Author - Daniels Kenneth In category - Software development Publish time - 13 October 2022

The orchestrator is a function that describes the way and order actions are executed in code. First of all, if you’ve already created your Azure Function app, you need to add two NuGet references to your csproj file. These are Microsoft.Azure.Functions.Extensions and Microsoft.Extensions.DependencyInjection.

  • Yes exactly, it enables you to specify how something should be executed through a flow.
  • And when the first activity finishes, the Orchestrator Function wakes up and carries on from where it left off, calling the next activity in the workflow.
  • One, is that it means we never need to update a row in our data store, we simply append new rows.
  • And the answer is, that behind the scenes, the Durable Functions extension is making use of an Azure Storage account.
  • And if our functions don’t run at all, we pay nothing, unlike if our code was running on a virtual machine, which we’d have to pay for each month even if it was idle.
  • Note that the orchestrator function only supports C# and the durable functions extension guarantees at least once execution of the activity function.

In upcoming blog posts, we will discuss these scenarios with Azure Durable Functions. The state is managed for you, whenever a VM or process recycles you will not lose the state of your flow. As we can see, it has called our function, but we need it to pass a name parameter in the query string.


And it uses storage tables, to store the state of the orchestrations, or workflows, that are currently in progress. And the way that the state is stored, uses a technique called event sourcing. With event sourcing, rather than storing the current state, we store information about all the actions that led up to that state. One, is that it means we never need to update a row in our data store, we simply append new rows. And another one is that we have a full history of everything that happened, to get to this point, which is great for auditing, or diagnostic purposes. Fan-out/fan-in refers to the pattern of executing multiple functions in parallel and then waiting for all to finish.

What is a durable function?

Durable Functions is an extension of Azure Functions that lets you write stateful functions in a serverless compute environment. The extension lets you define stateful workflows by writing orchestrator functions and stateful entities by writing entity functions using the Azure Functions programming model.

There’s a local.settings.json file, and if we open this file, we can see the connection string, pointing at the Storage Emulator, that we can use, for local development and testing. And of course, there’s our example function, Function1.cs, which is just going to respond with a hello message, whenever we call it. Now, it’s going to prompt for the version of the Azure Functions Runtime, that we want to use.

Creating the Get Unique Items Activity

And having this present will allow us to create new Azure Functions apps from the File-New Project menu. So now we’ve got a basic idea, of what Azure Functions is, and what we mean by serverless.

So, an Orchestrator Function calls an Activity Function, and an Activity Function is simply, a regular Azure Function, that participates in a workflow. Activity Functions can receive input data from the Orchestrator Function and can return data to it. And the way we start an orchestration is with an OrchestrationClient binding. Any regular Azure Function can use this binding, to start a new orchestration, or to get information about an orchestration. Let’s look at an example, of how these various types of Azure Function work together, in a Durable Functions workflow.

Durable Functions for Python

The extension lets define stateful workflows in a new type of function called an orchestrator function. In case VM goes down, the platform also persists state, meaning when a VM needs to recycle were one of the activity functions was running. The service drops messages into Azure storage, writing history events to a history table, and thus keep track of all the state. The extension under the hood leverages the storage account, which you create when provisioning the Function App – meaning it is isolated from others and managed for you. We’re going to be building lots of Durable Functions in this article series.

What is the difference between Azure functions and durable functions?

Durable Functions is an extension of Azure Functions. You can use Durable Functions for stateful orchestration of function execution. A durable function app is a solution that's made up of different Azure functions. Functions can play different roles in a durable function orchestration.

Durable functions are what Microsoft is calling “orchestrator functions”. It’s an extension of Azure Functions and takes a series of functions and wraps them as a single, long transaction. It lets you write stateful functions and workflows on top of the normally stateless Azure Functions.

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