Uploading and CDN-preloading static content with Azure Functions

Overview

This sample demonstrates how Azure services can be used to upload static content and make it immediately available for fast downloads all over the world.

Using Azure For Content Uploads

This sample shows how to use Azure Functions to create a restful backend API for uploading content to Azure storage via a standard HTML form. After a completed upload, the new file is preloaded to Azure CDN for immediate local availability.

Building and setup

The steps below require Java 8 or later, Maven 3.3 or later, and either Azure CLI or PowerShell with the Az module. Azure CloudShell can be used if these dependencies are not available locally.

  1. Copy the file deployment.properties.template to deployment.properties and fill in the values. For example: ``` location=eastus

functionAppResourceGroup=contentUpload functionAppName=contentuploader

cdnSubscriptionId=00000000-0000-0000-0000-000000000000 cdnResourceGroup=contentUpload cdnProfileName=uploadcdnprofile cdnEndpointName=uploadendpoint

storageSubscriptionId=00000000-0000-0000-0000-000000000000 storageResourceGroup=contentUpload storageAccountName=uploadstorageaccount storageContainerName=uploads ```

  1. Run mvn package azure-functions:deploy. This will create the resource group specified by functionAppResourceGroup in step 1, and upload the Azure Functions application. It will also popul

  2. Provision the storage account for content and the CDN infrastructure by running one of the following:

    • setup.ps1 in PowerShell. This requires the Az PowerShell module, which can be install by running Install-Module Az. You must be logged into your azure account (via Connect-AzAccount) prior to running.
    • setup.sh in a *nix shell. This requires Azure CLI to be installed. You must be logged into your azure account (via az login) prior to running.

At the end of the script, a webpage will be generated (upload.html) through which you can test the file upload.

Note: when an Azure Endpoint is first provisioned using Verizon as the CDN provider, it may take about 90 minutes for the registration to complete.

Using the solution

Open upload.html, which will be generated by the setup script. This is a standard HTML form that, when submitted, will make a POST request containing the file content to the Azure Function.

Use the Network Inspector in your browser's web tools to observe that the function returns HTTP status code 200, indicating success.

Once the upload completes, you should see your file become available at the CDN endpoint. Its URL will be https://<endpoint name>.azureedge.net/<storage container name>/<file name>. If, when attempting to access that URL, you get a 404/Resource Not Found error, it likely means that the CDN registration has not been completed.

How it works

Accepting the upload

To accept a POST request with binary content, we a create a POJO with a public method annotated as follows:

@FunctionName("uploadFile")
public HttpResponseMessage run(@HttpTrigger(name = "requestTrigger",  methods = {
    HttpMethod.POST }, authLevel = AuthorizationLevel.ANONYMOUS) HttpRequestMessage<Optional<byte[]>> request,
    final ExecutionContext context) {
        ...
    }

This creates an HTTP endpoint that accepts a POST request at the URL https://<functionAppName>.azurewebsites.net/api/uploadFile. Note: uploadFile is the annotated FunctionName.

Using the Azure SDK from an Azure Function

We use the Azure SDK to perform the core workloud of the function: writing file contents to Azure Blob Storage, and preloading the newly written files to Azure CDN.

Credentials and Permissions

We use Azure Managed Identity to enable Azure Functions to inject credentials to access Azure. To use Azure Managed Identity, we first enable it from the setup scripts:

PowerShell: powershell Set-AzWebApp -AssignIdentity $true -Name $config.functionAppName -ResourceGroupName $config.functionAppResourceGroup Azure CLI: bash az webapp identity assign --name "$functionAppName" --resource-group "$functionAppResourceGroup"

This creates a Service Principal for the Functions application. In order to authorize the functions application to write to Azure Blob Storage and preload to Azure CDN, we assign this service principal a Contributor role on these resources:

PowerShell: powershell $appServicePrincipal = Get-AzADServicePrincipal -DisplayName $config.functionAppName New-AzRoleAssignment -Scope $storageAccount.Id -RoleDefinitionName Contributor -ApplicationId $appServicePrincipal.ApplicationId New-AzRoleAssignment -Scope $cdnProfile.Id -RoleDefinitionName Contributor -ApplicationId $appServicePrincipal.ApplicationId

Azure CLI: bash functionSpAppId=$(az ad sp list --display-name "$functionAppName" --query '[].appId' -otsv) az role assignment create --scope "$storageAccountId" --assignee "$functionSpAppId" --role Contributor az role assignment create --scope "$cdnProfileId" --assignee "$functionSpAppId" --role Contributor

With the requisite roles now granted to our Function Application's service principal, we can now create an authenticated Azure SDK client within our function's code:

Azure azure = Azure.authenticate(new AppServiceMSICredentials(AzureEnvironment.AZURE))
        .withSubscription(cdnSubscriptionId);

Configuration

We use App Settings of Azure Functions to inject identifying information of outside resources, such as the CDN profile and the Blob Storage container.

Because we use the Azure Functions Maven plugin to deploy the application, we use the same plugin to publish App Settings: xml <plugin> <groupId>com.microsoft.azure</groupId> <artifactId>azure-functions-maven-plugin</artifactId> <configuration> <resourceGroup>${functionAppResourceGroup}</resourceGroup> <appName>${functionAppName}</appName> <region>${location}</region> <appSettings> ... <property> <name>STORAGE_SUBSCRIPTION_ID</name> <value>${storageSubscriptionId}</value> </property> <property> <name>STORAGE_RESOURCE_GROUP</name> <value>${storageResourceGroup}</value> </property> <property> <name>STORAGE_ACCOUNT_NAME</name> <value>${storageAccountName}</value> </property> <property> <name>STORAGE_CONTAINER_NAME</name> <value>${storageContainerName}</value> </property> <property> <name>CDN_SUBSCRIPTION_ID</name> <value>${cdnSubscriptionId}</value> </property> <property> <name>CDN_RESOURCE_GROUP</name> <value>${cdnResourceGroup}</value> </property> <property> <name>CDN_PROFILE_NAME</name> <value>${cdnProfileName}</value> </property> <property> <name>CDN_ENDPOINT_NAME</name> <value>${cdnEndpointName}</value> </property> </appSettings> </configuration> <executions> <execution> <id>package-functions</id> <goals> <goal>package</goal> </goals> </execution> </executions> </plugin>

From inside the Azure function code, the values of App Settings can be read as environment variables: java String storageAccountSubscriptionId = System.getenv("STORAGE_SUBSCRIPTION_ID"); String storageAccountName = System.getenv("STORAGE_ACCOUNT_NAME"); String storageContainerName = System.getenv("STORAGE_CONTAINER_NAME"); String storageResourceGroup = System.getenv("STORAGE_RESOURCE_GROUP");

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