Exercise - Add the coupon service


In this unit, you complete the Coupon.API project. You'll then run a script to generate changes to the WebSPA HTML, and generate and modify Helm charts to define the Kubernetes deployment.

Add the coupon service

You can find an ASP.NET Core project for the coupon service in the src/Services/Coupon/Coupon.API directory. Locate that directory in the explorer pane. Apply the following changes to the service:

  1. In Controllers/CouponController.cs, replace the comment // Add the GetCouponByCodeAsync method with the following code:

    public async Task<ActionResult<CouponDto>> GetCouponByCodeAsync(string code)
        var coupon = await _couponRepository.FindCouponByCodeAsync(code);
        if (coupon is null || coupon.Consumed)
            return NotFound();
        var couponDto = _mapper.Translate(coupon);
        return couponDto;

    In the preceding asynchronous action method:

    • The CouponRepository class' FindCouponByCodeAsync method retrieves the coupon corresponding to the provided code parameter value. The coupon is retrieved from a MongoDB database.
    • If the coupon returned is null or has already been used, an HTTP 404 status code is returned.
    • If the coupon returned isn't null and hasn't already been used, the Coupon object is converted to a CouponDto Data Transfer Object (DTO). Finally, an HTTP 200 status code is returned along with the DTO.
  2. Add real-time HTTP health checking to the coupon service by applying the following changes in Startup.cs:

    1. In the ConfigureServices method, invoke the custom AddCustomHealthCheck extension method immediately after the AddSwagger method call:

      public void ConfigureServices(IServiceCollection services)
          services.AddControllers(options => options.Filters.Add<ValidateModelAttribute>());
          services.AddTransient<IIntegrationEventHandler<OrderStatusChangedToAwaitingCouponValidationIntegrationEvent>, OrderStatusChangedToAwaitingCouponValidationIntegrationEventHandler>();
          services.AddTransient<IIntegrationEventHandler<OrderStatusChangedToCancelledIntegrationEvent>, OrderStatusChangedToCancelledIntegrationEventHandler>();

      With the preceding change:

      • ASP.NET Core's health check service is registered in the coupon service's dependency injection container. ASP.NET Core provides middleware that runs when you request a health check endpoint.

      • The AddCustomHealthCheck extension method (implemented in Extensions/IServiceCollectionExtensions.cs), tests external service dependencies to confirm availability and normal operation. An example of such an external dependency is MongoDB.

        public static IServiceCollection AddCustomHealthCheck(
          this IServiceCollection services,
          IConfiguration configuration)
            // code omitted for brevity
            var hcBuilder = services.AddHealthChecks();
            hcBuilder.AddCheck("self", () => HealthCheckResult.Healthy())
                    name: "CouponCollection-check",
                    tags: new string[] { "couponcollection" });

      The preceding code adds:

      • A health check named self, which returns an HTTP success status code for each request to the coupon service's health endpoint.
      • A check for its MongoDB dependency by using the AddMongoDb extension method. The AddMongoDb method is implemented in the AspNetCore.HealthChecks.MongoDb NuGet package.


      The open-source project AspNetCore.Diagnostics.HealthChecks provides various custom health check implementations for ASP.NET Core projects. The MongoDB implementation used in this step is just one example.

    2. In the Configure method, replace the // Add the endpoints.MapHealthChecks code comment with the highlighted code:

      public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
          if (env.IsDevelopment())
          var pathBase = Configuration["PATH_BASE"];
          if (!string.IsNullOrEmpty(pathBase))
              .UseSwaggerUI(options =>
                  options.SwaggerEndpoint($"{ (!string.IsNullOrEmpty(pathBase) ? pathBase : string.Empty) }/swagger/v1/swagger.json", "Coupon.API V1");
                  options.OAuthAppName("eShop-Learn.Coupon.API Swagger UI");
              .UseEndpoints(endpoints =>
                  endpoints.MapHealthChecks("/hc", new HealthCheckOptions
                      Predicate = _ => true,
                      ResponseWriter = UIResponseWriter.WriteHealthCheckUIResponse
                  endpoints.MapHealthChecks("/liveness", new HealthCheckOptions
                      Predicate = r => r.Name.Contains("self")

      The preceding change registers two HTTP health check endpoints with the ASP.NET Core routing system:

      • /liveness: A liveness endpoint that Kubernetes queries periodically to check for failures. Kubernetes provides liveness probes to detect applications that are failing, and restarts them when they don't return success codes. When the coupon service starts up for the first time, there might be time-consuming tasks, like setting up seed data in the database or awaiting RabbitMQ to start up. To avoid restarts during this time, the liveness check filters the checks with the self tag, which returns the HTTP status code 200 for every request.
      • /hc: A readiness endpoint that Kubernetes queries to know when a service is ready to start accepting traffic. It returns the HTTP status code 200 when all registered checks are successful. The same endpoint is also queried by an external health monitoring system, like the WebStatus app. WebStatus provides a dashboard to visualize configured health checks and the status of each. You use the AspNetCore.HealthChecks.UI.Client NuGet package to generate the dashboard.

      In the following Kubernetes deployment configuration file, the liveness and readiness probes use HTTP GET requests to the health endpoints mentioned previously, to determine their status codes. Any HTTP status code greater than or equal to 200, and less than 400, indicates success. Any other code indicates failure.

      kind: Deployment
      apiVersion: apps/v1
        name: coupon
          app: eshop
          service: coupon
        replicas: 1
            service: coupon
              app: eshop
              service: coupon
              - name: coupon-api
                image: {{ .Values.registry }}/coupon.api:linux-net6-initial
                imagePullPolicy: Always
                  - containerPort: 80
                    protocol: TCP
                  - containerPort: 81
                    protocol: TCP
                    port: 80
                    path: /liveness
                  initialDelaySeconds: 10
                  periodSeconds: 15
                    port: 80
                    path: /hc
                  initialDelaySeconds: 90
                  periodSeconds: 60
                  timeoutSeconds: 5
                  - configMapRef:
                      name: coupon-cm
  3. Save all your changes. In the terminal pane you created earlier, run the following command to build the coupon service project:

    dotnet build ../../src/Services/Coupon/Coupon.API/

    The build succeeds with no warnings. If the build fails, check the output for troubleshooting information.

  4. Open src/Services/Coupon/Coupon.API/Dockerfile. Notice the following things in this Dockerfile:

    • The ASP.NET Core runtime image is used as the base image of the multistage build.
    • The .NET SDK image is acquired to support the running of the following .NET Core CLI commands against the Coupon.API project:
      • dotnet restore: Restores the project's NuGet packages.
      • dotnet build: Builds the project in release mode. The build artifacts are written to the app/build/ directory of an intermediate image.
      • dotnet publish: Publishes the project in release mode. The published bundle is written to the app/publish/ directory of the final image.
    • The final image contains the ASP.NET Core runtime and the published coupon service artifacts.
    • When you start a container from the final image, you start the coupon service by running dotnet Coupon.API.dll.
  5. Run the following script in the terminal to make additional configuration changes for the coupon service:


    The preceding script:

    • Uncomments HTML markup in the WebSPA checkout and order details Angular components. This supports accepting coupon codes and displaying discount amounts, respectively. The following HTML markup in the Web/WebSPA/Client/src/modules/orders directory is uncommented:


      <div class="d-flex align-items-center justify-content-end mt-4 mb-4 text-uppercase">
          <div class="ml-3">${{order.subtotal | number:'.2-2'}}</div>
      <div class="d-flex align-items-center justify-content-end mt-4 mb-4 text-uppercase">
          <div class="ml-3">- ${{order.discount | number:'.2-2'}}</div>


      <div class="d-flex align-items-center justify-content-end mt-4 mb-4 text-uppercase">
          <div class="ml-3">${{order.total | number:'.2-2'}}</div>
      <div class="d-flex flex-nowrap justify-content-between align-items-center mb-3 mt-3">
              <div *ngIf="!coupon">
                  <div class="u-text-uppercase">Have a discount code?</div>
                  <div class="d-flex flex-nowrap justify-content-between align-items-center mt-1">
                      class="esh-orders_new-coupon mr-2 form-control"
                      placeholder="Coupon number"
                      (keydown)="keyDownValidationCoupon($event, discountcode.value)">
                          class="btn btn-secondary u-minwidth-unset">Apply</button>
                  <div class="mt-1" *ngIf="couponValidationMessage">{{couponValidationMessage}}</div>
          <div class="d-flex align-items-center justify-content-end text-uppercase">
              <div *ngIf="coupon?.code">{{coupon?.code}}</div>
                  <div class="text-right ml-3" *ngIf="coupon?.discount">-${{coupon?.discount | number:'.2-2'}}</div>
    • Creates a Helm chart for the coupon service in deploy/k8s/helm-simple/coupon.

    • Adds the coupon service endpoints to the aggregator Helm chart in deploy/k8s/helm-simple/webshoppingagg/templates/configmap.yaml.

    • Adds the coupon health check to the WebStatus Helm chart in deploy/k8s/helm-simple/webstatus/templates/configmap.yaml.

    To create an object in a Kubernetes cluster, you must provide the object specification in a YAML file. Helm's template functionality generates and sends the YAML to the cluster.

    The Helm chart for the coupon service is composed of the following files in the deploy/k8s/helm-simple/coupon directory:

    • Chart.yaml
    • templates/configmap.yaml
    • templates/deployment.yaml
    • templates/ingress.yaml
    • templates/service.yaml

    The Chart.yaml file contains a description of the chart. The templates directory contains template files. When Helm evaluates the chart with the helm install command, it sends all of the files in the templates directory to the template rendering engine. It then collects the rendered YAML created by those templates, and sends it to AKS.

Container images in Azure Container Registry

Host container images in container registries. Often, a public container registry like Docker Hub might be appropriate. Private container registries, such as Azure Container Registry, can be more appropriate for enterprise scenarios. Only your team and services have access to a private registry. All of the container images used when the solution was initially deployed to AKS are from one of the endpoints of Container Registry.

The following diagram depicts the relationships among Docker container images, container registries such as Container Registry, and Kubernetes or AKS deployments.

A container image is created by a developer, sent to Container Registry, and retrieved by AKS

In the preceding diagram:

  1. The developer sends the container image to Container Registry.
  2. The developer sends Kubernetes YAML configuration files to AKS. The configuration specifies which container images are required.
  3. AKS retrieves the images from Container Registry, and uses the images to build and run the containers.

You don't have permissions to make changes to the Container Registry of Microsoft. Consequently, you must host the coupon service container image and the modified WebSPA app container image on your private Container Registry.


The helm install command used later in the module specifies which container registry to use when you install the charts to Kubernetes or AKS.

Build the coupon service in Container Registry

Run the following script in the terminal. This builds the coupon service and WebSPA app container images, and hosts them in Container Registry:


The preceding script builds the container images in Container Registry by using the az acr build command, with the provided Dockerfile files for the Coupon.API and WebSPA projects.

Note that the solution isn't being built in your development container. The build occurs in the cloud when the container image is sent to Container Registry. You can see build output shown in the terminal. The az acr build command used by the script is shown in the terminal, with the correct parameters. The command resembles the following example (for reference only, do not run):

az acr build --registry eshoplearn \
     --image eshoplearn.azurecr.io/coupon.api:linux-net6-coupon \
     --file src/Services/Coupon/Coupon.API/Dockerfile \

In the preceding example:

  • The --registry parameter specifies the name of the container registry to use.
  • The --image parameter specifies the name and tag of the image, in the format <repo url>/<name>:<tag>.
  • The --file parameter specifies the relative path of Dockerfile.
  • The final parameter, which is positional and not indicated by a command-line flag, specifies the location of the local source code directory. In this case, the script uses the directory in which it's currently running, indicated by ..

In the next unit, you'll update the AKS deployment with your modifications.