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Exposing ASP.NET Web API using .NET Core with Cloud Endpoints

Author(s): @simonz130 ,   Published: 2018-04-10

Simon Zeltser | Developer Programs Engineer | Google

Contributed by Google employees.

This tutorial shows how to create a simple API using ASP.NET Core Web API, deploy that API to the App Engine flexible environment, then use Cloud Endpoints to expose and monitor the API.

Step 1 - Set up your development environment

You will write code using Visual Studio Code. Therefore, you should install the following:

Step 2 - Create ASP.NET Core Web API using VS Code

  1. Open a command-line prompt and run the following commands:

    mkdir ExposeAPIWithEndpointsCore
    cd ExposeAPIWithEndpointsCore
    dotnet new webapi

    This will create a template Web API project using .NET Core 2.0.

  2. Open the ExposeAPIWithEndpointsCore folder you created in Visual Studio Code. It will look like this:

    VS Code First Screen

  3. Click on "YES" for "Required assets to build and debug are missing from ExposeAPIWithEndpointsCore. Add them?"

  4. Press F5 to build the template project.

  5. Navigate to http://localhost:5000/api/values in your browser.

    This is the output you should expect: [“value1”, “value2”].

    Now we have a pre-built "Values" controller in our sample project that exposes five HTTP REST APIs. Now we need to add OpenAPI support.

    OpenAPI is a set of specifications that describe REST APIs. It’s a format that is both machine and human readable. Originally this set of specifications was called Swagger but it was later renamed to OpenAPI. You can read more to understand the idea behind OpenAPI.

    We need it to deploy API specification to Cloud Endpoints later on. We have two options - either create OpenAPI specification manually, or use Swashbuckle tool that will auto-generate the specifications for us based on API definition. Of course, I prefer the second option. You will find it beneficial over time, as you make changes to the API. To add it, we need to add a few nuget packages: Swashbuckle.AspNetCore and Swagger and then configure Swagger in our service startup.

  6. In VS Code terminal, type this:

    dotnet add package Swashbuckle.AspNetCore
  7. Make changes in Startup.cs.

    1. In "using" section at the start of the document, add this:

      using Swashbuckle.AspNetCore.Swagger;
    2. In ConfigureServices method, add this:

      public void ConfigureServices(IServiceCollection services)
          // Register the Swagger generator
          services.AddSwaggerGen(c =>
                  new Info { Title = "My API", Version = "v1" });
    3. In "Configure" method, add this:

      public void Configure(
          IApplicationBuilder app,
          IHostingEnvironment env)
          if (env.IsDevelopment())
          // Enable middleware to serve generated Swagger as a JSON endpoint.
          // Enable middleware to serve swagger-ui (HTML, JS, CSS, etc.), specifying the Swagger JSON endpoint.
          app.UseSwaggerUI(c =>
              c.SwaggerEndpoint("/swagger/v1/swagger.json", "My API V1");

Step 3 - Create OpenAPI specification for our API

  1. Press F5 in VS Code. Browse to http://localhost:5000/swagger/v1/swagger.json

    You should see Open API specification for our APIs in JSON format. However we will work with YAML representation of the same JSON. Even though Google Endpoints supports both json and YAML representations of OpenAPI, YAML is much more human friendly, so in case we will want to make manual changes to the specification, doing it in YAML file will be easier.

  2. Copy the JSON content from the browser and paste it into https://editor.swagger.io. You will be asked whether to translate JSON to YAML. Say YES. You will see this:

    Swagger Editor

  3. Create a new file in VS Code under the main folder ExposeApiWithEndpointsCore. Name it openapi.yaml and paste the content of the generated YAML from https://editor.swagger.io.

    Now we are ready to deploy the API to Google Cloud!

Step 4 - Create a new Google Cloud project

  1. Create a new project at https://console.cloud.google.com

    We will create App Engine flexible environment and deploy our API to it from the command line. So now we need to make sure that the Cloud SDK is preconfigured to work with the project we just created.

  2. Open the Cloud SDK command line in elevated mode (Administrator), and type the following:

    1. Update SDK components to the latest

      gcloud components update
    2. Make sure that gcloud has permissions to work with our cloud project.

      gcloud auth login

      This will open a new browser window where you need to authenticate using your user account.

    3. Configure default project for all subsequent commands we will execute:

      gcloud config set project `YOUR_PROJECT_ID`
    4. Create App Engine flexible environment to which we will deploy our API. You can find the list of supported regions here.

      gcloud app create --project --region=`YOUR_REGION`

Now it's time to deploy the API specification and API implementation.

Step 5 - Deploy API specification to Cloud Endpoints

  1. Open openapi.yaml that was created in step 3.

  2. Add host declaration right before the paths section. The value should be YOUR-PROJECT-ID.appspot.com (replace YOUR-PROJECT-ID with your Cloud project ID):

    swagger: '2.0'
    version: v1
    title: My API
    host: YOUR-PROJECT-ID.appspot.com
        - Values
        operationId: ApiValuesGet

    When you will deploy API specification to Endpoints, it will create a new Cloud Endpoints service configuration with the name equals to host value from our OpenAPI yaml. Each endpoints deployment assigns a unique configuration_id for versioning purposes. When we will deploy the service implementation to App Engine flexible environment in the next step, it will create a DNS entry in the format of YOUR-PROJECT_ID.appspot.com. We should use that FQDN to make incoming requests to our API.

  3. In the Cloud SDK command prompt, make sure you are in the folder that contains openapi.yaml that was created in step 3. Execute:

    gcloud endpoints services deploy openapi.yaml

    You should notice that the deployment shows a few warnings, such as Operation does not require an API Key. You can ignore these for now.

    So what has happened now? You just deployed API specification. This created a new Cloud Endpoints service configuration entry with the name that we specified in “host” field of openapi.yaml. This service entry is preconfigured to serve the API based on the specifications in yaml file. Now we want to ensure that all incoming API calls will be intercepted by Cloud Endpoints and then routed for execution to the service we deploy to App Engine flexible environment.

Step 6 - Deploy API implementation to App Engine flexible environment

Now you need to deploy API implementation. You also need to bind API specification we deployed earlier to API implementation instance, so that every incoming request passes through Cloud Endpoints service first, before it hits the deployment of API implementation.

When deploying App Engine flexible service, you should specify Endpoints service name in the app.yaml. You should also set deployment rollout strategy to managed. By doing that, you instruct App Engine flexible environment to place an instance of Cloud Endpoints service in front of your API implementation. That instance is identified by service name and configuration id. By setting rollout_strategy=managed in app.yaml, we instruct the service to always use latest version of Cloud Endpoints service (the one that was deployed last).

  1. In the Cloud SDK shell type:

    gcloud endpoints configs list --service=`YOUR-PROJECT-ID`.appspot.com

    The output will show the CONFIG_ID and SERVICE_NAME.

  2. Create app.yaml file in VS Code at ExploreApiWithEndpointsCore directory. The content of the file should be:

    runtime: aspnetcore
    env: flex
        name: [SERVICE_NAME]
        rollout_strategy: managed

    Replace [SERVICE_NAME] with corresponding value of previous command output.

    By creating app.yaml with endpoints_api_service section, we effectively created the binding that will ensure that every incoming request to our API (specification is detailed in configuration with config_id) that will hit YOUR-PROJECT-ID.appspot.com (“name”), will be routed to our service.

    Now you are almost ready to deploy API implementation into AppEngine Flex. In order to separate a project from its publish package in dotnet core, you should deploy the outcome of dotnet publish command. That output by default doesn’t contain app.yaml file we created earlier.

  3. Edit “ExposeAPIWithEndpointsCore.csproj” in Visual Studio Code so that it always copies app.yaml into the publish directory by adding the content in this file to your ExposeAPIWithEndpointsCore.csproj file right before the closing Project tag.

  4. Deploy API implementation to the App Engine flexible environment.

    dotnet publish
    gcloud app deploy bin\debug\netcoreapp2.0\publish\app.yaml
  5. Test that your APIs are exposed properly. Open https://[YOUR-PROJECT-ID].appspot.com/api/Values in any browser. If you get ["value1","value2"] back, you are done!

Verifying the deployment

You now have the API deployed and exposed via Cloud Endpoints! To verify that, go to Endpoints page of Google Cloud Console. There you can inspect the requests graph, which should reflect the requests you make to test the API. You can also view all of the configurations of your endpoints deployments.

Monitoring API


You created a basic ASP.NET Core Web API, deployed it to App Engine flexible environment on Google Cloud and configured Cloud Endpoints in front of the API, so all the incoming requests will be sent to Cloud Endpoints which in turn will route them to API implementation. You haven’t implemented all the non functional requirements of exposing the API like security, throttling and monitoring yet. In this tutorial the API is exposed to everyone without any authentication.

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