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I am trying to understand Hystrix. I understand when a service makes call to a 3rd party service and that service is not responding and threshold has been exceeded than the configuration, circuit will be opened and onward calls will be short circuited.
But I am not able to understand how circuit is closed again. Let us suppose our service is making call to 3rd party service and that service not not working fine so circuit is opened. After 5 minute that service has started working fine now circuit should be closed. How calling service knows this that the 3rd party service has started behaving fine, now circuited should be closed?
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In most situations, an open circuit is caused by a conductor breaking. The current cannot flow if the circuit is not closed and there is a break at any place in the loop. This results in an open circuit. Consider a bulb that is powered by a battery and controlled by a switch.
Spring Cloud's Circuit Breaker library provides an implementation of the Circuit Breaker pattern: when we wrap a method call in a circuit breaker, Spring Cloud Circuit Breaker watches for failing calls to that method, and if failures build up to a threshold, Spring Cloud Circuit Breaker opens the circuit so that ...
Half-Open: A limited number of requests from the application are allowed to pass through and invoke the operation. If these requests are successful, it's assumed that the fault that was previously causing the failure has been fixed and the circuit breaker switches to the Closed state (the failure counter is reset).
In order to implement Circuit Breaker in your application/microservice, you need to apply @EnableHystrix at the main class of your application. To see the analytics provided by Hystrix as a dashboard, apply @EnableHystrixDashboard at the main class.
There are actually three states: OPEN, CLOSED, and HALF_OPEN. Once the circuit breaker is OPEN and a certain amount of time has passed it lets a single request sneak through. This is the HALF_OPEN state. If successful the circuit breaker is closed, otherwise it returns to the OPEN state until that amount of time has passed again, where it enters the HALF_OPEN state once again. You can specify the amount of time between the transition to OPEN to HALF_OPEN using the circuitBreaker.sleepWindowInMilliseconds property.
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Consider the Hytrix circuit-breaker transition from CLOSED to OPEN. it short-circuits all requests made against that circuit-breaker.
After some amount of time (HystrixCommandProperties.circuitBreakerSleepWindowInMilliseconds()) the next single request is let through
(this is the HALF-OPEN state).
If the request fails, the circuit-breaker returns to the OPEN state for the duration of the sleep window. So, This HALF-OPEN state call determines whether to OPEN or CLOSE circuit.
If the request succeeds, the circuit-breaker transitions to CLOSED and the logic in 1. takes over again. checkout hystrix working.
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