Round #857

Build a Polly v8 ResiliencePipeline that retries on transient HTTP errors three times with exponential backoff, then trips a circuit breaker after five consecutive failures.

Here's an example of how you can build a Polly v8 ResiliencePipeline in C# that retries on transient HTTP errors three times with exponential backoff, then trips a circuit breaker after five consecutive failures: ```csharp using Polly; using Polly.CircuitBreaker; using Polly.Retry; using System; using System.Net.Http; using System.Threading.Tasks; public class ResiliencePipeline { private readonly HttpClient _httpClient; public ResiliencePipeline(HttpClient httpClient) { _httpClient = httpClient; } public async Task<string> ExecuteResilientRequestAsync(string url) { // Define the retry policy with exponential backoff var retryPolicy = Policy.Handle<HttpRequestException>(ex => IsTransientHttpError(ex)) .OrResult<HttpResponseMessage>(response => IsTransientHttpError(response)) .WaitAndRetryAsync( retryCount: 3, retryAttempt => TimeSpan.FromSeconds(Math.Pow(2, retryAttempt)), (exception, timeSpan, retryCount, context) => { Console.WriteLine($"Retry {retryCount} after {timeSpan.TotalSeconds} seconds. Exception: {exception.Message}"); }); // Define the circuit breaker policy var circuitBreakerPolicy = Policy.Handle<HttpRequestException>(ex => IsTransientHttpError(ex)) .OrResult<HttpResponseMessage>(response => IsTransientHttpError(response)) .CircuitBreakerAsync( exceptionsAllowedBeforeBreaking: 5, durationOfBreak: TimeSpan.FromMinutes(1), onBreak: (exception, timeSpan, context) => { Console.WriteLine($"Circuit broken. Exception: {exception.Message}. Duration of break: {timeSpan.TotalMinutes} minutes"); }, onReset: (context) => { Console.WriteLine("Circuit reset"); }); // Combine the retry and circuit breaker policies var resiliencePipeline = Policy.WrapAsync(retryPolicy, circuitBreakerPolicy); // Execute the resilient request return await resiliencePipeline.ExecuteAsync(async () => { var response = await _httpClient.GetAsync(url); response.EnsureSuccessStatusCode(); return await response.Content.ReadAsStringAsync(); }); } private bool IsTransientHttpError(HttpRequestException ex) { // Check if the exception is a transient HTTP error if (ex.InnerException is SocketException socketException) { return socketException.SocketErrorCode == SocketError.ConnectionRefused || socketException.SocketErrorCode == SocketError.TimedOut || socketException.SocketErrorCode == SocketError.HostNotFound; } return false; } private bool IsTransientHttpError(HttpResponseMessage response) { // Check if the response is a transient HTTP error return response.StatusCode == System.Net.HttpStatusCode.GatewayTimeout || response.StatusCode == System.Net.HttpStatusCode.ServiceUnavailable || response.StatusCode == System.Net.HttpStatusCode.BadGateway; } } ``` In this example, the `ResiliencePipeline` class defines a pipeline that combines a retry policy with a circuit breaker policy. The retry policy retries on transient HTTP errors three times with exponential backoff, while the circuit breaker policy trips after five consecutive failures and remains broken for one minute. You can use the `ResiliencePipeline` class as follows: ```csharp var httpClient = new HttpClient(); var resiliencePipeline = new ResiliencePipeline(httpClient); var url = "https://example.com"; var response = await resiliencePipeline.ExecuteResilientRequestAsync(url); Console.WriteLine(response); ``` This code will execute a GET request to the specified URL with the resilience pipeline, retrying on transient HTTP errors and tripping the circuit breaker after five consecutive failures.

```csharp using Polly; using Polly.Extensions.Http; public class ResiliencePipelineBuilder { public static IAsyncPolicy<HttpResponseMessage> BuildResiliencePipeline() { var retryPolicy = Policy.Handle<HttpRequestException>(ex => ex.InnerException is SocketException) .OrResult<HttpResponseMessage>(r => r.StatusCode == HttpStatusCode.ServiceUnavailable) .WaitAndRetryAsync( retryCount: 3, retryAttempt => TimeSpan.FromSeconds(Math.Pow(2, retryAttempt)), (exception, span) => Console.WriteLine($"Retrying in {span.TotalSeconds} seconds...") ); var circuitBreakerPolicy = Policy.Handle<HttpRequestException>(ex => ex.InnerException is SocketException) .OrResult<HttpResponseMessage>(r => r.StatusCode == HttpStatusCode.ServiceUnavailable) .CircuitBreakerAsync( exceptionsAllowedBeforeBreaking: 5, durationOfBreak: TimeSpan.FromMinutes(1), onBreak: (ex, ts) => Console.WriteLine($"Circuit broken for {ts.TotalMinutes} minutes..."), onReset: () => Console.WriteLine("Circuit reset.") ); return Policy.WrapAsync(retryPolicy, circuitBreakerPolicy); } } ``` This implementation uses Polly's `Policy.Handle` to catch transient HTTP errors and `WaitAndRetryAsync` to implement exponential backoff. The `CircuitBreakerAsync` policy is used to trip the circuit after five consecutive failures. The `Policy.WrapAsync` method is used to combine the retry and circuit breaker policies into a single resilience pipeline.