Preparing the app

1. In your terminal window, clone the sample app repository to your local machine:

   gitclonehttps://github.com/GoogleCloudPlatform/getting-started-dotnet.git

   Alternatively, you can download the sample as a zip file and extract it.

2. Change to the directory that contains the background task sample code:

   cdgetting-started-dotnet/BackgroundProcessing

Understanding theTranslateWorker service

• The service starts by importing several dependencies likeFirestore and Translation.

  usingGoogle.Cloud.Firestore;usingGoogle.Cloud.Translation.V2;

• The Firestore and Translation clients areinitialized so they can be reused between handler invocations. That way, youdon't have to initialize new clients for every invocation, whichwould slow down execution.

  publicvoidConfigureServices(IServiceCollectionservices){services.AddSingleton<FirestoreDb>(provider=>FirestoreDb.Create(GetFirestoreProjectId()));services.AddSingleton<TranslationClient>(TranslationClient.Create());services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);}

• The Translation API translates the string to thelanguage you selected.

  varresult=await_translator.TranslateTextAsync(sourceText,"es");

• The controller's constructor receives the Firestore andPub/Sub clients.

  ThePost method parses the Pub/Submessage to get the text to translate. It uses the message ID as a unique namefor the translation request to make sure itdoesn't store any duplicate translations.

  usingGoogle.Cloud.Firestore;usingGoogle.Cloud.Translation.V2;usingMicrosoft.AspNetCore.Mvc;usingMicrosoft.Extensions.Logging;usingSystem;usingSystem.Collections.Generic;usingSystem.Text;usingSystem.Threading.Tasks;namespaceTranslateWorker.Controllers{/// <summary>/// The message Pubsub posts to our controller./// </summary>publicclassPostMessage{publicPubsubMessagemessage{get;set;}publicstringsubscription{get;set;}}/// <summary>/// Pubsub's inner message./// </summary>publicclassPubsubMessage{publicstringdata{get;set;}publicstringmessageId{get;set;}publicDictionary<string,string>attributes{get;set;}}[Route("api/[controller]")][ApiController]publicclassTranslateController:ControllerBase{privatereadonlyILogger<TranslateController>_logger;privatereadonlyFirestoreDb_firestore;privatereadonlyTranslationClient_translator;// The Firestore collection where we store translations.privatereadonlyCollectionReference_translations;publicTranslateController(ILogger<TranslateController>logger,FirestoreDbfirestore,TranslationClienttranslator){_logger=logger??thrownewArgumentNullException(nameof(logger));_firestore=firestore??thrownewArgumentNullException(nameof(firestore));_translator=translator??thrownewArgumentNullException(nameof(translator));_translations=_firestore.Collection("Translations");}/// <summary>/// Handle a posted message from Pubsub./// </summary>/// <param name="request">The message Pubsub posts to this process.</param>/// <returns>NoContent on success.</returns>[HttpPost]publicasyncTask<IActionResult>Post([FromBody]PostMessagerequest){// Unpack the message from Pubsub.stringsourceText;try{byte[]data=Convert.FromBase64String(request.message.data);sourceText=Encoding.UTF8.GetString(data);}catch(Exceptione){_logger.LogError(1,e,"Bad request");returnBadRequest();}// Translate the source text._logger.LogDebug(2,"Translating {0} to Spanish.",sourceText);varresult=await_translator.TranslateTextAsync(sourceText,"es");// Store the result in Firestore.Translationtranslation=newTranslation(){TimeStamp=DateTime.UtcNow,SourceText=sourceText,TranslatedText=result.TranslatedText};_logger.LogDebug(3,"Saving translation {0} to {1}.",translation.TranslatedText,_translations.Path);await_translations.Document(request.message.messageId).SetAsync(translation);// Return a success code.returnNoContent();}/// <summary>/// Serve a root page so Cloud Run knows this process is healthy./// </summary>[Route("/")]publicIActionResultIndex(){returnContent("Serving translate requests...");}}}

Deploying theTranslateWorker service

• In theBackgroundProcessing directory, run the PowerShell script to buildand deploy the service to Cloud Run:

  PublishTo-CloudRun.ps1

Understanding thePublishTo-CloudRun.ps1 script

ThePublishTo-CloudRun.ps1 script publishes the service to Cloud Run, andprotects the TranslateWorker service from being abused. If the service permitted allincoming connections, then anyone could post translate requests to the controllerand thereby incur costs. Therefore, you set up the service to only acceptPOST requests from Pub/Sub.

The script does the following:

1. Builds the app locally usingdotnet publish.
2. Builds a container that runs the app usingCloud Build.
3. Deploys the app to Cloud Run.
4. Enables the project to create Pub/Sub authentication tokens.
5. Creates a service account to represent the Pub/Sub subscription identity.
6. Gives the service account permission to invokeTranslateWorker service.

7. Creates a Pub/Sub topic and subscription.

   # 1. Build the application locally.dotnet publish -c Release# Collect some details about the project that we'll need later.$projectId = gcloud config get-value project$projectNumber = gcloud projects describe $projectId --format="get(projectNumber)"$region = "us-central1"# 2. Use Google Cloud Build to build the worker's container and publish to Google# Container Registry.gcloud builds submit --tag gcr.io/$projectId/translate-worker `    TranslateWorker/bin/Release/netcoreapp2.1/publish# 3. Run the container with Google Cloud Run.gcloud beta run deploy translate-worker --region $region --platform managed `    --image gcr.io/$projectId/translate-worker --no-allow-unauthenticated$url = gcloud beta run services describe translate-worker --platform managed `    --region $region --format="get(status.address.hostname)"# 4. Enable the project to create pubsub authentication tokens.gcloud projects add-iam-policy-binding $projectId `     --member=serviceAccount:service-$projectNumber@gcp-sa-pubsub.iam.gserviceaccount.com `     --role=roles/iam.serviceAccountTokenCreator# 5. Create a service account to represent the Cloud Pub/Sub subscription identity.$serviceAccountExists = gcloud iam service-accounts describe `    cloud-run-pubsub-invoker@$projectId.iam.gserviceaccount.com 2> $nullif (-not $serviceAccountExists) {    gcloud iam service-accounts create cloud-run-pubsub-invoker `        --display-name "Cloud Run Pub/Sub Invoker"}# 6. For Cloud Run, give this service account permission to invoke # translate-worker service.gcloud beta run services add-iam-policy-binding translate-worker `     --member=serviceAccount:cloud-run-pubsub-invoker@$projectId.iam.gserviceaccount.com `     --role=roles/run.invoker --region=$region# 7. Create a pubsub topic and subscription, if they don't already exist.$topicExists = gcloud pubsub topics describe translate-requests 2> $null if (-not $topicExists) {    gcloud pubsub topics create translate-requests}$subscriptionExists = gcloud pubsub subscriptions describe translate-requests 2> $nullif ($subscriptionExists) {    gcloud beta pubsub subscriptions modify-push-config translate-requests `        --push-endpoint $url/api/translate `        --push-auth-service-account cloud-run-pubsub-invoker@$projectId.iam.gserviceaccount.com} else {    gcloud beta pubsub subscriptions create translate-requests `        --topic translate-requests --push-endpoint $url/api/translate `        --push-auth-service-account cloud-run-pubsub-invoker@$projectId.iam.gserviceaccount.com}

Understanding theTranslateUI service

TheTranslateUI service renders a web page that displays recent translations,and accepts requests for new translations.

• TheStartUp class configures an ASP.NET app and createsPub/Sub and Firestore clients.

  usingGoogle.Apis.Auth.OAuth2;usingGoogle.Cloud.Firestore;usingGoogle.Cloud.PubSub.V1;usingMicrosoft.AspNetCore.Builder;usingMicrosoft.AspNetCore.Hosting;usingMicrosoft.AspNetCore.Mvc;usingMicrosoft.Extensions.Configuration;usingMicrosoft.Extensions.DependencyInjection;usingSystem;usingSystem.Net.Http;namespaceTranslateUI{publicclassStartup{publicStartup(IConfigurationconfiguration){Configuration=configuration;}publicIConfigurationConfiguration{get;}// This method gets called by the runtime. Use this method to add services to the container.publicvoidConfigureServices(IServiceCollectionservices){services.AddSingleton<FirestoreDb>(provider=>FirestoreDb.Create(GetFirestoreProjectId()));services.AddSingleton<PublisherClient>(provider=>PublisherClient.CreateAsync(newTopicName(GetProjectId(),GetTopicName())).Result);services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);}// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.publicvoidConfigure(IApplicationBuilderapp,IHostingEnvironmentenv){if(env.IsDevelopment()){app.UseDeveloperExceptionPage();}else{app.UseExceptionHandler("/Home/Error");// The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.app.UseHsts();}app.UseHttpsRedirection();app.UseStaticFiles();app.UseCookiePolicy();app.UseMvc(routes=>{routes.MapRoute(name:"default",template:"{controller=Home}/{action=Index}/{id?}");});}}}

• The index handlerIndex gets all existing translations fromFirestore and fills aViewModel with the list:

  usingGoogle.Cloud.Firestore;usingGoogle.Cloud.PubSub.V1;usingGoogle.Protobuf;usingMicrosoft.AspNetCore.Mvc;usingSystem.Diagnostics;usingSystem.Linq;usingSystem.Threading.Tasks;usingTranslateUI.Models;namespaceTranslateUI.Controllers{publicclassHomeController:Controller{privatereadonlyFirestoreDb_firestore;privatereadonlyPublisherClient_publisher;privateCollectionReference_translations;publicHomeController(FirestoreDbfirestore,PublisherClientpublisher){_firestore=firestore;_publisher=publisher;_translations=_firestore.Collection("Translations");}[HttpPost][HttpGet]publicasyncTask<IActionResult>Index(stringSourceText){// Look up the most recent 20 translations.varquery=_translations.OrderByDescending("TimeStamp").Limit(20);varsnapshotTask=query.GetSnapshotAsync();if(!string.IsNullOrWhiteSpace(SourceText)){// Submit a new translation request.await_publisher.PublishAsync(newPubsubMessage(){Data=ByteString.CopyFromUtf8(SourceText)});}// Render the page.varmodel=newHomeViewModel(){Translations=(awaitsnapshotTask).Documents.Select(doc=>doc.ConvertTo<Translation>()).ToList(),SourceText=SourceText};returnView(model);}[ResponseCache(Duration = 0, Location = ResponseCacheLocation.None, NoStore = true)]publicIActionResultError(){returnView(newErrorViewModel{RequestId=Activity.Current?.Id??HttpContext.TraceIdentifier});}}}

• New translations are requested by submitting an HTML form. The requesttranslation handler validates the request, and publishes amessage to Pub/Sub:

  // Submit a new translation request.await_publisher.PublishAsync(newPubsubMessage(){Data=ByteString.CopyFromUtf8(SourceText)});

Deploying theTranslateUI service

• In theBackgroundProcessing directory, run the PowerShell script to buildand deploy the service to Cloud Run:

  ./PublishTo-CloudRun.ps1

Understanding thePublishTo-CloudRun.ps1 script

ThePublishTo-CloudRun.ps1 script publishes the app to Cloud Run.

The script does the following:

1. Builds the app locally usingdotnet publish.
2. Builds a container that runs the app by usingCloud Build.

3. Deploys the app to Cloud Run.

   # 1. Build the application locally.dotnet publish -c Release# 2. Use Google Cloud Build to build the UI's container and publish to Google# Container Registry. gcloud builds submit --tag gcr.io/$projectId/translate-ui `    TranslateUI/bin/Release/netcoreapp2.1/publish# 3. Run the container with Google Cloud Run.gcloud beta run deploy translate-ui --region $region --platform managed `    --image gcr.io/$projectId/translate-ui --allow-unauthenticated

Testing the app

After successfully running thePublishTo-CloudRun.ps1 script, tryrequesting a translation.

1. The final command in thePublishTo-CloudRun.ps1 script tells you the URL for yourUI service. In your terminal window, find the URL for theTranslateUI service:

   gcloudbetarunservicesdescribetranslate-ui--region$region--format="get(status.address.hostname)"

2. In your browser, go to the URL that you got from the previous step.

   There is a page with an empty list of translations and a form to requestnew translations.

3. In theText to translate field, enter some text to translate, forexample,Hello, World.

4. ClickSubmit.

5. To refresh the page, clickRefreshrefresh. There is a newrow in the translation list. If you don't see a translation, wait a few moreseconds and try again. If you still don't see a translation, see thenext section about debugging the app.

Debugging the app

If you cannot connect to your Cloud Run service or don't see newtranslations, check the following:

• Check that thePublishTo-CloudRun.ps1 script successfully completed and didn'toutput any errors. If there were errors (for example,message=Build failed), fix them, and try running again.

• Check for errors in the logs:

  1. In the Google Cloud console, go to the Cloud Run page.

     Go to Cloud Run page

  2. Click the service name,translate-ui.

  3. ClickLogs.