In modern software systems – especially those built with microservices or distributed architectures – applications often need to call external services (like other microservices, databases, or APIs). These remote calls come with the risk of failures or slow responses. If a service becomes unresponsive and the application keeps calling it, the results can be disastrous: requests pile up, threads hang, and eventually the failure cascades into a wider outage. The Circuit Breaker Pattern is a design pattern that addresses this problem by improving system resilience and fault tolerance. Just like an electrical circuit breaker trips to prevent damage when there’s an overload, a software circuit breaker “trips” to stop calls to a failing service. This allows the system to fail fast and recover gracefully instead of grinding to a halt. Popularized by Michael Nygard in his book Release It!, the Circuit Breaker Pattern has become an essential tool in modern software engineering to build robust, reliable applications.

Example in Microservices

Imagine a microservice for processing customer orders. This service (Order Service) communicates with a Payment Service to process payments. If the Payment Service starts to fail or become slow, the Order Service will continue to make calls, waiting and potentially failing itself.

With a circuit breaker implemented:

• After noticing a set number of failed attempts to the Payment Service, the circuit breaker trips.
• The Order Service stops calling the Payment Service, returning a default response like "Payment processing is delayed" or it might queue the order for later processing.
• After a cooldown period, the circuit breaker allows a few requests to check if the Payment Service is back to normal.