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yato

v2.1.6

Published

A node module similar to hystrix. Who caused riots - cut it!

Downloads

33

Readme

yato

Build Status

A node module similar to hystrix. Who caused riots - cut it!

Install

npm install yato

Usage

const Yato = require('yato')
const yato = new Yato({
 // config...
})

yato
  .run(() => Promise.reslove(1))
  .then(data => data === 1) // true

API

run(command, [fallback])

run 函数接受两个参数,第一个参数是要监控的指令,第二个参数是请求失败时需要执行的回退操作。

command 是一个会返回 Promise 的回调函数,在断路器处于非打开状态时,run 函数会返回 command 执行产生的 Promise。

isOpen()

返回当前断路器是否处于打开状态

getStats()

计算并返回当前的统计数据。

{
  "state": "OPEN",
  "latencyMean": 560,
  "percentiles": {
    "25": 200,
    "50": 200,
    "75": 300,
    "90": 500,
    "95": 500,
    "99.5": 500,
    "100": 3000
  },
  "totalCount": 10,
  "errorCount": 7,
  "failures": 6,
  "timeouts": 1,
  "successes": 3,
  "shortCircuits": 0,
  "errorPercentage": 70
}

state -> 表示断路器当前的状态,可能值为: "OPEN", "HALF_OPEN", "CLOSED"

latencyMean -> 平均响应时间 = 总响应时间 / 总请求数

percentiles -> 响应时间百分比,抽取了几个关键数据,上面的例子中表示,50% 的请求延迟在 200ms 以下,75% 的请求延迟在 300ms 以下, 99.5% 的请求延迟在 500ms 以下。总共请求了 10 次的话可以得出,有 5 次请求在 200 ms 以下,有两次在 200 ~ 300ms 之间,有两次在 300ms ~ 500ms 之间,有一次超时请求用了 3000ms。

totalCount -> 总请求次数

errorCount -> 总失败次数 = failures + timeouts

failures -> 请求返回错误次数

timeouts -> 请求超时次数

successes -> 请求成功次数

shortCircuits -> 跳过请求直接返回失败或者 fallback 次数

errorPercentage -> 请求失败率 = errorCount / totalCount

Events

Yato 支持订阅一些重要的事件:

  • open - 断路器被打开时触发
  • close - 断路器被关闭时触发
  • halfOpen - 断路器切换到半打开状态时触发
  • collect - 订阅此事件用来收集统计数据
  yato.on('open', metrics => {
    // metrics: { totalCount, errorCount, failures, successes, timeouts, shortCircuits, errorPercentage }
    console.log(metrics)
  })
  
  yato.on('close', () => {
    console.log('close')
  })
  
  yato.on('halfOpen', () => {
    console.log('halfOpen')
  })
  
  yato.on('collect', stats => {
    // same as getStats API's return.
    console.log(stats)
  })

Config

windowDuration

这个配置十分重要,它决定着一个 bucket 可以存在多久

默认值为 10000,哦对了,这个值的单位是 ms

numBuckets

最多可以存在多少 bucket

默认值为 10

根据 windowDuration 和 numBuckets 可以计算出每隔多久应该产生一个 bucket

timeoutDuration

多久没响应算超时

默认值为 3000,单位也是 ms

errorThreshold

错误率阈值。

出错次数 = 响应出错次数 + 响应超时次数

错误率 = (出错次数 / 请求总次数) * 100

Yato 会在每个请求结束或者超时后,更新断路器的状态,指标之一就是错误率,一旦错误率高于指定的阈值,断路器就会被打开。

默认值为 50

volumeThreshold

请求量阈值。

比如某段时间内,只有一个请求,且这个请求失败或者超时了,我们不希望这个时候就判定该服务 100% 不健康,因此设定了这个选项,只有总请求次数超过了这个值,我们统计的错误率才有意义。

默认值为 5

sleepWindow

窗口睡眠时间,即断路器打开多久后切换为半打开状态

默认值为 5000 ms

关于断路器

buckets => 每隔固定时间产生一个 bucket,每个 bucket 记录这段时间内所有请求的状态, buckets 数量有上限,达到上限后要将最早的 bucket 扔掉

bucket 的产生 => 每隔一段时间产生一个 bucket

state => OPEN / HALF_OPEN / CLOSED

默认状态是 CLOSED,也就是断路器处于关闭状态,请求能够在客户端和服务之间正常传递

每产生一个请求,将请求的情况记录到当前时间所处的 bucket 中,并根据所有的 bucket 的记录计算出服务当前的健康状况,健康状况可以根据不同服务进行配置,默认失败超过请求总量的 50%,会触发断路器打开 —— OPEN,之后的请求看到断路器处于 OPEN 状态,直接返回失败,不再向不健康的服务发送请求,以免其更加不健康。

在断路器开启 OPEN 状态时,启动计时器,根据配置,等待一段时间后,将状态变更为 HALF_OPEN,并允许请求通过,请求结束后根据请求情况更新断路器状态 —— 如果请求失败,则继续 OPEN,再次出发计时器;如果请求成功,变更状态为 CLOSED

Thanks For

https://github.com/Netflix/Hystrix

https://github.com/yammer/circuit-breaker-js

License

MIT