Failures and circuit breakers

We have discussed most of the important concepts related to the microservices architecture. Such mechanisms, such as service discovery, API gateways, and configuration servers, are useful elements that help us to create a reliable and efficient system. Even if you have considered many aspects of these while designing your system's architecture, you should always be prepared for failures. In many cases, the reasons for failures are totally beyond the control of the holder, such as network or database problems. Such errors can be particularly severe for microservice-based systems, where one input request is processed in many subsequent calls. The first good practice is to always use network timeouts when waiting for a response. If a single service has a performance problem, we should try to minimize the impact on the rest. It is better to send an error response than to wait on a reply for a long time, blocking other threads. 

An interesting solution for the network timeout problems might be the circuit breaker pattern. It is a concept closely related to the microservice approach. A circuit breaker is responsible for counting successful and failed requests. If the error rate exceeds an assumed threshold, it trips and causes all further attempts to fail immediately. After a specific period of time, the API client should get back to sending requests, and if they succeed, it closes the circuit breaker. If there are many instances of each service available and one of them works slower than others, the result is that it is overlooked during the load balancing process. The second often-used mechanism for dealing with partial network failures is fallback. This is a logic that has to be performed when a request fails. For example, a service can return cached data, a default value, or an empty list of results. Personally, I'm not a big fan of this solution. I would prefer to propagate error code to other systems than return cached data or default values.