In the microservices world, to fulfill a client request one microservice may need to talk to other microservices.
We should minimize this kind of direct dependencies on other microservices but in some cases it is unavoidable.
If a microservice is down or not functioning properly then the issue may cascade up to the upstream services.
Netflix created Hystrix library implementing Circuit Breaker pattern to address these kinds of issues.

Test

A practical guide to implementing the Circuit Breaker pattern in Spring Boot microservices using Netflix Hystrix via Spring Cloud. Covers adding the Hystrix dependency, enabling circuit breakers with @EnableCircuitBreaker, applying @HystrixCommand with fallback methods, configuring timeout and error threshold properties, handling ThreadLocal variable propagation across Hystrix threads using a custom HystrixConcurrencyStrategy, and monitoring circuit breaker status with the Hystrix Dashboard and Turbine.

MicroServices - Part 4 : Spring Cloud Circuit Breaker using Netflix Hystrix

Implementing Netflix Hystrix Circuit Breaker pattern

Monitoring Circuit Breakers using Hystrix Dashboard