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--- title: Create serverless APIs using Azure Functions and API Management description: Use Visual Studio to create an HTTP triggered function that uses an OpenAPI definition (formerly swagger) to expose a serverless API using API Management. ms.topic: tutorial ms.date: 08/04/2024 --- # Create serverless APIs in Visual Studio using Azure Functions and API Management integration REST APIs are often described using an OpenAPI definition (formerly known as Swagger) file. This file contains information about operations in an API and how the request and response data for the API should be structured. In this tutorial, you learn how to: > [!div class="checklist"] > * Create the code project in Visual Studio > * Install the OpenAPI extension > * Add an HTTP trigger endpoint, which includes OpenAPI definitions > * Test function APIs locally using built-in OpenAPI functionality > * Publish project to a function app in Azure > * Enable API Management integration > * Download the OpenAPI definition file The serverless function you create provides an API that lets you determine whether an emergency repair on a wind turbine is cost-effective. Since you create both the function app and API Management instance in a consumption tier, your cost for completing this tutorial is minimal. ## Prerequisites + [Visual Studio 2022](https://azure.microsoft.com/downloads/). Make sure you select the **Azure development** workload during installation. + An active [Azure subscription](../guides/developer/azure-developer-guide.md#understanding-accounts-subscriptions-and-billing), create a [free account](https://azure.microsoft.com/pricing/purchase-options/azure-account?cid=msft_learn) before you begin. ## Create the code project The Azure Functions project template in Visual Studio creates a project that you can publish to a function app in Azure. You'll also create an HTTP triggered function from a template that supports OpenAPI definition file (formerly Swagger file) generation. 1. From the Visual Studio menu, select **File** > **New** > **Project**. 1. In **Create a new project**, enter *functions* in the search box, choose the **Azure Functions** template, and then select **Next**. 1. In **Configure your new project**, enter a **Project name** for your project like `TurbineRepair`, and then select **Create**. 1. For the **Create a new Azure Functions application** settings, select one of these options for **Functions worker**, where the option you choose depends on your chosen process model: ### [Isolated worker model](#tab/isolated-process) **.NET 8.0 Isolated (Long Term Support)**: Your C# functions run in the isolated worker model, which is recommended. For more information, see the [isolated worker model guide](dotnet-isolated-process-guide.md). ### [In-process](#tab/in-process) [!INCLUDE [functions-in-process-model-retirement-note](../../includes/functions-in-process-model-retirement-note.md)] **.NET 8.0 (Long Term Support)**: Your C# functions run in the [in-process model](functions-dotnet-class-library.md), which will be retired. To learn more, see the [in-process model guide](functions-dotnet-class-library.md). --- 1. For the rest of the options, use the values in the following table: | Setting | Value | Description | | ------------ | ------- |----------------------------------------- | | **Function template** | **Empty** | This creates a project without a trigger, which gives you more control over the name of the HTTP triggered function when you add it later. | | **Use Azurite for runtime storage account (AzureWebJobsStorage)** | **Selected** | You can use the emulator for local development of HTTP trigger functions. Because a function app in Azure requires a storage account, one is assigned or created when you publish your project to Azure. | | **Authorization level** | **Function** | When running in Azure, clients must provide a key when accessing the endpoint. For more information, see [Authorization level](functions-bindings-http-webhook-trigger.md#http-auth). | 1. Select **Create** to create the function project. Next, you update the project by installing the OpenAPI extension for Azure Functions, which enables the discoverability of API endpoints in your app. ## Install the OpenAPI extension To install the OpenAPI extension: 1. From the **Tools** menu, select **NuGet Package Manager** > **Package Manager Console**. 1. In the console, run the following [Install-Package](/nuget/tools/ps-ref-install-package) command to install the OpenAPI extension: ### [Isolated worker model](#tab/isolated-process) ```command NuGet\Install-Package Microsoft.Azure.Functions.Worker.Extensions.OpenApi -Version 1.5.1 ``` You might need to update the [specific version](https://www.nuget.org/packages/Microsoft.Azure.Functions.Worker.Extensions.OpenApi), based on your version of .NET. ### [In-process model](#tab/in-process) ```command NuGet\Install-Package Microsoft.Azure.WebJobs.Extensions.OpenApi -Version 1.5.1 ``` You might need to update the [specific version](https://www.nuget.org/packages/Microsoft.Azure.WebJobs.Extensions.OpenApi), based on your version of .NET. --- Now, you can add your HTTP endpoint function. ## Add an HTTP endpoint function In a C# class library, the bindings used by the function are defined by applying attributes in the code. To create a function with an HTTP trigger: 1. In **Solution Explorer**, right-click your project node and select **Add** > **New Azure Function**. 1. Enter **Turbine.cs** for the class, and then select **Add**. 1. Choose the **Http trigger** template, set **Authorization level** to **Function**, and then select **Add**. A Turbine.cs code file is added to your project that defines a new function endpoint with an HTTP trigger. Now you can replace the HTTP trigger template code with code that implements the Turbine function endpoint, along with attributes that use OpenAPI to define endpoint. ## Update the function code The function uses an HTTP trigger that takes two parameters: | Parameter name | Description| | ---- | ---- | | *hours* | The estimated time to make a turbine repair, up to the nearest whole hour. | | *capacity* | The capacity of the turbine, in kilowatts. | The function then calculates how much a repair costs, and how much revenue the turbine could make in a 24-hour period. Parameters are supplied either in the query string or in the payload of a POST request. In the Turbine.cs project file, replace the contents of the class generated from the HTTP trigger template with the following code, which depends on your process model: ### [Isolated worker model](#tab/isolated-process) :::code language="csharp" source="~/functions-openapi-turbine-repair-isolated/TurbineRepair/Turbine.cs"::: ### [In-process model](#tab/in-process) :::code language="csharp" source="~/functions-openapi-turbine-repair/TurbineRepair/Turbine.cs"::: --- This function code returns a message of `Yes` or `No` to indicate whether an emergency repair is cost-effective. It also returns the revenue opportunity that the turbine represents and the cost to fix the turbine. ## Run and verify the API locally When you run the function, the OpenAPI endpoints make it easy to try out the function locally using a generated page. You don't need to provide function access keys when running locally. 1. Press F5 to start the project. When Functions runtime starts locally, a set of OpenAPI and Swagger endpoints are shown in the output, along with the function endpoint. 1. In your browser, open the RenderSwaggerUI endpoint, which should look like `http://localhost:7071/api/swagger/ui`. A page is rendered, based on your OpenAPI definitions. 1. Select **POST** > **Try it out**, enter values for `hours` and `capacity` either as query parameters or in the JSON request body, and select **Execute**. :::image type="content" source="media/openapi-apim-integrate-vs/swagger-ui-post.png" alt-text="Swagger UI for testing the TurbineRepair API"::: 1. When you enter integer values like 6 for `hours` and 2500 for `capacity`, you get a JSON response that looks like the following example: :::image type="content" source="media/openapi-apim-integrate-vs/swagger-ui-response.png" alt-text="Response JSON data from the TurbineRepair function."::: Now you have a function that determines the cost-effectiveness of emergency repairs. Next, you publish your project and API definitions to Azure. ## Publish the project to Azure Before you can publish your project, you must have a function app in your Azure subscription. Visual Studio publishing creates a function app the first time you publish your project. It can also create an API Management instance that integrates with your function app to expose the TurbineRepair API. 1. In **Solution Explorer**, right-click the project and select **Publish** and in **Target**, select **Azure** then **Next**. 1. For the **Specific target**, choose **Azure Function App (Windows)** to create a function app that runs on Windows, then select **Next**. 1. In **Function Instance**, choose **+ Create a new Azure Function...**. :::image type="content" source="media/openapi-apim-integrate-vs/publish-new-resource.png" alt-text="Create a new function app instance"::: 1. Create a new instance using the values specified in the following table: | Setting | Value | Description | | ------------ | ------- | -------------------------------------------------- | | **Name** | Globally unique name | Name that uniquely identifies your new function app. Accept this name or enter a new name. Valid characters are: `a-z`, `0-9`, and `-`. | | **Subscription** | Your subscription | The Azure subscription to use. Accept this subscription or select a new one from the drop-down list. | | **[Resource group](../azure-resource-manager/management/overview.md)** | Name of your resource group | The resource group in which to create your function app. Select an existing resource group from the drop-down list or choose **New** to create a new resource group.| | **[Plan Type](functions-scale.md)** | Consumption | When you publish your project to a function app that runs in a [Consumption plan](consumption-plan.md), you pay only for executions of your functions app. Other hosting plans incur higher costs. | | **Location** | Location of the service | Choose a **Location** in a [region](https://azure.microsoft.com/regions/) near you or other services your functions access. | | **[Azure Storage](storage-considerations.md)** | General-purpose storage account | An Azure Storage account is required by the Functions runtime. Select **New** to configure a general-purpose storage account. You can also choose an existing account that meets the [storage account requirements](storage-considerations.md#storage-account-requirements). | :::image type="content" source="media/openapi-apim-integrate-vs/create-function-app-with-storage.png" alt-text="Create a new function app in Azure with Storage"::: 1. Select **Create** to create a function app and its related resources in Azure. Status of resource creation is shown in the lower left of the window. 1. Back in **Functions instance**, make sure that **Run from package file** is checked. Your function app is deployed using [Zip Deploy](functions-deployment-technologies.md#zip-deploy) with [Run-From-Package](run-functions-from-deployment-package.md) mode enabled. This deployment method is recommended for your functions project, since it results in better performance. 1. Select **Next**, and in **API Management** page, also choose **+ Create an API Management API**. 1. Create an **API in API Management** by using values in the following table: | Setting | Value | Description | | ------------ | ------- | -------------------------------------------------- | | **API name** | TurbineRepair | Name for the API. | | **Subscription name** | Your subscription | The Azure subscription to use. Accept this subscription or select a new one from the drop-down list. | | **Resource group** | Name of your resource group | Select the same resource group as your function app from the drop-down list. | | **API Management service** | New instance | Select **New** to create a new API Management instance in the same location in the serverless tier. Select **OK** to create the instance. | :::image type="content" source="media/openapi-apim-integrate-vs/create-api-management-api.png" alt-text="Create API Management instance with API"::: 1. Select **Create** to create the API Management instance with the TurbineRepair API from the function integration. 1. Select **Finish** and after the publish profile creation process completes, select **Close**. 1. Verify the Publish page now says **Ready to publish**, and then select **Publish** to deploy the package containing your project files to your new function app in Azure. After the deployment completes, the root URL of the function app in Azure is shown in the **Publish** tab. ## Get the function access key 1. In the **Publish** tab, select the ellipses (**...**) next to **Hosting** and select **Open in Azure portal**. The function app you created is opened in the Azure portal in your default browser. 1. Under **Functions** on the **Overview page**, select > **Turbine** then select **Function keys**. :::image type="content" source="media/openapi-apim-integrate-vs/get-function-keys.png" alt-text="Get an access key for the TurbineRepair function"::: 1. Under **Function keys**, select the *copy to clipboard* icon next to the **default** key. You can now set this key you copied in API Management so that it can access the function endpoint. ## Configure API Management 1. In the function app page, expand **API** and select **API Management**. 1. If the function app isn't already connected to the new API Management instance, select it under **API Management**, select **API** > **OpenAPI Document on Azure Functions**, make sure **Import functions** is checked, and select **Link API**. Make sure that only **TurbineRepair** is selected for import and then **Select**. 1. Select **Go to API Management** at the top of the page, and in the API Management instance, expand **APIs**. 1. Under **APIs** > **All APIs**, select **OpenAPI Document on Azure Functions** > **POST Run**, then under **Inbound processing** select **Add policy** > **Set query parameters**. 1. Below **Inbound processing**, in **Set query parameters**, type `code` for **Name**, select **+Value**, paste in the copied function key, and select **Save**. API Management includes the function key when it passes calls through to the function endpoint. :::image type="content" source="media/openapi-apim-integrate-vs/inbound-processing-rule.png" alt-text="Provide Function credentials to the API inbound processing rule"::: Now that the function key is set, you can call the `turbine` API endpoint to verify that it works when hosted in Azure. ## Verify the API in Azure 1. In the API, select the **Test** tab and then **POST Run**, enter the following code in the **Request body** > **Raw**, and select **Send**: ```json { "hours": "6", "capacity": "2500" } ``` :::image type="content" source="media/openapi-apim-integrate-vs/api-management-test-function-api.png" alt-text="OpenAPI test page in the API Management API"::: As before, you can also provide the same values as query parameters. 1. Select **Send**, and then view the **HTTP response** to verify the same results are returned from the API. ## Download the OpenAPI definition If your API works as expected, you can download the OpenAPI definition for the new hosted APIs from API Management. 1. 1. Under **APIs**, select **OpenAPI Document on Azure Functions**, select the ellipses (**...**), and select **Export**.  2. Choose the means of API export, including OpenAPI files in various formats. You can also [export APIs from Azure API Management to the Power Platform](../api-management/export-api-power-platform.md). ## Clean up resources In the preceding steps, you created Azure resources in a resource group. If you don't expect to need these resources in the future, you can delete them by deleting the resource group. From the Azure portal menu or **Home** page, select **Resource groups**. Then, on the **Resource groups** page, select the group you created. On the **myResourceGroup** page, make sure that the listed resources are the ones you want to delete. Select **Delete resource group**, type the name of your group in the text box to confirm, and then select **Delete**. ## Next steps You've used Visual Studio 2022 to create a function that's self-documenting because of the [OpenAPI Extension](https://github.com/Azure/azure-functions-openapi-extension) and integrated with API Management. You can now refine the definition in API Management in the portal. You can also [learn more about API Management](../api-management/api-management-key-concepts.md). > [!div class="nextstepaction"] > [Edit the OpenAPI definition in API Management](../api-management/edit-api.md)