split out readyness and live checks

Author: thefringeninja

src/SqlStreamStore.Server/HealthProbeMiddleware.cs

@@ -0,0 +1,41 @@
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Routing;
+using MidFunc = System.Func<
+    Microsoft.AspNetCore.Http.HttpContext,
+    System.Func<System.Threading.Tasks.Task>,
+    System.Threading.Tasks.Task
+>;
+
+namespace SqlStreamStore.Server
+{
+    internal static class HealthProbeMiddleware
+    {
+        public static IApplicationBuilder UseHealthProbe(
+            this IApplicationBuilder builder, IReadonlyStreamStore streamStore)
+            => builder.UseRouter(router => router
+                .MapMiddlewareGet("ready", inner => inner.Use(Ready(streamStore)))
+                .MapMiddlewareGet("live", inner => inner.Use(Live)));
+
+        private static MidFunc Live => (context, next) =>
+        {
+            context.Response.StatusCode = 204;
+            return Task.CompletedTask;
+        };
+
+        private static MidFunc Ready(IReadonlyStreamStore streamStore) => async (context, next) =>
+        {
+            try
+            {
+                await streamStore.ReadHeadPosition(context.RequestAborted);
+            }
+            catch
+            {
+                context.Response.StatusCode = 503;
+                return;
+            }
+
+            context.Response.StatusCode = 204;
+        };
+    }
+}

src/SqlStreamStore.Server/SqlStreamStoreServerStartup.cs

@@ -6,15 +6,14 @@
 using Microsoft.Extensions.DependencyInjection;
 using SqlStreamStore.HAL;
 using SqlStreamStore.Server.Browser;
+using MidFunc = System.Func<
+    Microsoft.AspNetCore.Http.HttpContext,
+    System.Func<System.Threading.Tasks.Task>,
+    System.Threading.Tasks.Task
+>;
 
 namespace SqlStreamStore.Server
 {
-    using MidFunc = System.Func<
-        Microsoft.AspNetCore.Http.HttpContext,
-        System.Func<System.Threading.Tasks.Task>,
-        System.Threading.Tasks.Task
-    >;
-
     internal class SqlStreamStoreServerStartup : IStartup
     {
         private readonly IStreamStore _streamStore;
@@ -29,11 +28,12 @@ public SqlStreamStoreServerStartup(
         }
 
         public IServiceProvider ConfigureServices(IServiceCollection services) => services
-            .AddResponseCompression(options => options.MimeTypes = new[] { "application/hal+json" })
+            .AddResponseCompression(options => options.MimeTypes = new[] {"application/hal+json"})
             .AddRouting()
             .BuildServiceProvider();
 
         public void Configure(IApplicationBuilder app) => app
+            .Map("/health", inner => inner.UseHealthProbe(_streamStore))
             .UseResponseCompression()
             .Use(VaryAccept)
             .UseSqlStreamStoreBrowser()

tests/SqlStreamStore.Server.Tests/SqlStreamStoreServerStartupTests.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Net;
 using System.Net.Http;
 using System.Net.Http.Headers;
 using System.Threading.Tasks;
@@ -39,14 +40,35 @@ public SqlStreamStoreServerStartupTests()
         [Fact]
         public async Task StartsUp()
         {
-            using (await _httpClient.SendAsync(new HttpRequestMessage(HttpMethod.Get, "/")
+            using (var response = await _httpClient.SendAsync(new HttpRequestMessage(HttpMethod.Get, "/")
             {
                 Headers = {Accept = {new MediaTypeWithQualityHeaderValue("application/hal+json")}}
             }))
             {
+                Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+            }
+
+            using (var response = await _httpClient.SendAsync(new HttpRequestMessage(HttpMethod.Get, "/health/ready")))
+            {
+                Assert.Equal(HttpStatusCode.NoContent, response.StatusCode);
+            }
+
+            using (var response = await _httpClient.SendAsync(new HttpRequestMessage(HttpMethod.Get, "/health/live")))
+            {
+                Assert.Equal(HttpStatusCode.NoContent, response.StatusCode);
             }
         }
 
+        [Fact]
+        public async Task ServiceUnavailableWhenNotReady()
+        {
+            _streamStore.Dispose();
+            using (var response = await _httpClient.SendAsync(new HttpRequestMessage(HttpMethod.Get, "/health/ready")))
+            {
+                Assert.Equal(HttpStatusCode.ServiceUnavailable, response.StatusCode);
+            }
+        }        
+
         public void Dispose()
         {
             _streamStore?.Dispose();