Pull docker images before running (#275)

* Pull docker images before running
- This step also validates that docker is installed before trying to pull and before running so that logic can be removed from the DockerRunner.
- Let the application exit if it tye run fails to start.

Fixes #222

src/Microsoft.Tye.Hosting/DockerImagePuller.cs

@@ -0,0 +1,91 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Microsoft.Extensions.Logging;
+using Microsoft.Tye.Hosting.Model;
+
+namespace Microsoft.Tye.Hosting
+{
+    public class DockerImagePuller : IApplicationProcessor
+    {
+        private readonly ILogger _logger;
+
+        public DockerImagePuller(ILogger logger)
+        {
+            _logger = logger;
+        }
+
+        public async Task StartAsync(Application application)
+        {
+            var images = new HashSet<string>();
+
+            foreach (var s in application.Services)
+            {
+                if (s.Value.Description.RunInfo is DockerRunInfo docker)
+                {
+                    images.Add(docker.Image);
+                }
+            }
+
+            // No images, no docker skip it.
+            if (images.Count == 0)
+            {
+                return;
+            }
+
+            if (!await DockerDetector.Instance.IsDockerInstalled.Value)
+            {
+                _logger.LogError("Unable to detect docker installation. Docker is not installed.");
+
+                throw new CommandException("Docker is not installed.");
+            }
+
+            if (!await DockerDetector.Instance.IsDockerConnectedToDaemon.Value)
+            {
+                _logger.LogError("Unable to connect to docker daemon. Docker is not running.");
+
+                throw new CommandException("Docker is not running.");
+            }
+
+            var tasks = new Task[images.Count];
+            var index = 0;
+            foreach (var image in images)
+            {
+                tasks[index++] = PullContainerAsync(image);
+            }
+
+            await Task.WhenAll(tasks);
+        }
+
+        private async Task PullContainerAsync(string image)
+        {
+            await Task.Yield();
+
+            var command = $"pull {image}";
+
+            _logger.LogInformation("Running docker command {command}", command);
+
+            var result = await ProcessUtil.RunAsync(
+                           "docker",
+                           command,
+                           outputDataReceived: data => _logger.LogInformation("{Image}: " + data, image),
+                           errorDataReceived: data => _logger.LogInformation("{Image}: " + data, image),
+                           throwOnError: false);
+
+            if (result.ExitCode != 0)
+            {
+                throw new CommandException("Docker pull command failed");
+            }
+        }
+
+        public Task StopAsync(Application application)
+        {
+            return Task.CompletedTask;
+        }
+    }
+}

src/Microsoft.Tye.Hosting/DockerRunner.cs

@@ -61,22 +61,6 @@ namespace Microsoft.Tye.Hosting
 
         private async Task StartContainerAsync(Application application, Service service, DockerRunInfo docker)
         {
-            if (!await DockerDetector.Instance.IsDockerInstalled.Value)
-            {
-                _logger.LogError("Unable to start docker container for service {ServiceName}, Docker is not installed.", service.Description.Name);
-
-                service.Logs.OnNext($"Unable to start docker container for service {service.Description.Name}, Docker is not installed.");
-                return;
-            }
-
-            if (!await DockerDetector.Instance.IsDockerConnectedToDaemon.Value)
-            {
-                _logger.LogError("Unable to start docker container for service {ServiceName}, Docker is not running.", service.Description.Name);
-
-                service.Logs.OnNext($"Unable to start docker container for service {service.Description.Name}, Docker is not running.");
-                return;
-            }
-
             var serviceDescription = service.Description;
             var environmentArguments = "";
             var volumes = "";

src/Microsoft.Tye.Hosting/TyeHost.cs

@@ -60,13 +60,18 @@ namespace Microsoft.Tye.Hosting
 
         public async Task RunAsync()
         {
-            await StartAsync();
-
-            var waitForStop = new TaskCompletionSource<object?>(TaskCreationOptions.RunContinuationsAsynchronously);
-            _lifetime?.ApplicationStopping.Register(obj => waitForStop.TrySetResult(null), null);
-            await waitForStop.Task;
+            try
+            {
+                await StartAsync();
 
-            await StopAsync();
+                var waitForStop = new TaskCompletionSource<object?>(TaskCreationOptions.RunContinuationsAsynchronously);
+                _lifetime?.ApplicationStopping.Register(obj => waitForStop.TrySetResult(null), null);
+                await waitForStop.Task;
+            }
+            finally
+            {
+                await StopAsync();
+            }
         }
 
         public async Task<WebApplication> StartAsync()
@@ -91,14 +96,7 @@ namespace Microsoft.Tye.Hosting
 
             _logger.LogInformation("Dashboard running on {Address}", app.Addresses.First());
 
-            try
-            {
-                await _processor.StartAsync(_application);
-            }
-            catch (Exception ex)
-            {
-                _logger.LogError(0, ex, "Failed to launch application");
-            }
+            await _processor.StartAsync(_application);
 
             return app;
         }
@@ -280,6 +278,7 @@ namespace Microsoft.Tye.Hosting
                 new PortAssigner(logger),
                 new ProxyService(logger),
                 new HttpProxyService(logger),
+                new DockerImagePuller(logger),
                 new DockerRunner(logger, replicaRegistry),
                 new ProcessRunner(logger, replicaRegistry, ProcessRunnerOptions.FromArgs(args, servicesToDebug))
             };