Circuit Breaker

The circuit breaker pattern is meant to enhance application resilience by preventing repeated attempts to perform operations that are likely to fail. Similar to an electrical circuit breaker, it monitors recent failures in a service or operation. If failures exceed a threshold within a defined window, the circuit breaker temporarily stops further attempts, allowing the service time to recover. This prevents cascading failures and conserves resources, improving application stability.

Wikipedia: Circuit breaker design pattern

Why

Stops sending requests to failing services, giving them time to recover and preventing overload.
Isolates issues in one service from affecting others, maintaining overall system stability.
Prevents unnecessary retries, saving bandwidth and reducing server load.

Overall, the circuit breaker pattern ensures more resilient and responsive interactions between clients and backend systems, leading to better performance and reliability.

State Diagaram

stateDiagram-v2
    [*] --> Closed
    Closed --> Closed : success
    Closed --> Opened : n failures\n within window x
    Opened --> HalfOpened : recovery time\n passed
    HalfOpened --> Closed : success
    HalfOpened --> Opened : failure

Usage

The following code demonstrates how to use a CircuitBreaker to execute asynchronous tasks, such as network requests:

let breaker = await CircuitBreaker(config: config)
let processedData = try await breaker.run {
    let (data, response) = try await URLSession.shared.data(from: url)
    // Handle the data and response
    return processedData
}

If the task fails and the circuit was closed, the CircuitBreaker will rethrow the original error from the task. If the circuit is open or half-open and the task fails, the CircuitBreaker will throw a CircuitOpenError. In all other cases the result of the task is returned.

Note:

If a CircuitOpenError is thrown, the operation should not be immediately repeated. The circuit breaker is open and will take time to recover. Any repeated tasks will have no effect during this recovery period.

Config

To configure the CircuitBreaker, you need to set its parameters based on your application's specific requirements:

name: Identifier for the service or task category (used for logging and monitoring).
group: Optional group name for debugging and categorization.
recoveryTimeout: Time to wait before moving from open to half-open state.
maxFailures: Maximum allowed failures within the rolling window to trip the breaker.
rollingWindow: Time period for counting failures to trigger the open state.

// Example configuration
let config = CircuitBreaker.Config(
    name: "UserServiceAPI",
    group: "NetworkServices",
    recoveryTimeout: 30, // 30 seconds
    maxFailures: 5, // Maximum 5 failures
    rollingWindow: 60 // Within a 60-second window
)

License

HL3 license promotes ethical software development by requiring adherence to guidelines that prevent harm and respect human rights and ensures the software is freely usable and modifiable.

CircuitBreaker

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