Introduction

Circuit break is used to degrade a resource when it is in an unstable state. There are two ways to determine whether a resource is in a stable state:

  • Average Response Time ('DegradeRule.Grade=RuleContants.DEGRADE_RT'): When the average RT exceeds the threshold ('count' in 'DegradeRule', ms), the resource enters a quasi-degraded state. If the RT of next coming five requests still exceeds this threshold, this resource will be degraded, which means that in the next time window(Defined in 'timeWindow', s units) all the access to this resource will be blocked.
  • Exception ratio: Exception ratio= Exception count per second/Success QPS. When the ratio exceeds the threshold, access to the resource will be blocked in the specified time window.

    Demo

Run the demo and the output will be as follows:

  1.  1529399827825,total:0, pass:0, block:0
  2.  1529399828825,total:4263, pass:100, block:4164  
  3.  1529399829825,total:19179, pass:4, block:19176
  4.  1529399830824,total:19806, pass:0, block:19806  //begin degrade
  5.  1529399831825,total:19198, pass:0, block:19198  
  6.  1529399832824,total:19481, pass:0, block:19481
  7.  1529399833826,total:19241, pass:0, block:19241
  8.  1529399834826,total:17276, pass:0, block:17276
  9.  1529399835826,total:18722, pass:0, block:18722
  10.  1529399836826,total:19490, pass:0, block:19492
  11.  1529399837828,total:19355, pass:0, block:19355
  12.  1529399838827,total:11388, pass:0, block:11388
  13.  1529399839829,total:14494, pass:104, block:14390 //After 10 seconds, the system is restored, and degraded very quickly
  14.  1529399840854,total:18505, pass:0, block:18505
  15.  1529399841854,total:19673, pass:0, block:19676

原文: https://github.com/alibaba/Sentinel/wiki/Circuit-Break