Connecting Web Apps to external services – Virtual Appliance Walkthrough

Connecting Web Apps to external services – Virtual Appliance Walkthrough

For this purpose of this walkthrough it is assumed that the steps to establish a working Point to Site VPN have been completed. If you have also established a working Site to Site VPN following this walkthrough it will stop the it working correctly. The walkthrough assumes that the virtual network appliance is using the Barracuda NextGen Firewall F-Series virtual network appliance.

  1. Create an subnet in your VNET with the following settings Name:frontend and Address Range (CIDR Block) :
  2. Using the Azure MarketPlace create an instance of the virtual network appliance. This is a “Barracuda NextGen Firewall F-Series (PAYG)”. You will be charged for it use so you’ll want to ensure that these costs are factored into any planning. You are asked a number of things when setting this up. The important things for this walkthrough are that it is in its own resource group and it is connected to the frontend subnet you just created. Make a note of the password you use – it will be needed later.

Notice that you will be charge for the Barracuda License outside of any Azure Credit you might have.


  1. The Virtual Network Appliance needs to act as a network gateway, capturing traffic that is not address directly to it and forwarding it on to its destination. In order to do this IP forwarding needs to be enabled on the Network Interface for the Virtual Network Appliance.


  1. Create a Route Table that will route all Internet bound traffic to the virtual network appliance. In this example, I’m controlling the public IP so I’ll restrict the rule to just this IP. This means that I’ll still be able to connect to my VM over the Internet without issues. In production scenarios, you’ll have to think a bit harder about how the routes should be set up. Ensure that the route table is created in the network resource group.
  2. In the newly created route table create a route that routes traffic that needs to go through the virtual network appliance. Ensure that you have the following settings, Next Hop Type: Virtual Appliance & Next Hop Address: . If you are using a single IP remember you’ll still need to use CIDR notation. That means appending /32 to the end of the address.


  1. Assign the route table to the GatewaySubnet and the Backend Subnets.
  2. Through the service plan for the App Service, navigate to the networking option and then click to Manage the VNET Integration. Under the VNET Integration you need to add an entry to the IP ADDRESSES ROUTED TO VNET section. For this walkthrough you can set the start and end address to that of the external endpoint you are connecting to. For production scenarios use an appropriate address range. Take into consideration other services that the application might use, such as SQL Azure and Redis cache. By default all these connections are over the Internet so if you are not careful, you can route traffic for these connection into your VNET.


Configuring the Firewall

When the Firewall is setup up it will be secure by default and as such it will not know what to do with traffic destine to your external endpoint. Therefore, it will need to be configured to allow this traffic to flow. The Barracuda Firewall runs on Linux so connecting to it is a bit different to connected to a Windows machine. Luckily Barracuda provide a Windows Desktop application that takes away much of the pain.

  1. Download the Barracuda NextGen Admin application from the Barracuda website. You’ll need to create an account to achieve this.
  2. Once logged in go to Support -> Download and then select Barracuda NextGen Firewall project. On the resulting page select NextGen Admin as the Type and select the most recent version of the Barracuda NextGen Admin tool


  1. Run the NGAdmin tool and enter the public ip of the Virtual Network Appliance assigned to it by Azure. Then use Root of the username and enter the password you used when creating the appliance.


  1. The operation of the firewall software is broadly split into two roles. One for monitoring the system and the other for configuring it. If you click on the Firewall Tab at the top you’ll enter a screen that allows you to monitor firewall operations. From this screen you can do things such as seeing live and historic traffic cross the firewall and see what is allowed and what it blocked. On clicking the Forwarding Rules you can see how those access rules are defined. Luckily there is already a rule called LAN-2-INTERNET that manages access from the internal LAN (The Azure VNET in our case) and the Internet. The main problem is the software as it stands does not know the address ranges that represent our network. To change that we’ll have to use the configuration part of the software.


  1. Click on the configuration tab. The options to change the forwarding rules are very well hidden. Navigate to Box / Virtual Servers / S1 () [xxx] / Assigned Services / NGFW (Firewall) / Forwarding Rules


  1. On the resulting screen, you need to change the definition of the LAN-2-INTERNET rule. In the Source field you’ll find “ref: Trusted LAN”. If you drill into that by double clicking you’ll find that this in turn is defined as “Ref:Trusted LAN Networks” and “Ref:Trusted Next Hop Networks”. Again, by drilling in you’ll find that only “Ref: Trusted LAN Networks” is defined as This is not sufficient for our needs.


  1. This rule needs to allow traffic that originates both from our VNET and from the VPN clients used to establish the Point to Site VPN from the App Services to the VNET. In production scenarios it would make sense to create groups to represent these address ranges and add them to the list of references defined by “Ref:Trusted LAN”. However, to keep things simple the rule can be updated directly.
  2. Add the address ranges (Point to Site VPN Clients) and (VNET) as sources. Note that the software locks down the UI to avoid mistakes creeping in. Therefore, you must Unlock the UI (by clicking LOCK bizarrely).


  1. Activate the changes by clicking “Send Changes” then clicking on “Activation Pending” and finally the “Activate” button
  2. This should be enough to browse from a VM on the backend subnet to the external resource. You can see traffic flowing from the Firewall tab under History. If the firewall is blocking traffic you’ll also see it here.


Connecting Web Apps to external services – Building a Simulated On Premise Network

Connecting Web Apps to external services – Building a Simulated On Premise Network

I mentioned last time that to test out the system that has been building up over the last few posts you need a simulated on premise network.  I briefly outlined that is was possible to copy many of the steps taken to build up cloud network to act as an on-premise network.

However, when I did this for real I was learning Amazon Web Services (AWS). So, this was the perfect opportunity to test out what I had learnt. The rest of the post is a walk-through I what I set up.

I’m not going to cover how to set up a Amazon account so I assume you have already done this. Amazon is slightly less forgiving when it comes to accruing costs so it is your responsibly to ensure that you choose free or cheap resources and that you delete things when you are done.

Secondly the walk-through builds up an IaaS based implement. The reason I do this is that it is closer to what you’ll find when integrating with an on-premise network for real. It is often useful to be able to have enough of understanding of the moving parts so that you can have productive conversations with the engineers working with the on-premise systems whose help you’ll need.

This walk-through will configure an EC2 instance running Windows Server on a VPC in AWS. The Windows Server will be running Remote Access Services (RAS) configured to act as an VPN endpoint. I use a T2 Micro sized EC2 instance to keep within the Free Tier in AWS. Before you can complete these steps you need two things from Azure, that this the Public IP address of your VPN Gateway and the shared secret you used when setup the Site to Site VPN in Azure.

AWS Configuration

  1. Log into the AWS and open up the VPC options
  2. Use the “Start VPC Wizard” and create a “VPC with a Single Public Subnet”. Note that a public rather than private subnet is used to keep the network configure simple and to allow RDP access to the EC2 instance over the Internet. Once the VPN is set up communication will be via a private IP address.
  3. For the IP4 CIDR block use Give the VPC a name and use the same address range for the Public Subnet’s address range. The rest of the options can be left as their defaults.

Notice how similar this is to setting up an Azure VNET. AWS VPCs and Azure VNETs are equivalent. What the AWS VPC wizard does in the background is create an Internet Gateway and network routing which allows traffic from this subnet out on to the Internet.

Using the same address range for the VPC and the subnet is not something you’d do for real but it is enough for this demo.

  1. Open up the EC2 page and select Launch Instance
  2. From the list of Amazon Machine Images (AMI) select Microsoft Windows Server 2016 Base
  3. On the instance type page ensure t2 micro is selected, and click “Next: Configure Instance Details”
  4. On the Configure Instance Details page ensure that you change the network and subnet to the one created in Step 3. You also want to set Auto Assign Public IP to Enabled so we have the ability to RDP to the instance over the Internet. Everything else can be left at their default settings.
  5. Remember to either create or use an existing key pair in order to be able to get the EC2 instance’s Admin password.

It will take a few minutes for the instance to start and be at a state where you’ll be able to obtain the admin password. Once you have the password you’ll be able to RDP into it using the public IP it was assigned at startupaws1

  1. Your EC2 instance will be acting as a network gateway which will allow network traffic destine for other resources to flow through it. AWS doesn’t allow that by default, but it can be setup by disabling source/destination checking.


  1. Open RDP and connect to your windows EC2 instance as Administrator
  2. There is a script available here at that will install and configure RRAS on your server. It mentions Windows Server 2012 but it also works Windows Server 2016. It requires a few changes for the demo setup, so the updated script is included below.

# Windows Azure Virtual Network

# This configuration template applies to Microsoft RRAS running on Windows Server 2012 R2.

# It configures an IPSec VPN tunnel connecting your on-premise VPN device with the Azure gateway.

# !!! Please notice that we have the following restrictions in our support for RRAS:
# !!! 1. Only IKEv2 is currently supported
# !!! 2. Only route-based VPN configuration is supported.
# !!! 3. Admin priveleges are required in order to run this script

Function Invoke-WindowsApi(
    [string] $dllName,
    [Type] $returnType,
    [string] $methodName,
    [Type[]] $parameterTypes,
    [Object[]] $parameters
    ## Begin to build the dynamic assembly
    $domain = [AppDomain]::CurrentDomain
    $name = New-Object Reflection.AssemblyName 'PInvokeAssembly'
    $assembly = $domain.DefineDynamicAssembly($name, 'Run')
    $module = $assembly.DefineDynamicModule('PInvokeModule')
    $type = $module.DefineType('PInvokeType', "Public,BeforeFieldInit")

    $inputParameters = @()

    for($counter = 1; $counter -le $parameterTypes.Length; $counter++)
        $inputParameters += $parameters[$counter - 1]

    $method = $type.DefineMethod($methodName, Public,HideBySig,Static,PinvokeImpl',$returnType, $parameterTypes)

    ## Apply the P/Invoke constructor
    $ctor = [Runtime.InteropServices.DllImportAttribute].GetConstructor([string])
    $attr = New-Object Reflection.Emit.CustomAttributeBuilder $ctor, $dllName

    ## Create the temporary type, and invoke the method.
    $realType = $type.CreateType()

    $ret = $realType.InvokeMember($methodName, 'Public,Static,InvokeMethod', $null, $null, $inputParameters)

    return $ret

Function Set-PrivateProfileString(
    ## Prepare the parameter types and parameter values for the Invoke-WindowsApi script
    $parameterTypes = [string], [string], [string], [string]
    $parameters = [string] $category, [string] $key, [string] $value, [string] $file

    ## Invoke the API
    [void] (Invoke-WindowsApi "kernel32.dll" ([UInt32]) "WritePrivateProfileString" $parameterTypes $parameters)

# Install RRAS role
Import-Module ServerManager
Install-WindowsFeature RemoteAccess -IncludeManagementTools
Add-WindowsFeature -name Routing -IncludeManagementTools

# !!! NOTE: A reboot of the machine might be required here after which the script can be executed again.

# Install S2S VPN
Import-Module RemoteAccess
if ((Get-RemoteAccess).VpnS2SStatus -ne "Installed")
    Install-RemoteAccess -VpnType VpnS2S

# Add and configure S2S VPN interface

Add-VpnS2SInterface -Protocol IKEv2 -AuthenticationMethod PSKOnly -NumberOfTries 3 -ResponderAuthenticationMethod PSKOnly -Name -Destination -IPv4Subnet @("", "", "") -SharedSecret 1234567890ABC

Set-VpnServerIPsecConfiguration -EncryptionType MaximumEncryption

Set-VpnS2Sinterface -Name -InitiateConfigPayload $false -Force

# Set S2S VPN connection to be persistent by editing the router.pbk file (required admin priveleges)
Set-PrivateProfileString $env:windir\System32\ras\router.pbk "" "IdleDisconnectSeconds" "0"
Set-PrivateProfileString $env:windir\System32\ras\router.pbk "" "RedialOnLinkFailure" "1"

# Restart the RRAS service
Restart-Service RemoteAccess

# Dial-in to Azure gateway
Connect-VpnS2SInterface -Name

It is surprisingly difficult to highlight within a code block in WordPress so review the IP addresses in the calls Add-VpnS2SInterface, Set-VpnS2Sinterface and Set-PrivateProfileString carefully.

This script installs the RRAS feature. It then configures an interface which will allow traffic into the VPN. You need to define where the VPN will connect to, which is the Public IP address of your Virtual Network Gateway in Azure. You then need to define all the subnets that can be routed to via the VPN. In this case, we define the address range for the Gateway and Backend subnets. We also define the address pool for the Point to Site VPN. This will allow traffic that entered the on premise network from the App Services to flow back again. Finally, we use the same shared secret that set up on the Azure side.

  1. Once the script has run you can confirms its status via the powershell command Get-VpnS2SInterface -name | Format-List. The result should be something like this. Note that the ConnectionState will remind Disconnected until the Azure side is setup.


  1. You’ll need to set up routing rules which allows network traffic to flow correctly from the AWS VPC through the VPN connection. Open up the Route Table associated with the subnet you created and add the following routes. The routes tells AWS VPC to route traffic destine to the Azure VNET and App Services sitting at the end of the Point to Site VPN, through the EC2 instance running the AWS side of the VPN Gateway.


If you attempt to simulate an on-premise network in Azure by creating another VNET and VPN gateway and connecting that to the other side of the Site to Site VPN you also need equivalent routes.

At this point if you have completed the Site to Site VPN configuration on the Azure side you should be set. Check that the Azure side VPN connection is reporting Connected and rerun Get-VpnS2SInterface -name to see if the AWS side is happy.


Sometimes the RRAS service does not start correctly, so if you are having problems to run the command Connect-VpnS2SInterface -Name

Connecting Web Apps to external services – Verifying a Site to Site connection

Connecting Web Apps to external services – Verifying a Site to Site connection

In this post, I’ll walkthrough how you test this configuration. Therefore are few moving parts so I take this a step at a time checking each connection.

Build a Test “On Premise” endpoint in Azure

To have a working example you need to have a “on premise” network at which you can point your Site to Site VPN. You don’t need a physical on-premise network – you can simulate it. I have done this both in Amazon AWS and in Azure.

To do this in Azure you repeat the steps for creating a virtual network, adding a VPN gateway and then configuring the Site to Site VPN. To avoid going completely mad use separate and appropriately named resource groups. When setting up the cloud side of the Site to Site VPN you point it at the public IP of the simulated on-premise VPN endpoint and do the opposite when configuring the cloud side VPN endpoint. Remember to use the same shared secret.

There are two extra steps you must remember which are required to ensure traffic can get back to the Point to Site clients, e.g., your web application. They are easily forgotten and the solution won’t work without them.

  • On the Local Gateway as well as adding the address space of Cloud VNET also add the Address range for your Point to Site Clients.
  • Add a route table so node son the “On Premise” network know what to do with traffic destine for the Point to Site clients. The next hop should be the Virtual Network gateway on the “on premise” side”

You’ll also need to add a VM to the simulated “on premise” network in order to provide an endpoint to hit.

Deploy a test app to App Service

These are the instructions to deploy an application using Visual Studio 2017.

  • Clone the following repo.
  • Open this in Visual Studio
  • In Solution Explorer right click “Client” then select “Publish”
  • On the next screen ensure “Microsoft Azure App Service” is selected and select the option to “Select Existing”. [This assumes you created the web app described in a previous post.
  • Then click “Publish”
  • In the next screen select the appropriate subscription and Web App and click “OK”
  • This should return you to Visual Studio where the client is built and then deployed to the correct Web App.
  • Once this is completes a browser windows opens the web site you have just deployed. You see a screen as shown below. This error is there because we haven’t deployed the server yet, nor have we configured the client to connect to the correct server.


Deploy a Test app to VMs

These steps assume that you have a VM connected to the same Azure Virtual network that contains the VPN Gateway running your Point to Site VPN that is connecting to your Azure Web App.

  • Ensure that your VM has IIS setup and configured to running a .NET based Web Application
    • Install Web Server (IIS) Server Role
    • Add the Asp.NET 4.6 Feature
  • Disable IE Enhanced Security Configuration for Administrator
  • Build the Server project from the ConnectivityTest solution
  • Zip up the Server folder and copy onto the VM
  • Unzip the contents of the zip to C:\inetpub\wwwroot
  • Test the API is working by browsing to


Note that the response contains an IP address of ::1 for the caller. This is due to how the following code reports the IP of localhost. This reports the correct IP when the caller is not on the same machine as that hosting the API.

private string GetClientIp(HttpRequestMessage request = null)
    request = request ?? Request;

    if (request.Properties.ContainsKey("MS_HttpContext"))
        return ((HttpContextWrapper)request.Properties["MS_HttpContext"]).Request.UserHostAddress;
    else if (HttpContext.Current != null)
        return HttpContext.Current.Request.UserHostAddress;
        return null;

Repeat these steps for the VM deployed to the simulated On-premise network

Verify Connectivity from the Web App to VM Service

In order for the Web App to talk to the VM in your Azure VPN you need to updates it configuration so it directs traffic to the private IP address of the VM.  Locate your Web App in the Azure portal and in its Application setting blade create an App Setting called BaseApiUrl. This overwrites the web.config application setting of the same name. You can also override the Name app setting in the same way.


Now when you load your Web App you should see a web page like this. This proves the Web Application is routing traffic from the Web App, through your VNET and onto the VM by way of the Point to Site VPN.


Referring back to the network diagram helps understand the significance of the IP addresses.


The first IP in my example is the IP address of the caller which in this case represents the Web App. Remember you have no access to the infrastructure that Microsoft is using to host this so this isn’t the IP address of the server running the web app itself. So, what is this IP address? When you configured the Point to Site VPN you configured an address range such as  When Azure did its magic, it created a client that is used in the Point to Site VPN. So, the IP address,, is the address of the client and it is allocated from the client address range. Will it always be, maybe, maybe not. Will it always be an address from the range, yes it will. In fact, I have noticed that the IP of the client can change either side of a Web App restart.

The second IP address is the IP address of the server hosting the API. In this case it is the IP address of the VM sitting in the Azure VNET’s backend subnet. The address comes from the address range of the backend subnet that we use when setting up the subnet.

Verify Connectivity from the Web App to On premise

This step acts as the reveal. Over a number of point we have setup a bit a networking and two VPN connections. Whilst we have had to get our hands a bit dirty with a bit of network we haven’t had to get too intimate with network and routing details. And now if we go back to the Web App Application Settings and change the URL to the reflect the IP address of your on premise network the screen will change to show the IP address on the simulated on premise app server.

At this point you show now have an end to end working system.

Connecting Web Apps to external services – Site to Site VPN Walkthrough

Thanks for staying with me.

In this post I’ll be walking through the process for configuring a Site to Site VPN. This will be used to connect an on-premise network with the VNET that we have been building up in Azure. This will enable a Web Application hosted in Azure App Services to communicate to a web service endpoint hosted on premise entirely privately over firstly a Point to Site VPN connection and then a Site to Site VPN. In order to keep this post to the point I will only be discussing the work involved in connecting to the on premise network over a Site to Site connection. In a future post, I’ll describe the steps involved in creating a “Test” on premise network in order for you to see the Site to Site connection working in practice.

Lets revisit the summary diagram.


Whilst in this configuration your application only needs to know the private IP address of the endpoint on the on premise network, you’ll need more in order to configure the site to site VPN. This requires the public IP address of the VPN endpoint in the on premise network. Likewise, configuring this will require the public IP address of the VPN gateway you configured in Azure last time. Armed with the public IP address of your on premise VPN gateway follow the steps below.

  1. Select the Virtual Network Gateway that you created last time and select Connections.
  2. Add a Connection. Give the connection a name and set the Connection Type to Site-To-Site (IPSec). Ensure the correct Virtual Network Gateway is selected and populate the Shared Key (PSK) field. By definition this key is used on both sides of the connection. Make a note of it so you can set up the on premise side later.
  3. You need to create a Local Network Gateway. This is a logical representation of the VPN Gateway on premise. Give it a name and use the relevant Public IP. You must specific the address space for the on-premise network. That enables Azure to configure the network routing to ensure on-premise bound network traffic is routed through the Site to Site VPN.

vpn gateway

It may take a few moment for the connection to be made. Eventually you’ll see a status of Succeeded.

vpn gateway connected

Once you have a successful connection you should be able to test it. Azure handles adding a routing entry so network address that are not Internet routable nor on the VNET will be routed through the VPN to the on premise network. Therefore, from a VM on your Azure VNET you should be able to ping a VM running on your on premise network via it’s private IP. This will work in the other direction too. Be sure to configure firewalls and network security groups to allow ICMP traffic.

Once you have confirmed the connectivity you should be able to configure your web application to connect to the resource endpoint on premise. Again you may need to tweak firewalls and NSG settings but in principle the connectivity should work.