Polly CircuitBreaker, Retry and Timeout configuration example for HttpClient and HttpClientFactory

TestCircuitBreaker.Controllers.HomeController.cs

using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Logging;
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Net.Http;
using System.Threading.Tasks;
using TestCircuitBreaker.Models;

namespace TestCircuitBreaker.Controllers
{
	public class HomeController : Controller
	{
		private readonly ILogger<HomeController> _logger;
		private readonly IHttpClientFactory _factory;

		public HomeController(ILogger<HomeController> logger, IHttpClientFactory factory)
		{
			_logger = logger;
			_factory = factory;
		}

		public async Task<IActionResult> Index()
		{
			var client = _factory.CreateClient("localhost509");
			string result = await client.GetStringAsync("/");

			return Content(result);
		}

		public IActionResult Privacy()
		{
			return View();
		}

		[ResponseCache(Duration = 0, Location = ResponseCacheLocation.None, NoStore = true)]
		public IActionResult Error()
		{
			return View(new ErrorViewModel { RequestId = Activity.Current?.Id ?? HttpContext.TraceIdentifier });
		}
	}
}

TestCircuitBreaker.Startup.cs

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.HttpsPolicy;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Polly;
using Polly.Extensions.Http;
using Polly.Timeout;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Net.Http;
using System.Threading.Tasks;

// dotnet add package Polly.Extensions.Http
// dotnet add package Microsoft.Extensions.Http.Polly
// see: https://github.com/App-vNext/Polly/wiki/Polly-and-HttpClientFactory
namespace TestCircuitBreaker
{
	public class Startup
	{
		public Startup(IConfiguration configuration)
		{
			Configuration = configuration;
		}

		public IConfiguration Configuration { get; }

		// This method gets called by the runtime. Use this method to add services to the container.
		public void ConfigureServices(IServiceCollection services)
		{
			services.AddLogging();

			var retryPolicy = HttpPolicyExtensions
							  .HandleTransientHttpError()
							  .Or<TimeoutRejectedException>() // thrown by Polly's TimeoutPolicy if the inner execution times out
							  .RetryAsync(15);

			var timeoutPolicy = Policy.TimeoutAsync<HttpResponseMessage>(1);

			var circuitPolicy = HttpPolicyExtensions
							  .HandleTransientHttpError()
							  .Or<TimeoutRejectedException>()
							  .CircuitBreakerAsync(
								handledEventsAllowedBeforeBreaking: 5,
								durationOfBreak: TimeSpan.FromSeconds(20),
								onBreak: (response, timeSpan) =>
								{
									Console.Write("broken");
								},
								onReset: () =>
								{
									Console.WriteLine("reset");
								});

      // Retry executes Circuit (if the circuit is open, it fails), which executes Timeout
			services
				.AddHttpClient("localhost509", c => c.BaseAddress = new Uri("http://localhost:509"))
				.AddPolicyHandler(retryPolicy)
				.AddPolicyHandler(circuitPolicy)
				.AddPolicyHandler(timeoutPolicy);

			services.AddControllersWithViews();
		}

		// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
		public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
		{
			app.UseHttpsRedirection();
			app.UseStaticFiles();
			app.UseMiddleware<ExceptionMiddleware>();

			app.UseRouting();

			app.UseAuthorization();

			app.UseEndpoints(endpoints =>
			{
				endpoints.MapControllerRoute(
					name: "default",
					pattern: "{controller=Home}/{action=Index}/{id?}");
			});
		}
	}

	public class ExceptionMiddleware
	{
		private readonly RequestDelegate _next;

		public ExceptionMiddleware(RequestDelegate next)
		{
			_next = next;
		}

		public async Task Invoke(HttpContext httpContext)
		{
			try
			{
				await _next(httpContext);
			}
			catch (Exception ex)
			{
				Console.WriteLine($"================ {ex.GetType().ToString()}");
				httpContext.Response.StatusCode = StatusCodes.Status226IMUsed; // something to distinguish this middleware
				await httpContext.Response.WriteAsJsonAsync("{ 'a' : 1 }");
			}
		}
	}
}