Microservice Resiliency

https://github.com/jeffgbutler/microservice-workshop-java/

https://jeffgbutler.github.io/microservice-workshop-java/

What is Hystrix?

In December 2018, Netflix announced that Hystrix is entering maintenance mode
At the same time, Pivotal and Netflix announced recommended replacements
The new recommended circuit breaker implementation is https://github.com/resilience4j/resilience4j
See https://spring.io/blog/2018/12/12/spring-cloud-greenwich-rc1-available-now for details
Updates to this workshop coming soon! But the basic concepts remain the same.

The circuit breaker is a wrapper over a command
The wrapper watches for failures and will call a fallback method if there is a failure
Once failures reach a certain threshold, the circuit will be "opened"
When a circuit is opened, only the fallback method will be called
The circuit breaker will periodically try the true method and if the failure rate falls below the threshold, then the circuit will be "closed" and traffic will begin flowing to the true service
Closed == Good

Hystrix is available as a dependency in the Spring Initializr
Hystrix is integrated with Feign...
- Add the @EnableCircuitBreaker annotation to a configuration class
- Set the property feign.hystrix.enabled=true
- Add a fallback implementation class on the @FeignClient annotation

Hystrix will publish a stream of information about the state of the curcuits on the /actuator/hystrix.stream endpoint
This data stream is hard for a human to consume!
The Hystrix dashboard will consume the stream and present a friendly UI
Netflix has stated that the Hystrix dashboard has some security vulnerabilites and should not be exposed publicly
PCF implements a circuit breaker dashboard in the Spring Cloud Services tile