Ever had an ASP.NET Core application hit an external API, only for it to fail due to transient network issues or a temporary service overload? Manually implementing retry logic for every external call can quickly become tedious and error-prone, cluttering your business logic with cross-cutting concerns. This is where the Polly resilience library shines. Polly allows you to define sophisticated retry, circuit breaker, and other resilience policies in a declarative way, keeping your core application code clean and focused.
One of the most common and effective uses of Polly is for HTTP request retries within ASP.NET Core. By integrating Polly with HttpClientFactory, you can automatically apply a retry policy to all outgoing requests made by a specific HttpClient instance. This means that if an API call temporarily fails (e.g., with a 5xx status code or a HttpRequestException), Polly will automatically retry it based on the policy you’ve defined, without you having to write any extra try-catch blocks in your controllers or services.
Here’s a practical example of how to configure a simple retry policy for an HttpClient in your ASP.NET Core application’s Startup.cs (or Program.cs in .NET 6+). This policy will retry a failed request up to 3 times, with a logarithmic backoff strategy to avoid overwhelming the failing service.
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Polly;
using Polly.Extensions.Http;
using System;
using System.Net.Http;
public class Startup
{
public void ConfigureServices(IServiceCollection services)
{
services.AddHttpClient("MyApiClient")
.AddPolicyHandler(HttpPolicyExtensions
.HandleTransientHttpError()
.WaitAndRetryAsync(3, retryAttempt =>
TimeSpan.FromSeconds(Math.Pow(2, retryAttempt))
));
// Other services
}
}
Try it: Add the code snippet above to your Startup.cs (or Program.cs if using .NET 6+) and inject IHttpClientFactory into a service. Then, create a client named “MyApiClient” and make an outgoing HTTP request. If the target API experiences a transient failure, you’ll see Polly automatically attempt retries.
This approach significantly improves the robustness of your application by gracefully handling temporary external service disruptions. Instead of your users encountering immediate errors, they might experience a slight delay, but the operation will often succeed on a subsequent attempt. This leads to a much better user experience and reduces the operational burden of debugging transient connectivity issues.