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Create your first durable function in Azure using Python
Create and publish an Azure Durable Function in Python using Visual Studio Code.
anthonychu
quickstart
12/23/2020
azfuncdf, antchu
python
mode-api

Create your first durable function in Python

Durable Functions is an extension of Azure Functions that lets you write stateful functions in a serverless environment. The extension manages state, checkpoints, and restarts for you.

In this article, you learn how to use the Visual Studio Code Azure Functions extension to locally create and test a "hello world" durable function. This function will orchestrate and chain together calls to other functions. You then publish the function code to Azure.

Running durable function in Azure

Prerequisites

To complete this tutorial:

[!INCLUDE quickstarts-free-trial-note]

Create your local project

In this section, you use Visual Studio Code to create a local Azure Functions project.

  1. In Visual Studio Code, press F1 (or Ctrl/Cmd+Shift+P) to open the command palette. In the command palette, search for and select Azure Functions: Create New Project....

    Create function

  2. Choose an empty folder location for your project and choose Select.

  3. Following the prompts, provide the following information:

    Prompt Value Description
    Select a language for your function app project Python Create a local Python Functions project.
    Select a version Azure Functions v3 You only see this option when the Core Tools aren't already installed. In this case, Core Tools are installed the first time you run the app.
    Python version Python 3.6, 3.7, or 3.8 VS Code will create a virtual environment with the version you select.
    Select a template for your project's first function Skip for now
    Select how you would like to open your project Open in current window Reopens VS Code in the folder you selected.

Visual Studio Code installs the Azure Functions Core Tools, if needed. It also creates a function app project in a folder. This project contains the host.json and local.settings.json configuration files.

A requirements.txt file is also created in the root folder. It specifies the Python packages needed to run your function app.

Install azure-functions-durable from PyPI

When you created the project, the Azure Functions VS Code extension automatically created a virtual environment with your selected Python version. You will activate the virtual environment in a terminal and install some dependencies required by Azure Functions and Durable Functions.

  1. Open requirements.txt in the editor and change its content to the following:

    azure-functions
azure-functions-durable

  2. Open the editor's integrated terminal in the current folder (Ctrl+Shift+`).

  3. In the integrated terminal, activate the virtual environment in the current folder:

    Linux or macOS

    source .venv/bin/activate

    Windows

    .venv\scripts\activate

    Activate virtual environment

  4. In the integrated terminal where the virtual environment is activated, use pip to install the packages you just defined:

    python -m pip install -r requirements.txt

Create your functions

A basic Durable Functions app contains three functions:

  • Orchestrator function - describes a workflow that orchestrates other functions.
  • Activity function - called by the orchestrator function, performs work, and optionally returns a value.
  • Client function - a regular Azure Function that starts an orchestrator function. This example uses an HTTP triggered function.

Orchestrator function

You use a template to create the durable function code in your project.

  1. In the command palette, search for and select Azure Functions: Create Function....

  2. Following the prompts, provide the following information:

    Prompt Value Description
    Select a template for your function Durable Functions orchestrator Create a Durable Functions orchestration
    Provide a function name HelloOrchestrator Name of your durable function

You've added an orchestrator to coordinate activity functions. Open HelloOrchestrator/__init__.py to see the orchestrator function. Each call to context.call_activity invokes an activity function named Hello.

Next, you'll add the referenced Hello activity function.

Activity function

  1. In the command palette, search for and select Azure Functions: Create Function....

  2. Following the prompts, provide the following information:

    Prompt Value Description
    Select a template for your function Durable Functions activity Create an activity function
    Provide a function name Hello Name of your activity function

You've added the Hello activity function that is invoked by the orchestrator. Open Hello/__init__.py to see that it takes a name as input and returns a greeting. An activity function is where you'll perform actions such as making a database call or performing a computation.

Finally, you'll add an HTTP triggered function that starts the orchestration.

Client function (HTTP starter)

  1. In the command palette, search for and select Azure Functions: Create Function....

  2. Following the prompts, provide the following information:

    Prompt Value Description
    Select a template for your function Durable Functions HTTP starter Create an HTTP starter function
    Provide a function name DurableFunctionsHttpStart Name of your client function
    Authorization level Anonymous For demo purposes, allow the function to be called without authentication

You've added an HTTP triggered function that starts an orchestration. Open DurableFunctionsHttpStart/__init__.py to see that it uses client.start_new to start a new orchestration. Then it uses client.create_check_status_response to return an HTTP response containing URLs that can be used to monitor and manage the new orchestration.

You now have a Durable Functions app that can be run locally and deployed to Azure.

Test the function locally

Azure Functions Core Tools lets you run an Azure Functions project on your local development computer. If you don't have it installed, you're prompted to install these tools the first time you start a function from Visual Studio Code.

  1. To test your function, set a breakpoint in the Hello activity function code (Hello/__init__.py). Press F5 or select Debug: Start Debugging from the command palette to start the function app project. Output from Core Tools is displayed in the Terminal panel.

    [!NOTE] Refer to the Durable Functions Diagnostics for more information on debugging.

  2. Durable Functions requires an Azure Storage account to run. When VS Code prompts you to select a storage account, choose Select storage account.

    Create storage account

  3. Following the prompts, provide the following information to create a new storage account in Azure.

    Prompt Value Description
    Select subscription name of your subscription Select your Azure subscription
    Select a storage account Create a new storage account
    Enter the name of the new storage account unique name Name of the storage account to create
    Select a resource group unique name Name of the resource group to create
    Select a location region Select a region close to you

  4. In the Terminal panel, copy the URL endpoint of your HTTP-triggered function.

    Azure local output

  5. Using your browser, or a tool like Postman or cURL, send an HTTP request to the URL endpoint. Replace the last segment with the name of the orchestrator function (HelloOrchestrator). The URL should be similar to http://localhost:7071/api/orchestrators/HelloOrchestrator.

    The response is the initial result from the HTTP function letting you know the durable orchestration has started successfully. It is not yet the end result of the orchestration. The response includes a few useful URLs. For now, let's query the status of the orchestration.

  6. Copy the URL value for statusQueryGetUri and paste it in the browser's address bar and execute the request. Alternatively you can also continue to use Postman to issue the GET request.

    The request will query the orchestration instance for the status. You should get an eventual response, which shows the instance has completed, and includes the outputs or results of the durable function. It looks like:

    {
    "name": "HelloOrchestrator",
    "instanceId": "9a528a9e926f4b46b7d3deaa134b7e8a",
    "runtimeStatus": "Completed",
    "input": null,
    "customStatus": null,
    "output": [
        "Hello Tokyo!",
        "Hello Seattle!",
        "Hello London!"
    ],
    "createdTime": "2020-03-18T21:54:49Z",
    "lastUpdatedTime": "2020-03-18T21:54:54Z"
}

  7. To stop debugging, press Shift+F5 in VS Code.

After you've verified that the function runs correctly on your local computer, it's time to publish the project to Azure.

[!INCLUDE functions-create-function-app-vs-code]

[!INCLUDE functions-publish-project-vscode]

Test your function in Azure

  1. Copy the URL of the HTTP trigger from the Output panel. The URL that calls your HTTP-triggered function should be in this format: http://<functionappname>.azurewebsites.net/api/orchestrators/HelloOrchestrator

  2. Paste this new URL for the HTTP request into your browser's address bar. You should get the same status response as before when using the published app.

Next steps

You have used Visual Studio Code to create and publish a Python durable function app.

[!div class="nextstepaction"] Learn about common durable function patterns