Azure Functions PowerShell developer guide

This article provides details about how you write Azure Functions using PowerShell.

Note

PowerShell for Azure Functions is currently in preview. To receive important updates, subscribe to the Azure App Service announcements repository on GitHub.

A PowerShell Azure function (function) is represented as a PowerShell script that executes when triggered. Each function script has a related function.json file that defines how the function behaves, such as how it's triggered and its input and output parameters. To learn more, see the Triggers and binding article.

Like other kinds of functions, PowerShell script functions take in parameters that match the names of all the input bindings defined in the function.json file. A TriggerMetadata parameter is also passed that contains additional information on the trigger that started the function.

This article assumes that you have already read the Azure Functions developer reference. You should have also completed the Functions quickstart for PowerShell to create your first PowerShell function.

Folder structure

The required folder structure for a PowerShell project looks like the following. This default can be changed. For more information, see the scriptFile section below.

PSFunctionApp
 | - MyFirstFunction
 | | - run.ps1
 | | - function.json
 | - MySecondFunction
 | | - run.ps1
 | | - function.json
 | - Modules
 | | - myFirstHelperModule
 | | | - myFirstHelperModule.psd1
 | | | - myFirstHelperModule.psm1
 | | - mySecondHelperModule
 | | | - mySecondHelperModule.psd1
 | | | - mySecondHelperModule.psm1
 | - local.settings.json
 | - host.json
 | - requirements.psd1
 | - profile.ps1
 | - extensions.csproj
 | - bin

At the root of the project, there's a shared host.json file that can be used to configure the function app. Each function has a folder with its own code file (.ps1) and binding configuration file (function.json). The name of the function.json file's parent directory is always the name of your function.

Certain bindings require the presence of an extensions.csproj file. Binding extensions, required in version 2.x of the Functions runtime, are defined in the extensions.csproj file, with the actual library files in the bin folder. When developing locally, you must register binding extensions. When developing functions in the Azure portal, this registration is done for you.

In PowerShell Function Apps, you may optionally have a profile.ps1 which runs when a function app starts to run (otherwise know as a cold start. For more information, see PowerShell profile.

Defining a PowerShell script as a function

By default, the Functions runtime looks for your function in run.ps1, where run.ps1 shares the same parent directory as its corresponding function.json.

Your script is passed a number of arguments on execution. To handle these parameters, add a param block to the top of your script as in the following example:

# $TriggerMetadata is optional here. If you don't need it, you can safely remove it from the param block
param($MyFirstInputBinding, $MySecondInputBinding, $TriggerMetadata)

TriggerMetadata parameter

The TriggerMetadata parameter is used to supply additional information about the trigger. The additional metadata varies from binding to binding but they all contain a sys property that contains the following data:

$TriggerMetadata.sys
Property Description Type
UtcNow When, in UTC, the function was triggered DateTime
MethodName The name of the Function that was triggered string
RandGuid a unique guid to this execution of the function string

Every trigger type has a different set of metadata. For example, the $TriggerMetadata for QueueTrigger contains the InsertionTime, Id, DequeueCount, among other things. For more information on the queue trigger's metadata, go to the official documentation for queue triggers. Check the documentation on the triggers you're working with to see what comes inside the trigger metadata.

Bindings

In PowerShell, bindings are configured and defined in a function's function.json. Functions interact with bindings a number of ways.

Reading trigger and input data

Trigger and input bindings are read as parameters passed to your function. Input bindings have a direction set to in in function.json. The name property defined in function.json is the name of the parameter, in the param block. Since PowerShell uses named parameters for binding, the order of the parameters doesn't matter. However, it's a best practice to follow the order of the bindings defined in the function.json.

param($MyFirstInputBinding, $MySecondInputBinding)

Writing output data

In Functions, an output binding has a direction set to out in the function.json. You can write to an output binding by using the Push-OutputBinding cmdlet, which is available to the Functions runtime. In all cases, the name property of the binding as defined in function.json corresponds to the Name parameter of the Push-OutputBinding cmdlet.

The following shows how to call Push-OutputBinding in your function script:

param($MyFirstInputBinding, $MySecondInputBinding)

Push-OutputBinding -Name myQueue -Value $myValue

You can also pass in a value for a specific binding through the pipeline.

param($MyFirstInputBinding, $MySecondInputBinding)

Produce-MyOutputValue | Push-OutputBinding -Name myQueue

Push-OutputBinding behaves differently based on the value specified for -Name:

  • When the specified name cannot be resolved to a valid output binding, then an error is thrown.

  • When the output binding accepts a collection of values, you can call Push-OutputBinding repeatedly to push multiple values.

  • When the output binding only accepts a singleton value, calling Push-OutputBinding a second time raises an error.

Push-OutputBinding syntax

The following are valid parameters for calling Push-OutputBinding:

Name Type Position Description
-Name String 1 The name of the output binding you want to set.
-Value Object 2 The value of the output binding you want to set, which is accepted from the pipeline ByValue.
-Clobber SwitchParameter Named (Optional) When specified, forces the value to be set for a specified output binding.

The following common parameters are also supported:

  • Verbose
  • Debug
  • ErrorAction
  • ErrorVariable
  • WarningAction
  • WarningVariable
  • OutBuffer
  • PipelineVariable
  • OutVariable

For more information, see About CommonParameters.

Push-OutputBinding example: HTTP responses

An HTTP trigger returns a response using an output binding named response. In the following example, the output binding of response has the value of "output #1":

PS >Push-OutputBinding -Name response -Value ([HttpResponseContext]@{
    StatusCode = [System.Net.HttpStatusCode]::OK
    Body = "output #1"
})

Because the output is to HTTP, which accepts a singleton value only, an error is thrown when Push-OutputBinding is called a second time.

PS >Push-OutputBinding -Name response -Value ([HttpResponseContext]@{
    StatusCode = [System.Net.HttpStatusCode]::OK
    Body = "output #2"
})

For outputs that only accept singleton values, you can use the -Clobber parameter to override the old value instead of trying to add to a collection. The following example assumes that you have already added a value. By using -Clobber, the response from the following example overrides the existing value to return a value of "output #3":

PS >Push-OutputBinding -Name response -Value ([HttpResponseContext]@{
    StatusCode = [System.Net.HttpStatusCode]::OK
    Body = "output #3"
}) -Clobber

Push-OutputBinding example: Queue output binding

Push-OutputBinding is used to send data to output bindings, such as an Azure Queue storage output binding. In the following example, the message written to the queue has a value of "output #1":

PS >Push-OutputBinding -Name outQueue -Value "output #1"

The output binding for a Storage queue accepts multiple output values. In this case, calling the following example after the first writes to the queue a list with two items: "output #1" and "output #2".

PS >Push-OutputBinding -Name outQueue -Value "output #2"

The following example, when called after the previous two, adds two more values to the output collection:

PS >Push-OutputBinding -Name outQueue -Value @("output #3", "output #4")

When written to the queue, the message contains these four values: "output #1", "output #2", "output #3", and "output #4".

Get-OutputBinding cmdlet

You can use the Get-OutputBinding cmdlet to retrieve the values currently set for your output bindings. This cmdlet retrieves a hashtable that contains the names of the output bindings with their respective values.

The following is an example of using Get-OutputBinding to return current binding values:

Get-OutputBinding
Name                           Value
----                           -----
MyQueue                        myData
MyOtherQueue                   myData

Get-OutputBinding also contains a parameter called -Name, which can be used to filter the returned binding, as in the following example:

Get-OutputBinding -Name MyQ*
Name                           Value
----                           -----
MyQueue                        myData

Wildcards (*) are supported in Get-OutputBinding.

Logging

Logging in PowerShell functions works like regular PowerShell logging. You can use the logging cmdlets to write to each output stream. Each cmdlet maps to a log level used by Functions.

Functions logging level Logging cmdlet
Error Write-Error
Warning Write-Warning
Information Write-Information
Write-Host
Write-Output
Information Writes to Information level logging.
Debug Write-Debug
Trace Write-Progress
Write-Verbose

In addition to these cmdlets, anything written to the pipeline is redirected to the Information log level and displayed with the default PowerShell formatting.

Important

Using the Write-Verbose or Write-Debug cmdlets is not enough to see verbose and debug level logging. You must also configure the log level threshold, which declares what level of logs you actually care about. To learn more, see Configure the function app log level.

Configure the function app log level

Azure Functions lets you define the threshold level to make it easy to control the way Functions writes to the logs. To set the threshold for all traces written to the console, use the logging.logLevel.default property in the host.json file. This setting applies to all functions in your function app.

The following example sets the threshold to enable verbose logging for all functions, but sets the threshold to enable debug logging for a function named MyFunction:

{
    "logging": {
        "logLevel": {
            "Function.MyFunction": "Debug",
            "default": "Trace"
        }
    }
}  

For more information, see host.json reference.

Viewing the logs

If your Function App is running in Azure, you can use Application Insights to monitor it. Read monitoring Azure Functions to learn more about viewing and querying function logs.

If you're running your Function App locally for development, logs default to the file system. To see the logs in the console, set the AZURE_FUNCTIONS_ENVIRONMENT environment variable to Development before starting the Function App.

Triggers and bindings types

There are a number of triggers and bindings available to you to use with your function app. The full list of triggers and bindings can be found here.

All triggers and bindings are represented in code as a few real data types:

  • Hashtable
  • string
  • byte[]
  • int
  • double
  • HttpRequestContext
  • HttpResponseContext

The first five types in this list are standard .NET types. The last two are used only by the HttpTrigger trigger.

Each binding parameter in your functions must be one of these types.

HTTP triggers and bindings

HTTP and webhook triggers and HTTP output bindings use request and response objects to represent the HTTP messaging.

Request object

The request object that's passed into the script is of the type HttpRequestContext, which has the following properties:

Property Description Type
Body An object that contains the body of the request. Body is serialized into the best type based on the data. For example, if the data is JSON, it's passed in as a hashtable. If the data is a string, it's passed in as a string. object
Headers A dictionary that contains the request headers. Dictionary<string,string>*
Method The HTTP method of the request. string
Params An object that contains the routing parameters of the request. Dictionary<string,string>*
Query An object that contains the query parameters. Dictionary<string,string>*
Url The URL of the request. string

* All Dictionary<string,string> keys are case-insensitive.

Response object

The response object that you should send back is of the type HttpResponseContext, which has the following properties:

Property Description Type
Body An object that contains the body of the response. object
ContentType A short hand for setting the content type for the response. string
Headers An object that contains the response headers. Dictionary or Hashtable
StatusCode The HTTP status code of the response. string or int

Accessing the request and response

When you work with HTTP triggers, you can access the HTTP request the same way you would with any other input binding. It's in the param block.

Use an HttpResponseContext object to return a response, as shown in the following:

function.json

{
  "bindings": [
    {
      "type": "httpTrigger",
      "direction": "in",
      "authLevel": "anonymous"
    },
    {
      "type": "http",
      "direction": "out"
    }
  ]
}

run.ps1

param($req, $TriggerMetadata)

$name = $req.Query.Name

Push-OutputBinding -Name res -Value ([HttpResponseContext]@{
    StatusCode = [System.Net.HttpStatusCode]::OK
    Body = "Hello $name!"
})

The result of invoking this function would be:

PS > irm http://localhost:5001?Name=Functions
Hello Functions!

Type-casting for triggers and bindings

For certain bindings like the blob binding, you're able to specify the type of the parameter.

For example, to have data from Blob storage supplied as a string, add the following type cast to my param block:

param([string] $myBlob)

PowerShell profile

In PowerShell, there's the concept of a PowerShell profile. If you're not familiar with PowerShell profiles, see About profiles.

In PowerShell Functions, the profile script executes when the function app starts. Function apps start when first deployed and after being idled (cold start).

When you create a function app using tools, such as Visual Studio Code and Azure Functions Core Tools, a default profile.ps1 is created for you. The default profile is maintained on the Core Tools GitHub repository and contains:

  • Automatic MSI authentication to Azure.
  • The ability to turn on the Azure PowerShell AzureRM PowerShell aliases if you would like.

PowerShell version

The following table shows the PowerShell version used by each major version of the Functions runtime:

Functions version PowerShell version
1.x Windows PowerShell 5.1 (locked by the runtime)
2.x PowerShell Core 6

You can see the current version by printing $PSVersionTable from any function.

Dependency management

PowerShell functions support managing Azure modules by the service. By modifying the host.json and setting the managedDependency enabled property to true, the requirements.psd1 file will be processed. The latest Azure modules will be automatically downloaded and made available to the function.

host.json

{
    "managedDependency": {
        "enabled": true
    }
}

requirements.psd1

@{
	Az = '1.*'
}

Leveraging your own custom modules or modules from the PowerShell Gallery is a little different than how you would do it normally.

When you install the module on your local machine, it goes in one of the globally available folders in your $env:PSModulePath. Since your function runs in Azure, you won't have access to the modules installed on your machine. This requires that the $env:PSModulePath for a PowerShell function app differs from $env:PSModulePath in a regular PowerShell script.

In Functions, PSModulePath contains two paths:

  • A Modules folder that exists at the root of your Function App.
  • A path to a Modules folder that lives inside the PowerShell language worker.

Function app-level Modules folder

To use custom modules or PowerShell modules from the PowerShell Gallery, you can place modules on which your functions depend in a Modules folder. From this folder, modules are automatically available to the functions runtime. Any function in the function app can use these modules.

To take advantage of this feature, create a Modules folder in the root of your function app. Save the modules you want to use in your functions in this location.

mkdir ./Modules
Save-Module MyGalleryModule -Path ./Modules

Use Save-Module to save all of the modules your functions use, or copy your own custom modules to the Modules folder. With a Modules folder, your function app should have the following folder structure:

PSFunctionApp
 | - MyFunction
 | | - run.ps1
 | | - function.json
 | - Modules
 | | - MyGalleryModule
 | | - MyOtherGalleryModule
 | | - MyCustomModule.psm1
 | - local.settings.json
 | - host.json

When you start your function app, the PowerShell language worker adds this Modules folder to the $env:PSModulePath so that you can rely on module autoloading just as you would in a regular PowerShell script.

Language worker level Modules folder

Several modules are commonly used by the PowerShell language worker. These modules are defined in the last position of PSModulePath.

The current list of modules is as follows:

  • Microsoft.PowerShell.Archive: module used for working with archives, like .zip, .nupkg, and others.
  • ThreadJob: A thread-based implementation of the PowerShell job APIs.

The most recent version of these modules is used by Functions. To use a specific version of these modules, you can put the specific version in the Modules folder of your function app.

Environment variables

In Functions, app settings, such as service connection strings, are exposed as environment variables during execution. You can access these settings using $env:NAME_OF_ENV_VAR, as shown in the following example:

param($myTimer)

Write-Host "PowerShell timer trigger function ran! $(Get-Date)"
Write-Host $env:AzureWebJobsStorage
Write-Host $env:WEBSITE_SITE_NAME

There are several ways that you can add, update, and delete function app settings:

When running locally, app settings are read from the local.settings.json project file.

Concurrency

By default, the Functions PowerShell runtime can only process one invocation of a function at a time. However, this concurrency level might not be sufficient in the following situations:

  • When you're trying to handle a large number of invocations at the same time.
  • When you have functions that invoke other functions inside the same function app.

You can change this behavior by setting the following environment variable to an integer value:

PSWorkerInProcConcurrencyUpperBound

You set this environment variable in the app settings of your Function App.

Considerations for using concurrency

PowerShell is a single threaded scripting language by default. However, concurrency can be added by using multiple PowerShell runspaces in the same process. This feature is how the Azure Functions PowerShell runtime works.

There are some drawbacks with this approach.

Concurrency is only as good as the machine it's running on

If your function app is running on an App Service plan that only supports a single core, then concurrency won't help much. That's because there are no additional cores to help balance the load. In this case, performance can vary when the single core has to context-switch between runspaces.

The Consumption plan runs using only one core, so you can't leverage concurrency. If you want to take full advantage of concurrency, instead deploy your functions to a function app running on a dedicated App Service plan with sufficient cores.

Azure PowerShell state

Azure PowerShell uses some process-level contexts and state to help save you from excess typing. However, if you turn on concurrency in your function app and invoke actions that change state, you could end up with race conditions. These race conditions are difficult to debug because one invocation relies on a certain state and the other invocation changed the state.

There's immense value in concurrency with Azure PowerShell, since some operations can take a considerable amount of time. However, you must proceed with caution. If you suspect that you're experiencing a race condition, set the concurrency back to 1 and try the request again.

Configure function scriptFile

By default, a PowerShell function is executed from run.ps1, a file that shares the same parent directory as its corresponding function.json.

The scriptFile property in the function.json can be used to get a folder structure that looks like the following example:

FunctionApp
 | - host.json
 | - myFunction
 | | - function.json
 | - lib
 | | - PSFunction.ps1

In this case, the function.json for myFunction includes a scriptFile property referencing the file with the exported function to run.

{
  "scriptFile": "../lib/PSFunction.ps1",
  "bindings": [
    // ...
  ]
}

Use PowerShell modules by configuring an entryPoint

This article has shown PowerShell functions in the default run.ps1 script file generated by the templates. However, you can also include your functions in PowerShell modules. You can reference your specific function code in the module by using the scriptFile and entryPoint fields in the function.json` configuration file.

In this case, entryPoint is the name of a function or cmdlet in the PowerShell module referenced in scriptFile.

Consider the following folder structure:

FunctionApp
 | - host.json
 | - myFunction
 | | - function.json
 | - lib
 | | - PSFunction.psm1

Where PSFunction.psm1 contains:

function Invoke-PSTestFunc {
    param($InputBinding, $TriggerMetadata)

    Push-OutputBinding -Name OutputBinding -Value "output"
}

Export-ModuleMember -Function "Invoke-PSTestFunc"

In this example, the configuration for myFunction includes a scriptFile property that references PSFunction.psm1, which is a PowerShell module in another folder. The entryPoint property references the Invoke-PSTestFunc function, which is the entry point in the module.

{
  "scriptFile": "../lib/PSFunction.psm1",
  "entryPoint": "Invoke-PSTestFunc",
  "bindings": [
    // ...
  ]
}

With this configuration, the Invoke-PSTestFunc gets executed exactly as a run.ps1 would.

Considerations for PowerShell functions

When you work with PowerShell functions, be aware of the considerations in the following sections.

Cold Start

When developing Azure Functions in the serverless hosting model, cold starts are a reality. Cold start refers to period of time it takes for your function app to start running to process a request. Cold start happens more frequently in the Consumption plan because your function app gets shut down during periods of inactivity.

Bundle modules instead of using Install-Module

Your script is run on every invocation. Avoid using Install-Module in your script. Instead use Save-Module before publishing so that your function doesn't have to waste time downloading the module. If cold starts are impacting your functions, consider deploying your function app to an App Service plan set to always on or to a Premium plan.

Next steps

For more information, see the following resources: