Retry and Circuit Breaker Policy example .Net 6 and Polly

In this example, we’ll implement the Wait and Retry and Circuit Breaker policy using .Net 6 Web API and Polly. For more details on what Circuit Breaker is, refer to the MSDN documentation.

Create a WebAPI with ValuesController in .Net 6 which will always return an Exception in the Get call.

using Microsoft.AspNetCore.Mvc;

namespace ExternalAPI.Controllers
{
    [ApiController]
    [Route("[controller]")]
    public class ValuesController : ControllerBase
    {

        private readonly ILogger<ValuesController> _logger;

        public ValuesController(ILogger<ValuesController> logger)
        {
            _logger = logger;
        }

        [HttpGet]
        public ActionResult<IEnumerable<string>> Get()
        {
            throw new Exception("Error");
        }

    }
}

Let’s call this ExternalAPI and running on https://localhost:7250/.

Create another .Net 6 WebAPI called CircuitBreaker.Demo and install Polly and Newtonsoft.json Nuget packages.

Configure Polly and HttpClient in Program.cs file as shown below:

using Polly;
using Polly.Extensions.Http;

var builder = WebApplication.CreateBuilder(args);
var httpRetryPolicy = Policy.HandleResult<HttpResponseMessage>(r => !r.IsSuccessStatusCode)
    
    .WaitAndRetryAsync(3, retryAttempt => TimeSpan.FromSeconds(retryAttempt));

// Add services to the container.

builder.Services.AddControllers();
// Learn more about configuring Swagger/OpenAPI at https://aka.ms/aspnetcore/swashbuckle
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();
builder.Services.AddHttpClient("errorApi", c => { c.BaseAddress = new Uri("https://localhost:7250"); });
builder.Services.AddSingleton<IAsyncPolicy<HttpResponseMessage>>(httpRetryPolicy);


var app = builder.Build();

// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI();
}

app.UseHttpsRedirection();

app.UseAuthorization();

app.MapControllers();

app.Run();

Now add the PollyController to call the ExternalAPI using the HttpClient:

using Microsoft.AspNetCore.Mvc;
using Newtonsoft.Json;
using Polly;

namespace CircuitBreaker.Demo.Controllers
{
    [ApiController]
    [Route("[controller]")]
    public class PollyController : ControllerBase
    {

        private readonly ILogger<PollyController> _logger;
        private readonly IHttpClientFactory _httpClientFactory;
        private readonly IAsyncPolicy<HttpResponseMessage> _policy;

        public PollyController(ILogger<PollyController> logger, IHttpClientFactory httpClientFactory, IAsyncPolicy<HttpResponseMessage> policy)
        {
            _logger = logger;
            _httpClientFactory = httpClientFactory;
            _policy = policy;
        }

        [HttpGet(Name = "GetApiResult")]
        public async Task<ActionResult<IEnumerable<string>>> Get()
        {
            var client = _httpClientFactory.CreateClient("errorApi");
            var response = await _policy.ExecuteAsync(() => client.GetAsync("values"));
            response.EnsureSuccessStatusCode();
            return JsonConvert.DeserializeObject<string[]>(await response.Content.ReadAsStringAsync());
        }

    }
}

When you run both the APIs, the call to External APIs is automatically made using Wait and Retry policy after every retryAttempt number of seconds 3 times. After that, the calls are stopped as the ExternalAPI keeps giving 500 error.

CircuitBreaker example:

Now change the Http Retry Policy line in the Program.cs file to:

var httpRetryPolicy = Policy.HandleResult<HttpResponseMessage>(r => !r.IsSuccessStatusCode)
    .CircuitBreakerAsync(2, TimeSpan.FromSeconds(30));

The above line will open the circuit and will start giving Circuit Open Exception after 2 attempts and keep the circuit Open for 30 seconds, which means you cannot make further calls to the API for that duration. The Exception will now be shown as below:

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