Refactoring resilience implementation in order to use Polly directly when creating the resilience policies

Author: dsrodenas

src/BuildingBlocks/Resilience/Resilience.Http/Policies/CircuitBreakerPolicy.cs

@@ -1,5 +1,4 @@
-using Microsoft.eShopOnContainers.BuildingBlocks.Resilience.Http.Policies;
-using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Logging;
 using Newtonsoft.Json;
 using Polly;
 using Polly.Wrap;
@@ -23,84 +22,14 @@ public class ResilientHttpClient : IHttpClient
         private ILogger<ResilientHttpClient> _logger;
         public HttpClient Inst => _client;
 
-        public ResilientHttpClient(List<Policy> policies, ILogger<ResilientHttpClient> logger)
+        public ResilientHttpClient(Policy[] policies, ILogger<ResilientHttpClient> logger)
         {
             _client = new HttpClient();
             _logger = logger;
 
             // Add Policies to be applied
-            _policyWrapper = Policy.WrapAsync(policies.ToArray());
-        }
-
-        public ResilientHttpClient(List<ResiliencePolicy> policies, ILogger<ResilientHttpClient> logger)
-        {
-            _client = new HttpClient();
-            _logger = logger;
-
-            // Add Policies to be applied
-            _policyWrapper = Policy.WrapAsync(GeneratePolicies(policies));
-        }
-
-        private Policy[] GeneratePolicies(IList<ResiliencePolicy> policies)
-        {
-            var pollyPolicies = new List<Policy>();
-
-            foreach (var policy in policies)
-            {
-                switch (policy)
-                {
-                    case RetryPolicy retryPolicy:
-                        pollyPolicies.Add(
-                            CreateRetryPolicy(
-                                retryPolicy.Retries,
-                                retryPolicy.BackoffSeconds,
-                                retryPolicy.ExponentialBackoff));
-                        break;
-
-                    case CircuitBreakerPolicy circuitPolicy:
-                        pollyPolicies.Add(
-                            CreateCircuitBreakerPolicy(
-                                circuitPolicy.ExceptionsAllowedBeforeBreaking,
-                                circuitPolicy.DurationOfBreakInMinutes));
-                        break;
-                }
-            }
-
-            return pollyPolicies.ToArray();
-        }
-
-        private Policy CreateRetryPolicy(int retries, int backoffSeconds, bool exponentialBackoff) =>            
-            Policy.Handle<HttpRequestException>()
-                .WaitAndRetryAsync(
-                retries,               
-                retryAttempt => exponentialBackoff ? TimeSpan.FromSeconds(Math.Pow(backoffSeconds, retryAttempt)) : TimeSpan.FromSeconds(backoffSeconds),
-                (exception, timeSpan, retryCount, context) =>
-                {
-                    var msg = $"Retry {retryCount} implemented with Polly's RetryPolicy " +
-                        $"of {context.PolicyKey} " +
-                        $"at {context.ExecutionKey}, " +
-                        $"due to: {exception}.";
-                    _logger.LogWarning(msg);
-                    _logger.LogDebug(msg);
-                }
-            );
-
-        private Policy CreateCircuitBreakerPolicy(int exceptionsAllowedBeforeBreaking, int durationOfBreakInMinutes) =>
-           Policy.Handle<HttpRequestException>()
-           .CircuitBreakerAsync(
-               exceptionsAllowedBeforeBreaking,
-               TimeSpan.FromMinutes(durationOfBreakInMinutes),
-               (exception, duration) =>
-               {
-                   // on circuit opened
-                   _logger.LogTrace("Circuit breaker opened");
-               },
-               () =>
-               {
-                   // on circuit closed
-                   _logger.LogTrace("Circuit breaker reset");
-               }
-           );
+            _policyWrapper = Policy.WrapAsync(policies);
+        }        
 
         public Task<string> GetStringAsync(string uri) =>
             HttpInvoker(() => 

src/BuildingBlocks/Resilience/Resilience.Http/Policies/RetryPolicy.cs

@@ -0,0 +1,10 @@
+using Microsoft.eShopOnContainers.BuildingBlocks.Resilience.Http;
+using System;
+
+namespace Microsoft.eShopOnContainers.WebMVC.Infrastructure
+{
+    public interface IResilientHttpClientFactory
+    {
+        ResilientHttpClient CreateResilientHttpClient();
+    }
+}

src/BuildingBlocks/Resilience/Resilience.Http/ResiliencePolicyFactory.cs

@@ -0,0 +1,59 @@
+using Microsoft.eShopOnContainers.BuildingBlocks.Resilience.Http;
+using Microsoft.Extensions.Logging;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Polly;
+using System.Net.Http;
+
+namespace Microsoft.eShopOnContainers.WebMVC.Infrastructure
+{
+    public class ResilientHttpClientFactory : IResilientHttpClientFactory
+    {
+        private readonly ILogger<ResilientHttpClient> _logger;
+
+        public ResilientHttpClientFactory(ILogger<ResilientHttpClient> logger) 
+            =>_logger = logger;        
+
+        public  ResilientHttpClient CreateResilientHttpClient()        
+            => new ResilientHttpClient(CreatePolicies(), _logger);
+
+
+        private Policy[] CreatePolicies()
+            => new Policy[]
+            {
+                Policy.Handle<HttpRequestException>()                
+                .WaitAndRetryAsync(
+                    // number of retries
+                    6,
+                    // exponential backofff
+                    retryAttempt => TimeSpan.FromSeconds(Math.Pow(2, retryAttempt)),
+                    // on retry
+                    (exception, timeSpan, retryCount, context) =>
+                    {
+                        var msg = $"Retry {retryCount} implemented with Polly's RetryPolicy " +
+                            $"of {context.PolicyKey} " +
+                            $"at {context.ExecutionKey}, " +
+                            $"due to: {exception}.";
+                        _logger.LogWarning(msg);
+                        _logger.LogDebug(msg);
+                    }),
+                Policy.Handle<HttpRequestException>()
+               .CircuitBreakerAsync(
+                   // number of exceptions before breaking circuit
+                   5,
+                   // time circuit opened before retry
+                   TimeSpan.FromMinutes(1),
+                   (exception, duration) =>
+                   {
+                        // on circuit opened
+                        _logger.LogTrace("Circuit breaker opened");
+                   },
+                   () =>
+                   {
+                        // on circuit closed
+                        _logger.LogTrace("Circuit breaker reset");
+                   })};
+    }
+}

src/BuildingBlocks/Resilience/Resilience.Http/ResilientHttpClient.cs

@@ -16,6 +16,7 @@
 using Microsoft.Extensions.Options;
 using Microsoft.Extensions.HealthChecks;
 using Microsoft.eShopOnContainers.BuildingBlocks.Resilience.Http;
+using Microsoft.eShopOnContainers.WebMVC.Infrastructure;
 
 namespace Microsoft.eShopOnContainers.WebMVC
 {
@@ -63,19 +64,14 @@ public void ConfigureServices(IServiceCollection services)
 
             if (Configuration.GetValue<string>("UseResilientHttp") == bool.TrueString)
             {
-                services.AddSingleton(
-                    new List<ResiliencePolicy>
-                    {
-                        ResiliencePolicyFactory.CreateRetryPolicy(6, 2, true),
-                        ResiliencePolicyFactory.CreateCiscuitBreakerPolicy(5, 1)
-                    });
-                services.AddTransient<IHttpClient, ResilientHttpClient>();
+                services.AddTransient<IResilientHttpClientFactory, ResilientHttpClientFactory>();
+                services.AddTransient<IHttpClient, ResilientHttpClient>(sp => sp.GetService<IResilientHttpClientFactory>().CreateResilientHttpClient());
             }
             else
             {
                 services.AddTransient<IHttpClient, StandardHttpClient>();
             }
-        }
+        }        
 
         // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
         public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)