How can you use circuit breakers in microservices?

Microservices are a popular architectural style for building distributed systems that are composed of small, independent, and loosely coupled services. However, microservices also introduce new challenges, such as network latency, service failures, and cascading errors. How can you design your microservices to be resilient and fault-tolerant? One solution is to use the circuit breaker pattern, which is a design pattern that prevents a network or service failure from causing more failures and degrading the performance of the entire system. In this article, you will learn what the circuit breaker pattern is, how it works, and how you can implement it in your microservices.

1 What is the circuit breaker pattern?

The circuit breaker pattern is inspired by the electrical circuit breaker, which is a device that automatically interrupts the current flow when a fault is detected, such as a short circuit or an overload. The circuit breaker protects the electrical system from damage and allows the fault to be isolated and fixed. Similarly, the circuit breaker pattern is a software component that monitors the communication between a service and its dependencies, such as other services, databases, or external APIs. The circuit breaker detects failures and breaks the connection to the faulty dependency, preventing further requests from being sent and wasting resources. The circuit breaker also provides a fallback mechanism to handle the failure gracefully, such as returning a default value, a cached response, or an error message. The circuit breaker can also recover from the failure by periodically checking the status of the dependency and restoring the connection when it is available again.

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2 How does the circuit breaker work?

The circuit breaker works by switching between three states: closed, open, and half-open. In the closed state, the circuit breaker allows requests to pass through to the dependency normally. It also records the success and failure of each request and calculates the failure rate or the number of consecutive failures. If the failure rate or the number of consecutive failures exceeds a predefined threshold, the circuit breaker transitions to the open state. In the open state, the circuit breaker rejects all requests to the dependency and returns a fallback response. It also starts a timer to track the duration of the open state. When the timer expires, the circuit breaker transitions to the half-open state. In the half-open state, the circuit breaker allows a limited number of requests to pass through to the dependency and evaluates the outcome. If the requests are successful, the circuit breaker transitions back to the closed state. If the requests fail, the circuit breaker transitions back to the open state and resets the timer.

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3 How can you implement the circuit breaker in your microservices?

There are different ways to implement the circuit breaker in your microservices, depending on your programming language, framework, and tools. One option is to use a library or a framework that provides built-in support for the circuit breaker pattern, such as Hystrix for Java, Polly for .NET, or Resilience4j for Java 8. These libraries or frameworks allow you to configure and apply the circuit breaker to your service calls, as well as monitor and manage the circuit breaker metrics and events. Another option is to use a service mesh, such as Istio or Linkerd, that provides a layer of infrastructure between your microservices and handles the network communication, security, and reliability aspects. A service mesh can implement the circuit breaker pattern at the network level, without requiring any changes to your application code. You can define and apply the circuit breaker rules and policies to your service mesh configuration, as well as observe and control the circuit breaker behavior.

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Amritpal Singh

CTO at Zapbuild Technologies
In .NET, We generally use the package Polly for introducing the Retry or Circuit Breaker Policies. You can create a Policy and provide the details of how many attempts you want to make to a failed service before the Circuit Opens (to prevent further calls to that service) and for how long the Circuit should keep open (Timespan). Then using this Policy Object, you can call the service (API) to apply that policy. AsyncCircuitBreakerPolicy<T> CBPolicy = Policy.HandleResult<Type>(r => (predicate here)) .CircuitBreakerAsync(intRetryAttempts, Timespan) Predicate can be any condition that identifies failure like r => r.StatusCode>=500
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4 What are the benefits of using the circuit breaker in your microservices?

Using a circuit breaker in your microservices can bring you several advantages, such as improving the availability and performance of your system by preventing requests to unhealthy dependencies and reducing response time and resource consumption. It can also enhance the user experience and satisfaction by providing meaningful feedback and alternative actions in case of failure, rather than displaying errors or timeouts. Moreover, a circuit breaker can help prevent cascading failures and system overload by isolating the impact of a single service failure and containing it from affecting other services. Lastly, it facilitates the recovery and restoration of your system by allowing the faulty dependency to heal without being overwhelmed by requests.

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5 What are the challenges of using the circuit breaker in your microservices?

Using the circuit breaker in your microservices can also pose some challenges. You need to choose the right parameters and thresholds for your circuit breaker, such as the failure rate, consecutive failures, timeout duration, and requests in the half-open state. These parameters can affect the sensitivity and responsiveness of your circuit breaker, as well as the trade-off between availability and consistency. Testing and debugging your circuit breaker is essential, especially in complex environments with multiple services and dependencies. You may need to simulate different failure scenarios and verify how your circuit breaker reacts. Additionally, tools and techniques like logging, dashboards, and distributed tracing can be used to monitor and trace circuit breaker events and metrics. Finally, you should coordinate and communicate your circuit breaker strategy and configuration across teams to ensure consistency among implementations.

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