Deploy Rust as an Azure Function

Continuous deployment to Azure Functions using Rust and GitHub Actions. This repository contains a sample Rust application that can be deployed to Azure Functions using GitHub Actions. Although not a requirement it is easier to use Visual Studio Code for development.

This repository is part of a Coursera MLOps course offered by Duke University

Prerequisites

This repository is also Codespaces ready, so you can use it directly from GitHub. The only requirement left would be to ensure you have an Azure account.

Use the following link as a reference to the Azure documentation

Running the application locally with Azure Functions Core Tools

Install the dependencies with cargo build
Start the Azure Functions Core Tools with func start (this feature is already installed with Codespaces)
Send a curl request to generate a JSON response

curl --header "Content-Type: application/json" \
  --request POST \
  --data '{"text":"example string"}' \
  http://localhost:7071/api/token

Creating the Azure Function in the Azure Portal

Use a unique name for the function app. This name will be used in the GitHub Actions workflow to deploy the application to Azure Functions. The name must be unique across all Azure Functions.

For the Runtime stack select Custom Handler and for the version select custom as well.

Select Linux as the Operating System and any region like East US.

Once the function app is created, click on Get Publish Profile and add it as a secret to the GitHub repository. The name of the secret should be AZURE_FUNCTIONAPP_PUBLISH_PROFILE and the value should be the content of the downloaded file.

Deploying with VSCode

Although you can deploy directlty from VSCode, you might encounter the following error when you try to re-deploy using a different method:

Error:   When request Azure resource at PublishContent, zipDepoy : WEBSITE_RUN_FROM_PACKAGE in your function app is set to an URL. Please remove WEBSITE_RUN_FROM_PACKAGE app setting from your function app.

This setting was created by the VSCode extension, so you must go to the portal, then to the function, next to Configuration, and then Application Settings, and delete WEBSITE_RUN_FROM_PACKAGE

Deploying with GitHub Actions

The workflow is defined in the .github/workflows/main.yml file. The workflow is set to be triggered manually via the workflow_dispatch setting. You can change this to trigger when a new commit is pushed to the main branch. The workflow will build the application and deploy it to Azure Functions.

The only requirement is to add the AZURE_CREDENTIALS secret to the repository. The value of the secret should be the output of the following command:

az ad sp create-for-rbac --name "rust-azure-function" --sdk-auth --role contributor --scopes /subscriptions/<SUBSCRIPTION_ID>/resourceGroups/<RESOURCE_GROUP_NAME>

The resulting output should look like:

  {
    "clientId": "<GUID>",
    "clientSecret": "<GUID>",
    "subscriptionId": "<GUID>",
    "tenantId": "<GUID>",
    (...)
  }

Copy those contents into the actions secrets as AZURE_CREDENTIALS. This secret is used in the workflow to authenticate with Azure.

Caveats

Currently, Rust is not a first class citizen in Azure Functions. This means that the deployment process is a bit more involved than other languages. If creating the function scaffolding in Visual Studio Code, you must select "custom" for the runtime, whereas other languages have their own category.

Deploying using the GitHub Actions for Functions does not work at the moment. The workflow will succeed but the function will timeout when invoked with an HTTP 500. The GitHub workflow uses instead the Azure Core Tools to deploy the function with the func command. This is a workaround until the GitHub Actions for Functions is fixed.