In this post I am going to talk about how we can enable/disable azure function using rest api. I am going to take example of compiled azure function but the logic applies to in portal function too. The logic can be used to update any app setting value.

Basics setting for Azure function

For compiled function the enable or disable can be controlled using attribute called Disable and the value is stored in appsetting file. Default value is false. See below code the attribute Disable added to the function method. The parameter ‘is_disabled’ controls the enable/disable of the function. We can choose any name for this param. You need to have the is_disabled key in appsetting with value true/false.

public static class TestFunction
{
        [Disable("is_disabled")]
        [FunctionName("TestFunction")]
        public static async Task Run([IoTHubTrigger("messages/events", Connection = "IoTEventHub")]EventData[] myIoTHubMessage, ILogger log)
        {
//your logic
  }
}

Appsetting on azure portal. : true means function is disabled false means function is enabled.

Enabling/Disabling Azure function Using code

The need for disabling the azure function can be use case basis but most prominent use case is the down processing is down and you want stop processing the data and reduce your bills and in case of Event Hub Trigger to avoid data loss by stopping the function and avoiding checkpoint increment.

To disable/enable basically we need to change the value in app.setting . It can be done with 3 lines of powershell code. But if you want to automate that and give it to other process so everything runs smooth then rest api is best way. I have tried with logic apps but its complex and lengthy to setup. We are going to use azure function rest api written in powershell to enable/disable intended function.

Powershell Script Standalone 

For using power-shell script you need to install azure cli on your local box which can be downloaded from https://docs.microsoft.com/en-us/cli/azure/install-azure-cli?view=azure-cli-latest

Script for updating app setting is_disabled value: The below script can be used to add/update any app-setting key value. You need to have service principle created if you want to run the power-shell script in non interactive mode. Link for creating service principle -> https://docs.microsoft.com/en-us/azure/active-directory/develop/howto-create-service-principal-portal

$isdisabled = true # change true or false as per your need.
az login --service-principal --username 'your-app-id' --password 'you-app-key' --tenant 'your-tenant-id'
$keyvalue='is_disabled'+'='+$isdisabled
az functionapp config appsettings set --resource-group 'your-resource-group' --name 'your-site-name' --settings $keyvalue

The above powershell can be run from local box but what if you want to automate this and give this to some other process like down process in azure function controlling the azure function depending on load. In case of high load it disables the function when load in low it enables the function back. For this kind of scenario we can use rest api written in azure function using powershell. I am going with azure function as it is easy and fast to create and test. And if you are wondering if azure function can be written in powershell then answer is yes. See below link -> https://www.brianbunke.com/blog/2018/02/27/powershell-in-azure-functions/ Imp: The function app needs to have run-time version 1 to use powershell scripting.

Azure function Code for enabling/Disabling the other Az Function

# POST method: $req
$requestBody = Get-Content $req -Raw | ConvertFrom-Json
$name = $requestBody.name
$isdisabled = $requestBody.isdisabled
$resourceGroup = $requestBody.resourceGroup

# GET method: each querystring parameter is its own variable
if ($req_query_name) 
{
    $name = $req_query_name  # function name you want to disable
}
if ($req_query_isdisabled) 
{
    $isdisabled = $req_query_isdisabled #flag indicating you want to enable or disable.
}
if ($req_query_resourcegroup) 
{
    $resourceGroup = $req_query_resourcegroup #resource group of function app
}

# login to the azure using service principal
$azureAplicationId ="Your-ServicePrinceple-Id"
$azureTenantId= "Your-Tenant-Id"
$azurePassword = ConvertTo-SecureString "Your-App-Key" -AsPlainText -Force
$psCred = New-Object System.Management.Automation.PSCredential($azureAplicationId , $azurePassword)
Add-AzureRmAccount -Credential $psCred -TenantId $azureTenantId  -ServicePrincipal

# Retrieve the web app setting 
$webApp = Get-AzureRMWebApp -ResourceGroupName $resourceGroup -Name $name
$appSettingList = $webApp.SiteConfig.AppSettings

$hash = @{}
ForEach ($kvp in $appSettingList) {
    $hash[$kvp.Name] = $kvp.Value
}

#update the value required
$hash['is_disabled'] = $isdisabled

#set the application setting.
Set-AzureRMWebApp -ResourceGroupName $resourceGroup -Name $name -AppSettings $hash 

Out-File -Encoding Ascii -FilePath $res -inputObject "App Setting Updated."

You can quickly test using azure portal using Test pane. That’s it from my side happy coding. Thanks for reading and would be happy to answer your questions.