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Code and test Azure Functions locally

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While you're able to develop and test Azure Functions in the Azure portal, many developers prefer a local development experience. When you use Functions, using your favorite code editor and development tools to create and test functions on your local computer becomes easier. Your local functions can connect to live Azure services, and you can debug them on your local computer using the full Functions runtime.

This article provides links to specific development environments for your preferred language. It also provides some shared guidance for local development, such as working with the local.settings.json file.

Local development environments

The way in which you develop functions on your local computer depends on your language and tooling preferences. The environments in the following table support local development:

Environment Languages Description
Visual Studio Code C# (in-process)
C# (isolated worker process)
JavaScript
PowerShell
Python		 The Azure Functions extension for VS Code adds Functions support to VS Code. Requires the Core Tools. Supports development on Linux, macOS, and Windows, when using version 2.x of the Core Tools. To learn more, see Create your first function using Visual Studio Code.
Command prompt or terminal C# (in-process)
C# (isolated worker process)
JavaScript
PowerShell
Python		 Azure Functions Core Tools provides the core runtime and templates for creating functions, which enable local development. Version 2.x supports development on Linux, macOS, and Windows. All environments rely on Core Tools for the local Functions runtime.
Visual Studio C# (in-process)
C# (isolated worker process)		 The Azure Functions tools are included in the Azure development workload of Visual Studio, starting with Visual Studio 2019. Lets you compile functions in a class library and publish the .dll to Azure. Includes the Core Tools for local testing. To learn more, see Develop Azure Functions using Visual Studio.
Maven (various) Java Maven archetype supports Core Tools to enable development of Java functions. Version 2.x supports development on Linux, macOS, and Windows. To learn more, see Create your first function with Java and Maven. Also supports development using Eclipse and IntelliJ IDEA.

Note

Because of limitations on editing function code in the Azure portal, you should develop your functions locally and publish your code project to a function app in Azure. For more information, see Development limitations in the Azure portal

Each of these local development environments lets you create function app projects and use predefined function templates to create new functions. Each uses the Core Tools so that you can test and debug your functions against the real Functions runtime on your own machine just as you would any other app. You can also publish your function app project from any of these environments to Azure.

Local project files

A Functions project directory contains the following files in the project root folder, regardless of language:

File name Description
host.json To learn more, see the host.json reference.
local.settings.json Settings used by Core Tools when running locally, including app settings. To learn more, see local settings file.
.gitignore Prevents the local.settings.json file from being accidentally published to a Git repository. To learn more, see local settings file.
.vscode\extensions.json Settings file used when opening the project folder in Visual Studio Code.

Other files in the project depend on your language and specific functions. For more information, see the developer guide for your language.

Local settings file

The local.settings.json file stores app settings and settings used by local development tools. Settings in the local.settings.json file are used only when you're running your project locally. When you publish your project to Azure, be sure to also add any required settings to the app settings for the function app.

Important

Because the local.settings.json may contain secrets, such as connection strings, you should never store it in a remote repository. Tools that support Functions provide ways to synchronize settings in the local.settings.json file with the app settings in the function app to which your project is deployed.

The local settings file has this structure:

{
  "IsEncrypted": false,
  "Values": {
    "FUNCTIONS_WORKER_RUNTIME": "<language worker>",
    "AzureWebJobsStorage": "<connection-string>",
    "MyBindingConnection": "<binding-connection-string>",
    "AzureWebJobs.HttpExample.Disabled": "true"
  },
  "Host": {
    "LocalHttpPort": 7071,
    "CORS": "*",
    "CORSCredentials": false
  },
  "ConnectionStrings": {
    "SQLConnectionString": "<sqlclient-connection-string>"
  }
}

These settings are supported when you run projects locally:

Setting Description
IsEncrypted When this setting is set to true, all values are encrypted with a local machine key. Used with func settings commands. Default value is false. You might want to encrypt the local.settings.json file on your local computer when it contains secrets, such as service connection strings. The host automatically decrypts settings when it runs. Use the func settings decrypt command before trying to read locally encrypted settings.
Values Collection of application settings used when a project is running locally. These key-value (string-string) pairs correspond to application settings in your function app in Azure, like AzureWebJobsStorage. Many triggers and bindings have a property that refers to a connection string app setting, like Connection for the Blob storage trigger. For these properties, you need an application setting defined in the Values array. See the subsequent table for a list of commonly used settings.
Values must be strings and not JSON objects or arrays. Setting names can't include a double underline (__) and shouldn't include a colon (:). Double underline characters are reserved by the runtime, and the colon is reserved to support dependency injection.
Host Settings in this section customize the Functions host process when you run projects locally. These settings are separate from the host.json settings, which also apply when you run projects in Azure.
LocalHttpPort Sets the default port used when running the local Functions host (func host start and func run). The --port command-line option takes precedence over this setting. For example, when running in Visual Studio IDE, you may change the port number by navigating to the "Project Properties -> Debug" window and explicitly specifying the port number in a host start --port <your-port-number> command that can be supplied in the "Application Arguments" field.
CORS Defines the origins allowed for cross-origin resource sharing (CORS). Origins are supplied as a comma-separated list with no spaces. The wildcard value (*) is supported, which allows requests from any origin.
CORSCredentials When set to true, allows withCredentials requests.
ConnectionStrings A collection. Don't use this collection for the connection strings used by your function bindings. This collection is used only by frameworks that typically get connection strings from the ConnectionStrings section of a configuration file, like Entity Framework. Connection strings in this object are added to the environment with the provider type of System.Data.SqlClient. Items in this collection aren't published to Azure with other app settings. You must explicitly add these values to the Connection strings collection of your function app settings. If you're creating a SqlConnection in your function code, you should store the connection string value with your other connections in Application Settings in the portal.

The following application settings can be included in the Values array when running locally:

Setting Values Description
AzureWebJobsStorage Storage account connection string, or
UseDevelopmentStorage=true		 Contains the connection string for an Azure storage account. Required when using triggers other than HTTP. For more information, see the AzureWebJobsStorage reference.
When you have the Azurite Emulator installed locally and you set AzureWebJobsStorage to UseDevelopmentStorage=true, Core Tools uses the emulator. For more information, see Local storage emulator.
AzureWebJobs.<FUNCTION_NAME>.Disabled true|false To disable a function when running locally, add "AzureWebJobs.<FUNCTION_NAME>.Disabled": "true" to the collection, where <FUNCTION_NAME> is the name of the function. To learn more, see How to disable functions in Azure Functions.
FUNCTIONS_WORKER_RUNTIME dotnet
dotnet-isolated
node
java
powershell
python		 Indicates the targeted language of the Functions runtime. Required for version 2.x and higher of the Functions runtime. This setting is generated for your project by Core Tools. To learn more, see the FUNCTIONS_WORKER_RUNTIME reference.
FUNCTIONS_WORKER_RUNTIME_VERSION ~7 Indicates to use PowerShell 7 when running locally. If not set, then PowerShell Core 6 is used. This setting is only used when running locally. The PowerShell runtime version is determined by the powerShellVersion site configuration setting, when it runs in Azure, which can be set in the portal.

Synchronize settings

When you develop your functions locally, any local settings required by your app must also be present in app settings of the function app to which your code is deployed. You may also need to download current settings from the function app to your local project. While you can manually configure app settings in the Azure portal, the following tools also let you synchronize app settings with local settings in your project:

Triggers and bindings

When you develop your functions locally, you need to take trigger and binding behaviors into consideration. For HTTP triggers, you can simply call the HTTP endpoint on the local computer, using http://localhost/. For non-HTTP triggered functions, there are several options to run locally:

  • The easiest way to test bindings during local development is to use connection strings that target live Azure services. You can target live services by adding the appropriate connection string settings in the Values array in the local.settings.json file. When you do this, local executions during testing impact live service data. Because of this, consider setting-up separate services to use during development and testing, and then switch to different services during production.
  • For storage-based triggers, you can use a local storage emulator.
  • You can manually run non-HTTP trigger functions by using special administrator endpoints. For more information, see Manually run a non HTTP-triggered function.

During local testing, you must be running the host provided by Core Tools (func.exe) locally. For more information, see Azure Functions Core Tools.

HTTP test tools

During development, it's easy to call any of your function endpoints from a web browser when they support the HTTP GET method. However, for other HTTP methods that support payloads, such as POST or PUT, you need to use an HTTP test tool to create and send these HTTP requests to your function endpoints.

Caution

For scenarios where your requests must include sensitive data, make sure to use a tool that protects your data and reduces the risk of exposing any sensitive data to the public. Sensitive data you should protect might include: credentials, secrets, access tokens, API keys, geolocation data, even personally-identifiable information (PII).

You can keep your data secure by choosing an HTTP test tool that works either offline or locally, doesn't sync your data to the cloud, and doesn't require that you sign in to an online account. Some tools can also protect your data from accidental exposure by implementing specific security features.

Avoid using tools that centrally store your HTTP request history (including sensitive information), don't follow best security practices, or don't respect data privacy concerns.

Consider using one of these tools for securely sending HTTP requests to your function endpoints:

Local storage emulator

During local development, you can use the local Azurite emulator when testing functions with Azure Storage bindings (Queue Storage, Blob Storage, and Table Storage), without having to connect to remote storage services. Azurite integrates with Visual Studio Code and Visual Studio, and you can also run it from the command prompt using npm. For more information, see Use the Azurite emulator for local Azure Storage development.

The following setting in the Values collection of the local.settings.json file tells the local Functions host to use Azurite for the default AzureWebJobsStorage connection:

"AzureWebJobsStorage": "UseDevelopmentStorage=true"

With this setting value, any Azure Storage trigger or binding that uses AzureWebJobsStorage as its connection connects to Azurite when running locally. Keep these considerations in mind when using storage emulation during local execution:

  • You must have Azurite installed and running.
  • You should test with an actual storage connection to Azure services before publishing to Azure.
  • When you publish your project, don't publish the AzureWebJobsStorage setting as UseDevelopmentStorage=true. In Azure, the AzureWebJobsStorage setting must always be the connection string of the storage account used by your function app. For more information, see AzureWebJobsStorage.

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