Using Azure DNS for Dynamic DNS with PowerShell

I’ve been using DynDNS and other Free DNS Services for some time, but as they are getting harder and harder to use for free. Like you need to remember to logon and click a button once a month and what not. I figured it was time to migrate to Azure DNS instead. Being able to use PowerShell to handle my DNS together with everything I’ve already automated makes my life so much easier. And as I’ve already got a couple of domains and some Azure subscriptions there was more or less no increased cost for me. As you can see in the picture, Azure DNS Pricing is really cheap.

I’ve used Task Scheduler to scheduled the script below to run at Computer Startup on one of my Hyper-V Hosts at home, and then every hour. That guarantees that if there is a power failure and I get a new IP from my ISP, when the server boots, the external DNS pointers will be updated at once and just to be sure check every hour.

In short, the script checks your External IP and compares that to the IP of the hostname you want updated. If they are not identical, it will logon to Azure and update the hostname with your current IP.
Simple as that.

In my case, I’ve setup a UserName in AzureDNS who has access to just that DNSZone and are using that UserName in the script.

# Author Markus Lassfolk @ TrueSec 
# www.isolation.se   
# with some 'inspiration' from other scripts. 
#
# You need to have AzureRM modules installed to run this script
# https://docs.microsoft.com/en-us/powershell/azure/install-azurerm-ps
# install-module AzureRM 
#
# Set your ZoneInfo and Azure settings 
$ZoneName = "isolation.se"
$HostName = "home" 

$azurelogin ="username@azureAD.onmicrosoft.com"
$azurepassword = "password"
$azureResourceGroup = "ResourceGroup"


# Don't modify below this
#
Import-Module AzureRM 
Import-Module AzureRM.Dns 

function get-myexternalip() {   
    $urls = "http://whatismyip.akamai.com",  
            "http://b10m.swal.org/cgi-bin/whatsmyip.cgi?just-ip",  
            "http://icanhazip.com",  
            "http://www.whatismyip.org/"; 
 
           $RxIP = "(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})"; 
           $ip = "Unknown"; 
           Foreach ($address in $urls) { 
               try { 
                    $temp = wget $address; 
                    $www_content = $temp.Content; 
                    if ( $www_content -match $RxIP ) { 
                        $ip = ([regex]($rxip)).match($www_content).Value 
                        break 
                    } 
               } catch { continue } 
           } 
    return $ip 
}
 

# Set the expected IP Address. Obtain this from a DNS query or set it statically.
$EI = [System.Net.Dns]::GetHostAddresses($HostName +"."+ $ZoneName) | Select-Object -ExpandProperty IPAddressToString

# Obtain the IP Address of the Internet connection.
$CheckNetwork = Test-NetConnection -CommonTCPPort HTTP freegeoip.net
if ($CheckNetwork.TcpTestSucceeded -eq $True) { 
    $ExternalIP = get-myexternalip
$IP = $ExternalIP


# If the external IP is not the same as for the HostName 
If ($IP -ne $EI) {

    $accountName = $azurelogin
    $password = ConvertTo-SecureString $azurepassword -AsPlainText -Force
    $credential = New-Object System.Management.Automation.PSCredential($accountName, $password)

    # Login to Azure
    Login-AzureRmAccount -Credential $credential 
    Select-AzureRmSubscription -SubscriptionObject $(Get-AzureRmSubscription)

    # Set IP for the HostName 
    New-AzureRmDnsRecordSet -Name $HostName -RecordType A -ZoneName $ZoneName -ResourceGroupName $azureResourceGroup -Ttl 600 -DnsRecords (New-AzureRmDnsRecordConfig -IPv4Address "$($IP)") -Overwrite -Confirm:$false

}
Else {
    Write-Output "Dynamic address ($IP) and DNS address ($EI) match."
}

}

# Author Markus Lassfolk @ TrueSec

# www.isolation.se

# with some 'inspiration' from other scripts.

# You need to have AzureRM modules installed to run this script

# https://docs.microsoft.com/en-us/powershell/azure/install-azurerm-ps

# install-module AzureRM

# Set your ZoneInfo and Azure settings

$ZoneName = "isolation.se"

$HostName = "home"

$azurelogin ="username@azureAD.onmicrosoft.com"

$azurepassword = "password"

$azureResourceGroup = "ResourceGroup"

# Don't modify below this

Import-Module AzureRM

Import-Module AzureRM.Dns

function get-myexternalip() {

$urls = "http://whatismyip.akamai.com",

"http://b10m.swal.org/cgi-bin/whatsmyip.cgi?just-ip",

"http://icanhazip.com",

"http://www.whatismyip.org/";

$RxIP = "(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})";

$ip = "Unknown";

Foreach ($address in $urls) {

try {

$temp = wget $address;

$www_content = $temp.Content;

if ( $www_content -match $RxIP ) {

$ip = ([regex]($rxip)).match($www_content).Value

break

}

} catch { continue }

}

return $ip

}

# Set the expected IP Address. Obtain this from a DNS query or set it statically.

$EI = [System.Net.Dns]::GetHostAddresses($HostName +"."+ $ZoneName) | Select-Object -ExpandProperty IPAddressToString

# Obtain the IP Address of the Internet connection.

$CheckNetwork = Test-NetConnection -CommonTCPPort HTTP freegeoip.net

if ($CheckNetwork.TcpTestSucceeded -eq $True) {

$ExternalIP = get-myexternalip

$IP = $ExternalIP

# If the external IP is not the same as for the HostName

If ($IP -ne $EI) {

$accountName = $azurelogin

$password = ConvertTo-SecureString $azurepassword -AsPlainText -Force

$credential = New-Object System.Management.Automation.PSCredential($accountName, $password)

# Login to Azure

Select-AzureRmSubscription -SubscriptionObject $(Get-AzureRmSubscription)

# Set IP for the HostName

New-AzureRmDnsRecordSet -Name $HostName -RecordType A -ZoneName $ZoneName -ResourceGroupName $azureResourceGroup -Ttl 600 -DnsRecords (New-AzureRmDnsRecordConfig -IPv4Address "$($IP)") -Overwrite -Confirm:$false

}

Else {

Write-Output "Dynamic address ($IP) and DNS address ($EI) match."

}

You obviously need to migrate an existing or register a new DNS Zone to Azure and use Microsoft’s NameServers for this to work.

Using Azure DNS for Dynamic DNS with PowerShell

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