Bu yazı aslında Fault Tolerance ve Resiliency İçin Bazı Yazılım Çözümleri serisinin bir parçası.
Bu yöntem microservice mimarisinde kullanılıyor. Eğer bir sistem cevap vermiyorsa ona sürekli erişmeye çalışmak yerine sigorta (circuit breaker) devreye girer ve direkt hata mesajı/kodu döndürür. Açıklaması şöyle.
In a nutshell — Do not hammer a service with additional requests which is already down. Please give the service time to recover.Açıklaması şöyle.
Circuit Breaker monitors API calls. When everything is working as expected, it is in the state closed. When the number of fails, like timeout, reaches a specified threshold, Circuit Breaker will stop processing further requests. We call it the open state. As a result, API clients will receive instant information that something went wrong without waiting for the timeout to come.
The Circuit is opened for a specified period of time. After timeout occurs, the circuit breaker goes into the half-opened state. Next, the API call will hit the external system/API. After that, the circuit will decide whether to close or open itself.
Sigorta 3 durumda olabilir. Şeklen şöyle
CLOSED Durumu - Her şey Yolunda
Açıklaması şöyle. Belli bir sayıda hata aldıktan sonra OPEN durumuna geçer.
The circuit breaker being in a CLOSED state means that everything is working fine and all calls pass through to the remote services. Once the number of failures exceeds a predetermined threshold, the circuit breaker trips and enters into the open state.
OPEN Durumu - Sigorta Atmıştır
Açıklaması şöyle. Direkt hata kodu döndürür. Belli bir süre sonra HALF-OPEN durumuna geçiş yapılır
Once the number of timeouts reaches a predetermined threshold in the circuit breaker, it trips the circuit breaker to the OPEN state. In the OPEN state, the circuit breaker returns an error for all calls to the service without making the calls to the remote service.
HALF-OPEN Durumu
Açıklaması şöyle. Halen hata kodu döndürür, ancak servisleri kontrol etmek için deneme çağrıları yapar.
After a certain duration, the circuit switches to a HALF-OPEN state to test if the underlying problem still exists. The circuit breaker uses a mechanism to make a trial call to the remote service periodically to check if it has recovered. If the call to the Remote service fails, the circuit breaker remains in the OPEN state. If the call returns success, then the circuit switches to the CLOSED state.
State Geçişi
Açıklaması şöyle
There are 2 types of circuit breaker patterns, Count-based and Time-based.1. Count-based: the circuit breaker switches from a closed state to an open state when the last N requests have failed or timeout.2. Time-based: the circuit breaker switches from a closed state to an open state when the last N time unit has failed or timeout.In both types of circuit breakers, we can determine what the threshold for failure or timeout is. Suppose we specify that the circuit breaker will trip and go to the Open state when 50% of the last 20 requests took more than 2s, or for a time-based, we can specify that 50% of the last 60 seconds of requests took more than 5s.After we know how the circuit breaker works, then we will try to implement it in the spring boot project.
Circuit Breaker Kütüphaneleri
- Netflix’s Hystrix
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