Technical introduction to Azure Functions

/ 25 Jul, 2017
Azure Functions is Microsoft’s event-driven, serverless, cloud platform for creating lightweight background processes. It is Microsoft’s FaaS (Function as a Service) answer to Amazon’s AWS Lambda. A function is triggered by an event and many event triggers are built in the runtime. Azure Functions can be written in multiple programming languages.


In November 2014 Amazon introduced AWS Lambda. This service made Amazon into the first major cloud provider with a serverless offering. Besides Amazon, there are various other vendors of serverless offerings. Google is working on Google Cloud Functions, which has not been released yet. IBM offers a serverless platform within IBM Bluemix, which is called IBM OpenWhisk. In March 2016, Microsoft announced Azure Functions on Build, and Microsoft already released Azure Functions with General Availability (GA) as early as November 2016.

In Detail

Despite the term serverless, Azure Functions naturally needs servers to run on. The term serverless refers to the fact that you don’t need to provision or create virtual servers yourself to let the code run on. All necessary provisioning is done by Azure.

When you start with Azure Functions, you create a Functions app in the Azure Portal. This is the host of multiple functions, while a function app is a special kind of App Service: the portal provides a user interface to create functions and configures the triggers for it. It’s also possible to set up Continuous Integration with Azure Functions.

Azure functions are based on the Azure WebJobs SDK. The Azure WebJobs SDK offers triggers, bindings and a runtime. Triggers are events that trigger your function. Bindings are declared in metadata and connect external resources to your function as trigger, input or output parameters. Azure Functions offers a layer on top of this. This layer is open source and can be found on github. (

To create an Azure Function, you can choose one of the following programming languages: C#, PowerShell, Batch, Python, Bash, JavaScript, PHP or F#.

When you choose a C# based function, the function is created in a csx file, which  is a C# script file. When the function is executed for the first time, the script is compiled and executed in memory. You can compare an Azure Function with a method in a C# class. When you want to add other classes, these classes should be coded in the same csx file. It is not possible to separate files to put your code in. A result of this is that you have to think about what you automate in your Azure function and the amount of code that is needed for this. You should only have the code for the main process in your Azure Function to keep it maintainable. If you like, you can add references or Nuget packages to make use of Domain Models or other classes.

Pricing models

When you create an Azure Functions app, you can choose between two service plans: Consumption plan and App Service Plan.

The consumption plan is new and unique for Azure Functions. You only pay for the number of requests and the Gigabytes per second (GB-s). GB-s stands for the time required for processing, multiplied by the allocated memory. The price includes 1 million executions or 400.000 GB-s. The consumption plan scales the CPU and memory automatically up to 1.5 GB. It’s possible to configure a daily quota to create a limit on the spending.

The App Service Plan is the same Azure Resource you use to host your webapps or webjobs, for example a Standard S2. You pay for the entire service plan with fixed expenses, and you are in control of the scalability, which can have a fixed or automatic setup.

In addition to paying for Azure functions, you also need to pay for a Storage Account. All function types except HTTP triggers require a storage account.

Adding a function

After adding an Azure Function in the Azure Portal, the first thing you need to do is to choose the language you want to create the function in. After that, you choose how the function will be triggered, based on a predefined template (See all triggers in the table below). The last step consists of configuring the settings belonging to the selected trigger. For example, when you choose the Event Hub binding, you have to configure the access to the Event Hub. After the function has been added, the editor in the Azure portal offers functionality to develop, run and monitor the function.

Development environment in the Azure Portal


Azure Functions can be started on the basis of a trigger (event). Azure Functions can also integrate with other Azure Services, which is called bindings. The substantial power of Azure Functions becomes manifest through the integration with other Azure PaaS resources such as ServiceBus, Storage, and EventHub. The following table shows which triggers and bindings are supported with Azure Functions:

Function app Schedule

Triggers based on a schedule which is configured with a CRON expression

Http (REST or Webhook)

Invokes a function with an Http Request, responds to webhooks and allows to respond to requests. Like a GitHub webhook.

Blob Storage

Triggers for new and updated blobs in the container, read blobs or write blobs

Event Hub Event

Responds to an event send to the Event Hub or sends a message to the Event Hub

Storage Queue

Monitors a queue for new messages, responds to  them and writes messages to a storage queue

Service Bus Queue & Topic

Responds to messages from a queue or topic and creates a queue message

Table Storage

Stores read tables and writes entities

Mobile App Storage

Reads from and writes to data tables

Document DB

Reads or writes a document

Notification Hub Push notification

Sends push notifications

Twilio SMS

Sends an SMS text message


A trigger can be the event that starts the Azure Function. Please note that not all bindings support a trigger implementation. For example, it is not possible to start your Azure Function based on the event of a new document in DocumentDB. An Azure Function can only have one trigger and an unlimited number of inputs and outputs.

Bindings can be configured in the Azure Portal in a user-friendly user interface. The bindings are stored in the function.json file. This file can be edited in the Azure Portal also.

The binding for a trigger for an EventHub looks like this:

 "bindings": [
     "type": "eventHubTrigger",
     "name": "myEventHubMessage",
     "direction": "in",
     "path": "myeventhub",
     "connection": "ehconnection"
 "disabled": false

Local development

Since December 2016 it has been possible to develop functions locally in Visual Studio. To make this possible in Visual Studio you have to install The Visual Studio Tools for Azure Functions.

At the time of writing this article, this functionality is only available for Visual Studio 2015 update 3 and as yet, there is no version for Visual Studio 2017. The tools are a prerelease version and there are limitations. The most striking limitation is the limited support for IntelliSense in csx files. For example, there is no support from IntelliSense for input parameters.

The Azure Tools are offering a new Visual Studio Project template called Azure functions (prerelease). A project can contain multiple functions. The tooling also offers the same function templates as the Azure portal. Another major benefit of the tools is that it is possible to run Azure Functions locally and debug them.

When you debug a function for the first time, Visual Studio will ask you to download the Azure Function CLI. This CLI is needed to debug the Azure Function and acts locally as the host for the function. When an update is available, Visual Studio will ask you to download the latest version.

Running an Azure function locally with the Azure Function Tools


AppSettings and Connectionstrings work in the same way as Web Apps and Web Jobs. Similarly, the settings are stored in the application service. In the Azure Function Tools, appsettings and connectionstrings need to be added in the appsettings.json.

Settings on an Azure Function app.


Developing csx files is different from the normal way of developing C# classes. For example, it is not possible to set assembly references by setting a reference in the same way as you used to in Visual Studio.

To set dependencies to libraries it is possible to reference .Net 4.6 Nuget packages. These references are stored in the project.json file.

After that, you add the following line to the csx file:

#r “Microsoft.Azure.WebJobs”

It is also possible to reference your own assemblies. Add the assembly to the bin directory of the Azure Function and add a reference with the following line:

#r “MyAssemblyName.dll”


The latest feature at the time of writing this article is Azure Function Proxies. Proxies allow you to combine multiple Azure Functions in one large API. This large API is a façade, i.e. a single point of entry for the outside world and it forwards the calls to other Azure Functions. It is the light version of API Management, without throttling, security, and caching, with the benefit that it is cheaper.


With ScriptCS (csx files) it is not possible to unit test Azure Functions in Visual Studio. The functions can only be tested when the function runs in Azure.

Precompiled functions

One solution to make unit testing of functions easier is to use precompiled functions. With precompiled functions, you are actually developing the usual C# code instead of C# scripting code. This code is compiled into an assembly in the way you are used to. The compiled code can be deployed to Azure as an Azure Function. To do this, choose a Class Library project instead of an Azure Function project. This code can be tested in the same way you are used to. To let it behave as an Azure Function you need to add a couple of NuGet references,  and you need to add a function.json configuration file. A disadvantage of the precompiled function way of working is that you cannot edit the code in the Azure Portal anymore, because the file is in a binary format.

If you want to know more about this, please read the blogpost of our colleague Geert van der Cruijsen

Continuous Deployment

By default, the functions in the Azure Portal are not under source control. However, there are a number of options available to create integration with source control. Azure functions provide functionality to configure Continuous Deployment with several source code providers such as GitHub and VSTS. After configuration, the Azure Functions will be read-only in the Azure Portal. After each commit the entire Azure function app will be updated. However, you need to use separate branches if you want to be in control when a function app is deployed.

An Azure function becomes read only after configuring source control integration

Another possibility is to use a Build and Release pipeline in VSTS for example. You can read how to do this in the blogpost of our colleague Peter Groenewegen:


From a technical viewpoint, you can program the same functionality in C# with an Azure Function as with an Azure WebJob. One of the reasons why Azure Functions is interesting is the dynamic pricing model. You don’t have to pay any attention to any infrastructure dependency because you only pay for what you use and the first one million calls are free. In addition, the automatic scaling of pricing model is a powerful feature, which is another aspect that saves costs and makes your life easy. A final advantage of Azure Functions is that you don’t need to have an IDE (Visual Studio) to develop your functions. You only need a web browser!

Azure Functions force you to create small, self-contained pieces of functionality, which are event-driven and can be updated separately. These are characteristics of Micro services also. If you can handle the way you manage the source code, tests and updates this could be a neat approach. My experience is that Azure Functions already prove their power when using them to automate small separate processes like checking resources based on a timer or a different trigger.

Azure Functions provides you with more agility because you only have to consider business logic and not infrastructure. The Microsoft Azure Function team constantly updates the features for Azure Functions, so new functionality is on its way.

This article is part of XPRT. magazine.

Get your free copy or download XPRT. magazine