How can i list the different instances of a Azure app service and restart an instance?

Question

I have a app service in Azure that has been scaled out to 5 instances. I can list the instances via the following az cli command

   az webapp list-instances

But how can i tell which instance has frozen or is not responding and restart it ?

Answer 1

Here is some powershell to call the REST API to fetch a list of instances, and call a health probe on each one:

## 1. define environment
$subscriptionId = "redacted";
$resourceGroup = "redacted";
$webAppName = "redacted";

$staging = $false

# 2. get a list of instances:

$token = Get-AzAccessToken;
$RequestHeader = @{
    Authorization  = "Bearer $($token.Token)";
    'Content-Type' = "application/json";
}
if ($staging) {
    $instancesUrl = "https://management.azure.com/subscriptions/$($subscriptionId)/resourcegroups/$($resourceGroup)/providers/Microsoft.Web/sites/$($webAppName)/slots/staging/instances?api-version=2022-03-01";
} else {
    $instancesUrl = "https://management.azure.com/subscriptions/$($subscriptionId)/resourcegroups/$($resourceGroup)/providers/Microsoft.Web/sites/$($webAppName)/instances?api-version=2022-03-01";
}

Invoke-RestMethod -Headers $RequestHeader -Uri $instancesUrl | Select-Object -ExpandProperty value | Select-Object -ExpandProperty properties;

# 2. do a health-check on each instance:

$instances = Invoke-RestMethod -Headers $RequestHeader -Uri $instancesUrl | Select-Object -ExpandProperty value | Select-Object -ExpandProperty properties;

$webAppDomain = "$($webAppName).azurewebsites.net";
$webAppUrl = "https://$($webAppDomain)/healthprobe.html";

foreach ($instance in $instances)
{
    $instanceId = $instance.Name
    "Going to check healthprobe URL on instance $($instanceId)";
    $s = New-Object Microsoft.PowerShell.Commands.WebRequestSession
    $c = New-Object System.Net.Cookie('ARRAffinity',$instanceId,'/',$webAppDomain)
    $s.Cookies.Add($c)
    Invoke-WebRequest -UseBasicParsing -Method Get -Uri $webAppUrl -WebSession $s
}