Azure Functions developer guide

• 10/12/2017
• 6 minutes to read
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In Azure Functions, specific functions share a few core technical concepts and components, regardless of the language or binding you use. Before you jump into learning details specific to a given language or binding, be sure to read through this overview that applies to all of them.

This article assumes that you've already read the Azure Functions overview.

Function code

A function is the primary concept in Azure Functions. A function contains two important pieces - your code, which can be written in a variety of languages, and some config, the function.json file. For compiled languages, this config file is generated automatically from annotations in your code. For scripting languages, you must provide the config file yourself.

The function.json file defines the function's trigger, bindings, and other configuration settings. Every function has one and only one trigger. The runtime uses this config file to determine the events to monitor and how to pass data into and return data from a function execution. The following is an example function.json file.

{
    "disabled":false,
    "bindings":[
        // ... bindings here
        {
            "type": "bindingType",
            "direction": "in",
            "name": "myParamName",
            // ... more depending on binding
        }
    ]
}

For more information, see Azure Functions triggers and bindings concepts.

The bindings property is where you configure both triggers and bindings. Each binding shares a few common settings and some settings which are specific to a particular type of binding. Every binding requires the following settings:

Function app

A function app provides an execution context in Azure in which your functions run. As such, it is the unit of deployment and management for your functions. A function app is comprised of one or more individual functions that are managed, deployed, and scaled together. All of the functions in a function app share the same pricing plan, deployment method, and runtime version. Think of a function app as a way to organize and collectively manage your functions. To learn more, see How to manage a function app.

Folder structure

The code for all the functions in a specific function app is located in a root project folder that contains a host configuration file and one or more subfolders. Each subfolder contains the code for a separate function. The folder structure is shown in the following representation:

FunctionApp
 | - host.json
 | - MyFirstFunction
 | | - function.json
 | | - ...  
 | - MySecondFunction
 | | - function.json
 | | - ...  
 | - SharedCode
 | - bin

In version 2.x and higher of the Functions runtime, all functions in the function app must share the same language stack.

The host.json file contains runtime-specific configurations and is in the root folder of the function app. A bin folder contains packages and other library files that the function app requires. See the language-specific requirements for a function app project:

• C# class library (.csproj)
• C# script (.csx)
• F# script
• Java
• JavaScript
• Python

The above is the default (and recommended) folder structure for a Function app. If you wish to change the file location of a function's code, modify the scriptFile section of the function.json file. We also recommend using package deployment to deploy your project to your function app in Azure. You can also use existing tools like continuous integration and deployment and Azure DevOps.

Use local tools and publishing

Function apps can be authored and published using a variety of tools, including Visual Studio, Visual Studio Code, IntelliJ, Eclipse, and the Azure Functions Core Tools. For more information, see Code and test Azure Functions locally.

How to edit functions in the Azure portal

The Functions editor built into the Azure portal lets you update your code and your function.json file directly inline. This is recommended only for small changes or proofs of concept - best practice is to use a local development tool like VS Code.

Parallel execution

When multiple triggering events occur faster than a single-threaded function runtime can process them, the runtime may invoke the function multiple times in parallel. If a function app is using the Consumption hosting plan, the function app could scale out automatically. Each instance of the function app, whether the app runs on the Consumption hosting plan or a regular App Service hosting plan, might process concurrent function invocations in parallel using multiple threads. The maximum number of concurrent function invocations in each function app instance varies based on the type of trigger being used as well as the resources used by other functions within the function app.

Functions runtime versioning

You can configure the version of the Functions runtime using the FUNCTIONS_EXTENSION_VERSION app setting. For example, the value "~3" indicates that your function app will use 3.x as its major version. Function apps are upgraded to each new minor version as they are released. For more information, including how to view the exact version of your function app, see How to target Azure Functions runtime versions.

Repositories

The code for Azure Functions is open source and stored in GitHub repositories:

• Azure Functions
• Azure Functions host
• Azure Functions portal
• Azure Functions templates
• Azure WebJobs SDK
• Azure WebJobs SDK Extensions

Bindings

Here is a table of all supported bindings.

This table shows the bindings that are supported in the major versions of the Azure Functions runtime:

¹ Starting with the version 2.x runtime, all bindings except HTTP and Timer must be registered. See Register binding extensions.

² Triggers aren't supported in the Consumption plan. Requires runtime-driven triggers.

³ Supported only in Kubernetes, IoT Edge, and other self-hosted modes only.

Having issues with errors coming from the bindings? Review the Azure Functions Binding Error Codes documentation.

Reporting Issues

Next steps

For more information, see the following resources:

• Azure Functions triggers and bindings
• Code and test Azure Functions locally
• Best Practices for Azure Functions
• Azure Functions C# developer reference
• Azure Functions Node.js developer reference