return response
    }

    fail(err) {
      this.failureCount++
      if (this.failureCount >= this.failureThreshold) {
        this.open()
      }
      this.status("Failure")
      return err
    }

    open() {
      this.state = "OPEN"
      this.nextAttempt = Date.now() + this.timeout
    }
    close() {
      this.successCount = 0
      this.failureCount = 0
      this.state = "CLOSED"
    }
    half() {
      this.state = "HALF"
    }

    status(action) {
      console.table({
        Action: action,
        Timestamp: Date.now(),
        Successes: this.successCount,
        Failures: this.failureCount,
        "Next State": this.state
      })
    }
  }
module.exports = CircuitBreaker

CircuitBreaker-with-fallback.js

class CircuitBreaker {
  constructor(request, options = {}) {
    const defaults = {
      failureThreshold: 3,
      successThreshold: 2,
      timeout: 6000,
      fallback: null
    }
    Object.assign(this, defaults, options, {
      request,
      state: "CLOSED",
      failureCount: 0,
      successCount: 0,
      nextAttempt: Date.now()
    })
  }

  async fire() {
    if (this.state === "OPEN") {
      if (this.nextAttempt <= Date.now()) {
        this.state = "HALF"
      } else {
        if (this.fallback) {
          return this.tryFallback()
        }
        throw new Error("Breaker is OPEN")
      }
    }
    try {
      const response = await this.request()
      return this.success(response)
    } catch (err) {
      return this.fail(err)
    }
  }

  success(response) {
    if (this.state === "HALF") {
      this.successCount++
      if (this.successCount > this.successThreshold) {
        this.successCount = 0
        this.state = "CLOSED"
      }
    }
    this.failureCount = 0

    this.status("Success")
    return response
  }

  fail(err) {
    this.failureCount++
    if (this.failureCount >= this.failureThreshold) {
      this.open()
    }
    this.status("Failure")
    if (this.fallback) return this.tryFallback()
    return err
  }

  open() {
    this.state = "OPEN"
    this.nextAttempt = Date.now() + this.timeout
  }
  close() {
    this.successCount = 0
    this.failureCount = 0
    this.state = "CLOSED"
  }
  half() {
    this.state = "HALF"
  }

  async tryFallback() {
    console.log("Attempting fallback request")
    try {
      const response = await this.fallback()
      return response
    } catch (err) {
      return err
    }
  }

  status(action) {
    console.table({
      Action: action,
      Timestamp: Date.now(),
      Successes: this.successCount,
      Failures: this.failureCount,
      "Next State": this.state
    })
  }
}

module.exports = CircuitBreaker