Enhancing Backend Service Reliability with API Management's Circuit Breaker Feature

In the dynamic world of API management, ensuring the reliability and stability of backend services is paramount. To address this, API Management introduces a new feature called the circuit breaker (preview) in API version 2023-03-01, aimed at protecting backend services from being overwhelmed by excessive requests.

The circuit breaker property, available in the backend resource, allows you to define rules that determine when the circuit breaker should trip. This includes criteria such as the number or percentage of failure conditions within a defined time interval, as well as a range of status codes that indicate failures.

When the circuit breaker trips, API Management immediately ceases sending requests to the backend service for a specified duration. Instead, it returns a 503 Service Unavailable response to clients. This pause in traffic allows the backend service to recover from the overload condition. Once the trip duration has elapsed, the circuit resets, and traffic resumes to the backend service.

It's important to note that the backend circuit breaker is designed to complement existing rate-limiting and concurrency-limiting policies, providing an additional layer of protection for both the API Management gateway and your backend services.

However, there are a few important considerations to keep in mind. Firstly, the backend circuit breaker is not currently supported in the Consumption tier of API Management. Additionally, due to the distributed nature of the API Management architecture, circuit breaker tripping rules are approximate. Different instances of the gateway do not synchronize, so each instance applies circuit breaker rules based on its own information.

To implement a circuit breaker in a backend, you can use the API Management REST API or tools like Bicep or ARM templates. For example, you can configure a circuit breaker in a backend named "myBackend" in your API Management instance "myAPIM" to trip when there are three or more 5xx status codes indicating server errors in a day, resetting after one hour.

In conclusion, the circuit breaker feature in API Management offers a powerful tool for enhancing the reliability and resilience of your backend services. By intelligently managing traffic flow during overload situations, the circuit breaker helps ensure a more stable and consistent API experience for your users.

Azure API Management backends | Microsoft Learn

Include a snippet similar to the following in your Bicep template for a backend resource with a circuit breaker:

resource symbolicname 'Microsoft.ApiManagement/service/backends@2023-03-01-preview' = {
  name: 'myAPIM/myBackend'
  properties: {
    url: 'https://mybackend.com'
    protocol: 'https'
    circuitBreaker: {
      rules: [
        {
          failureCondition: {
            count: 3
            errorReasons: [
              'Server errors'
            ]
            interval: 'P1D'
            statusCodeRanges: [
              {
                min: 500
                max: 599
              }
            ]
          }
          name: 'myBreakerRule'
          tripDuration: 'PT1H'
        }
      ]
    }
   }
 }