Create a custom probe for Azure Application Gateway by using PowerShell for Azure Resource Manager

In this article, you add a custom probe to an existing application gateway with PowerShell. Custom probes are useful for applications that have a specific health check page or for applications that do not provide a successful response on the default web application.

Prerequisite: Install the Azure PowerShell module

To perform the steps in this article, you need to install and configure the Azure PowerShell module. Be sure to complete all of the instructions. After the installation is finished, sign in to Azure and select your subscription.

Create an application gateway with a custom probe

Sign in and create resource group

1. Use Connect-AzAccount to authenticate.

   Connect-AzAccount
   

2. Get the subscriptions for the account.

   Get-AzSubscription
   

3. Choose which of your Azure subscriptions to use.

   Select-AzSubscription -Subscriptionid '{subscriptionGuid}'
   

4. Create a resource group. You can skip this step if you have an existing resource group.

   New-AzResourceGroup -Name appgw-rg -Location 'West US'
   

Azure Resource Manager requires that all resource groups specify a location. This location is used as the default location for resources in that resource group. Make sure that all commands to create an application gateway use the same resource group.

In the preceding example, we created a resource group called appgw-RG in location West US.

Create a virtual network and a subnet

The following example creates a virtual network and a subnet for the application gateway. Application gateway requires its own subnet for use. For this reason, the subnet created for the application gateway should be smaller than the address space of the VNET to allow for other subnets to be created and used.

# Assign the address range 10.0.0.0/24 to a subnet variable to be used to create a virtual network.
$subnet = New-AzVirtualNetworkSubnetConfig -Name subnet01 -AddressPrefix 10.0.0.0/24

# Create a virtual network named appgwvnet in resource group appgw-rg for the West US region using the prefix 10.0.0.0/16 with subnet 10.0.0.0/24.
$vnet = New-AzVirtualNetwork -Name appgwvnet -ResourceGroupName appgw-rg -Location 'West US' -AddressPrefix 10.0.0.0/16 -Subnet $subnet

# Assign a subnet variable for the next steps, which create an application gateway.
$subnet = $vnet.Subnets[0]

Create a public IP address for the frontend configuration

Create a public IP resource publicIP01 in resource group appgw-rg for the West US region. This example uses a public IP address for the frontend IP address of the application gateway. Application gateway requires the public IP address to have a dynamically created DNS name therefore the -DomainNameLabel cannot be specified during the creation of the public IP address.

$publicip = New-AzPublicIpAddress -ResourceGroupName appgw-rg -Name publicIP01 -Location 'West US' -AllocationMethod Dynamic

Create an application gateway

You set up all configuration items before creating the application gateway. The following example creates the configuration items that are needed for an application gateway resource.

# Creates an application gateway Frontend IP configuration named gatewayIP01
$gipconfig = New-AzApplicationGatewayIPConfiguration -Name gatewayIP01 -Subnet $subnet

#Creates a backend IP address pool named pool01 with IP addresses 134.170.185.46, 134.170.188.221, 134.170.185.50.
$pool = New-AzApplicationGatewayBackendAddressPool -Name pool01 -BackendIPAddresses 134.170.185.46, 134.170.188.221, 134.170.185.50

# Creates a probe that will check health at http://contoso.com/path/path.htm
$probe = New-AzApplicationGatewayProbeConfig -Name probe01 -Protocol Http -HostName 'contoso.com' -Path '/path/path.htm' -Interval 30 -Timeout 120 -UnhealthyThreshold 8

# Creates the backend http settings to be used. This component references the $probe created in the previous command.
$poolSetting = New-AzApplicationGatewayBackendHttpSettings -Name poolsetting01 -Port 80 -Protocol Http -CookieBasedAffinity Disabled -Probe $probe -RequestTimeout 80

# Creates a frontend port for the application gateway to listen on port 80 that will be used by the listener.
$fp = New-AzApplicationGatewayFrontendPort -Name frontendport01 -Port 80

# Creates a frontend IP configuration. This associates the $publicip variable defined previously with the frontend IP that will be used by the listener.
$fipconfig = New-AzApplicationGatewayFrontendIPConfig -Name fipconfig01 -PublicIPAddress $publicip

# Creates the listener. The listener is a combination of protocol and the frontend IP configuration $fipconfig and frontend port $fp created in previous steps.
$listener = New-AzApplicationGatewayHttpListener -Name listener01  -Protocol Http -FrontendIPConfiguration $fipconfig -FrontendPort $fp

# Creates the rule that routes traffic to the backend pools.  In this example we create a basic rule that uses the previous defined http settings and backend address pool.  It also associates the listener to the rule
$rule = New-AzApplicationGatewayRequestRoutingRule -Name rule01 -RuleType Basic -BackendHttpSettings $poolSetting -HttpListener $listener -BackendAddressPool $pool

# Sets the SKU of the application gateway, in this example we create a small standard application gateway with 2 instances.
$sku = New-AzApplicationGatewaySku -Name Standard_Small -Tier Standard -Capacity 2

# The final step creates the application gateway with all the previously defined components.
$appgw = New-AzApplicationGateway -Name appgwtest -ResourceGroupName appgw-rg -Location 'West US' -BackendAddressPools $pool -Probes $probe -BackendHttpSettingsCollection $poolSetting -FrontendIpConfigurations $fipconfig  -GatewayIpConfigurations $gipconfig -FrontendPorts $fp -HttpListeners $listener -RequestRoutingRules $rule -Sku $sku

Add a probe to an existing application gateway

The following code snippet adds a probe to an existing application gateway.

# Load the application gateway resource into a PowerShell variable by using Get-AzApplicationGateway.
$getgw =  Get-AzApplicationGateway -Name appgwtest -ResourceGroupName appgw-rg

# Create the probe object that will check health at http://contoso.com/path/path.htm
$probe = Add-AzApplicationGatewayProbeConfig -ApplicationGateway $getgw -Name probe01 -Protocol Http -HostName 'contoso.com' -Path '/path/custompath.htm' -Interval 30 -Timeout 120 -UnhealthyThreshold 8

# Set the backend HTTP settings to use the new probe
$getgw = Set-AzApplicationGatewayBackendHttpSettings -ApplicationGateway $getgw -Name $getgw.BackendHttpSettingsCollection.name -Port 80 -Protocol Http -CookieBasedAffinity Disabled -Probe $probe -RequestTimeout 120

# Save the application gateway with the configuration changes
Set-AzApplicationGateway -ApplicationGateway $getgw

Remove a probe from an existing application gateway

The following code snippet removes a probe from an existing application gateway.

# Load the application gateway resource into a PowerShell variable by using Get-AzApplicationGateway.
$getgw =  Get-AzApplicationGateway -Name appgwtest -ResourceGroupName appgw-rg

# Remove the probe from the application gateway configuration object
$getgw = Remove-AzApplicationGatewayProbeConfig -ApplicationGateway $getgw -Name $getgw.Probes.name

# Set the backend HTTP settings to remove the reference to the probe. The backend http settings now use the default probe
$getgw = Set-AzApplicationGatewayBackendHttpSettings -ApplicationGateway $getgw -Name $getgw.BackendHttpSettingsCollection.name -Port 80 -Protocol http -CookieBasedAffinity Disabled

# Save the application gateway with the configuration changes
Set-AzApplicationGateway -ApplicationGateway $getgw

Get application gateway DNS name

Once the gateway is created, the next step is to configure the front end for communication. When you're using a public IP address, application gateway requires a dynamically assigned DNS name, which is not friendly. To ensure end users can hit the application gateway a CNAME record can be used to point to the public endpoint of the application gateway. Configuring a custom domain name for in Azure. To do this, retrieve details of the application gateway and its associated IP/DNS name using the PublicIPAddress element attached to the application gateway. The application gateway's DNS name should be used to create a CNAME record, which points the two web applications to this DNS name. The use of A-records is not recommended since the VIP may change on restart of application gateway.

Get-AzPublicIpAddress -ResourceGroupName appgw-RG -Name publicIP01

Name                     : publicIP01
ResourceGroupName        : appgw-RG
Location                 : westus
Id                       : /subscriptions/<subscription_id>/resourceGroups/appgw-RG/providers/Microsoft.Network/publicIPAddresses/publicIP01
Etag                     : W/"00000d5b-54ed-4907-bae8-99bd5766d0e5"
ResourceGuid             : 00000000-0000-0000-0000-000000000000
ProvisioningState        : Succeeded
Tags                     : 
PublicIpAllocationMethod : Dynamic
IpAddress                : xx.xx.xxx.xx
PublicIpAddressVersion   : IPv4
IdleTimeoutInMinutes     : 4
IpConfiguration          : {
                                "Id": "/subscriptions/<subscription_id>/resourceGroups/appgw-RG/providers/Microsoft.Network/applicationGateways/appgwtest/frontendIP
                            Configurations/frontend1"
                            }
DnsSettings              : {
                                "Fqdn": "00000000-0000-xxxx-xxxx-xxxxxxxxxxxx.cloudapp.net"
                            }

Next steps

Learn to configure TLS offloading by visiting: Configure TLS Offload