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Azure Function for serving static files out of blob containers

Serve static files from all blob containers within a given storage account to clients over HTTP, respecting blobs' content types. Useful if you need to serve static files with App Service authentication.

How it works

A request for the URL /container/path will yield the path object in the blob container container. If path were a nested container with an index.html object within we'd redirect to /container/path/ and serve index.html. Note that all objects in all containers in the configured storage account will be accessible with no authorisation checks -- be sure that the data you're serving is intended to be public.

Why not use...

  • Static websites on Azure Storage? They don't provide for authentication, and doing "clever" routing via a VPN is too flakey.
  • Azure CDN? We want to ensure that users accessing these files are employed by us.

Requirements

  • A dedicated storage account. Don't share a storage account between the Function App and your data as Azure persists your secrets to the Function App storage and these will be accessible to clients via the Function.
  • If you're bringing your own domain, one of the D series plans. Consumption and shared plans don't allow for custom SSL bindings for your own certificates and will cause mismatched certificate common name errors. Microsoft ♥s Money.

Running it

  1. Create a new Azure Functions App using the .NET Core stack and Windows OS. The v3 host isn't yet available on Linux.
  2. Set the Runtime version of the app to ~3.
  3. Run func azure functionapp publish <FunctionAppName> from /AzureFunctionStaticFiles to build the app and publish it.
  4. Add the following Application settings:
    • AccountConnectionString must contain a connection string for your storage account.
    • IndexName sets the name of the default index page (Apache's DirectoryIndex, nginx's index).
    • HostName sets the name that should be used in redirects (optional; recommended if you're bringing your own domain or using a CDN).
  5. Configure a custom domain and SSL binding. Note that you'll need to bring your own certificate in PKCS12 (*.pfx) format. To ensure redirect paths are correct, alter HostName.
  6. Enable App Service Authentication with the Azure AD provider and make sure the default action for unauthenticated requests is to redirect users to it.

Hacking

Visual Studio

Grab a copy of Visual Studio 2019 and install the following workloads:

  • Azure development
  • .NET Core cross-platform development

Now continue on to the steps below.

Everyone

You'll need a local Node.js and Yarn installation to run the Azure Functions SDK. From the root of the repository, install the Azure Functions SDK:

yarn install

It's easiest to work with a local storage account running under the Azure Storage Emulator. Start the emulator by launching "Microsoft Azure Storage Emulator - v5.10" from the Start Menu. You can stop the emulator from the taskbar icon or by running the following in the resulting Command Prompt window:

.\AzureStorageEmulator.exe stop

You can then use the Azure SDK:

cd AzureFunctionStaticFiles/
yarn run func start

Testing

In Visual Studio

Open the Visual Studio Test Explorer and click Run.

From the console

dotnet test