Http throttle defaulting (Azure#2113)

src/WebJobs.Script.WebHost/Configuration/HttpOptionsSetup.cs

@@ -0,0 +1,38 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the MIT License. See License.txt in the project root for license information.
+
+using Microsoft.Azure.WebJobs.Extensions.Http;
+using Microsoft.Extensions.Options;
+
+namespace Microsoft.Azure.WebJobs.Script.WebHost.Configuration
+{
+    public class HttpOptionsSetup : IConfigureOptions<HttpOptions>
+    {
+        internal const int DefaultMaxConcurrentRequests = 100;
+        internal const int DefaultMaxOutstandingRequests = 200;
+        private readonly IEnvironment _environment;
+
+        public HttpOptionsSetup(IEnvironment environment)
+        {
+            _environment = environment;
+        }
+
+        public void Configure(HttpOptions options)
+        {
+            if (_environment.IsDynamic())
+            {
+                // when running under dynamic, we choose some default
+                // throttle settings.
+                // these can be overridden by the user in host.json
+                if (_environment.IsAppServiceEnvironment())
+                {
+                    // dynamic throttles are based on sandbox counters
+                    // which only exist in AppService
+                    options.DynamicThrottlesEnabled = true;
+                }
+                options.MaxConcurrentRequests = DefaultMaxConcurrentRequests;
+                options.MaxOutstandingRequests = DefaultMaxOutstandingRequests;
+            }
+        }
+    }
+}

src/WebJobs.Script.WebHost/WebScriptHostBuilderExtension.cs

@@ -6,6 +6,7 @@
 using Microsoft.Azure.WebJobs.Host.Executors;
 using Microsoft.Azure.WebJobs.Host.Timers;
 using Microsoft.Azure.WebJobs.Script.Diagnostics;
+using Microsoft.Azure.WebJobs.Script.WebHost.Configuration;
 using Microsoft.Azure.WebJobs.Script.WebHost.DependencyInjection;
 using Microsoft.Azure.WebJobs.Script.WebHost.Diagnostics;
 using Microsoft.Extensions.DependencyInjection;
@@ -23,6 +24,12 @@ public static IHostBuilder AddWebScriptHost(this IHostBuilder builder, IServiceP
             ILoggerFactory configLoggerFactory = rootServiceProvider.GetService<ILoggerFactory>();
 
             builder.UseServiceProviderFactory(new JobHostScopedServiceProviderFactory(rootServiceProvider, rootScopeFactory))
+                .ConfigureServices(services =>
+                {
+                    // register default configuration
+                    // must happen before the script host is added below
+                    services.ConfigureOptions<HttpOptionsSetup>();
+                })
                 .AddScriptHost(webHostOptions, configLoggerFactory, webJobsBuilder =>
                 {
                     webJobsBuilder

test/WebJobs.Script.Tests/Configuration/HttpOptionsSetupTests.cs

@@ -0,0 +1,62 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the MIT License. See License.txt in the project root for license information.
+
+using System.Threading.Tasks.Dataflow;
+using Microsoft.Azure.WebJobs.Extensions.Http;
+using Microsoft.Azure.WebJobs.Script.WebHost.Configuration;
+using Moq;
+using Xunit;
+
+namespace Microsoft.Azure.WebJobs.Script.Tests.Configuration
+{
+    public class HttpOptionsSetupTests
+    {
+        [Fact]
+        public void Configure_Dynamic_AppService_Defaults()
+        {
+            var mockEnvironment = new Mock<IEnvironment>(MockBehavior.Strict);
+            mockEnvironment.Setup(p => p.GetEnvironmentVariable(EnvironmentSettingNames.AzureWebsiteInstanceId)).Returns("1234");
+            mockEnvironment.Setup(p => p.GetEnvironmentVariable(EnvironmentSettingNames.AzureWebsiteSku)).Returns(ScriptConstants.DynamicSku);
+
+            var setup = new HttpOptionsSetup(mockEnvironment.Object);
+            var options = new HttpOptions();
+            setup.Configure(options);
+
+            Assert.True(options.DynamicThrottlesEnabled);
+            Assert.Equal(HttpOptionsSetup.DefaultMaxConcurrentRequests, options.MaxConcurrentRequests);
+            Assert.Equal(HttpOptionsSetup.DefaultMaxOutstandingRequests, options.MaxOutstandingRequests);
+        }
+
+        [Fact]
+        public void Configure_Dynamic_NonAppService_Defaults()
+        {
+            var mockEnvironment = new Mock<IEnvironment>(MockBehavior.Strict);
+            mockEnvironment.Setup(p => p.GetEnvironmentVariable(EnvironmentSettingNames.AzureWebsiteInstanceId)).Returns((string)null);
+            mockEnvironment.Setup(p => p.GetEnvironmentVariable(EnvironmentSettingNames.AzureWebsiteSku)).Returns(ScriptConstants.DynamicSku);
+
+            var setup = new HttpOptionsSetup(mockEnvironment.Object);
+            var options = new HttpOptions();
+            setup.Configure(options);
+
+            Assert.False(options.DynamicThrottlesEnabled);
+            Assert.Equal(HttpOptionsSetup.DefaultMaxConcurrentRequests, options.MaxConcurrentRequests);
+            Assert.Equal(HttpOptionsSetup.DefaultMaxOutstandingRequests, options.MaxOutstandingRequests);
+        }
+
+        [Fact]
+        public void Configure_Dedicated_DoesNotDefault()
+        {
+            var mockEnvironment = new Mock<IEnvironment>(MockBehavior.Strict);
+            mockEnvironment.Setup(p => p.GetEnvironmentVariable(EnvironmentSettingNames.AzureWebsiteInstanceId)).Returns("1234");
+            mockEnvironment.Setup(p => p.GetEnvironmentVariable(EnvironmentSettingNames.AzureWebsiteSku)).Returns("Dedicated");
+
+            var setup = new HttpOptionsSetup(mockEnvironment.Object);
+            var options = new HttpOptions();
+            setup.Configure(options);
+
+            Assert.False(options.DynamicThrottlesEnabled);
+            Assert.Equal(DataflowBlockOptions.Unbounded, options.MaxConcurrentRequests);
+            Assert.Equal(DataflowBlockOptions.Unbounded, options.MaxOutstandingRequests);
+        }
+    }
+}