Create and use an internal load balancer with an App Service environment

Azure App Service Environment is a deployment of Azure App Service into a subnet in an Azure virtual network (VNet). There are two ways to deploy an App Service environment (ASE):

  • With a VIP on an external IP address, often called an External ASE.
  • With a VIP on an internal IP address, often called an ILB ASE because the internal endpoint is an internal load balancer (ILB).

This article shows you how to create an ILB ASE. For an overview on the ASE, see Introduction to App Service environments. To learn how to create an External ASE, see Create an External ASE.

Overview

You can deploy an ASE with an internet-accessible endpoint or with an IP address in your VNet. To set the IP address to a VNet address, the ASE must be deployed with an ILB. When you deploy your ASE with an ILB, you must provide:

  • Your own domain that you use when you create your apps.
  • The certificate used for HTTPS.
  • DNS management for your domain.

In return, you can do things such as:

  • Host intranet applications securely in the cloud, which you access through a site-to-site or Azure ExpressRoute VPN.
  • Host apps in the cloud that aren't listed in public DNS servers.
  • Create internet-isolated back-end apps, which your front-end apps can securely integrate with.

Disabled functionality

There are some things that you can't do when you use an ILB ASE:

  • Use IP-based SSL.
  • Assign IP addresses to specific apps.
  • Buy and use a certificate with an app through the Azure portal. You can obtain certificates directly from a certificate authority and use them with your apps. You can't obtain them through the Azure portal.

Create an ILB ASE

To create an ILB ASE:

  1. In the Azure portal, select New > Web + Mobile > App Service Environment.

  2. Select your subscription.

  3. Select or create a resource group.

  4. Select or create a VNet.

  5. If you select an existing VNet, you need to create a subnet to hold the ASE. Make sure to set a subnet size large enough to accommodate any future growth of your ASE. We recommend a size of /25, which has 128 addresses and can handle a maximum-sized ASE. The minimum size you can select is a /28. After infrastructure needs, this size can be scaled to a maximum of 11 instances.

    • Go beyond the default maximum of 100 instances in your App Service plans.

    • Scale near 100 but with more rapid front-end scaling.

  6. Select Virtual Network/Location > Virtual Network Configuration. Set the VIP Type to Internal.

  7. Enter a domain name. This domain is the one used for apps created in this ASE. There are some restrictions. It can't be:

    • net

    • azurewebsites.net

    • p.azurewebsites.net

    • <asename>.p.azurewebsites.net

    The custom domain name used for apps and the domain name used by your ASE can't overlap. For an ILB ASE with the domain name contoso.com, you can't use custom domain names for your apps like:

    • www.contoso.com

    • abcd.def.contoso.com

    • abcd.contoso.com

    If you know the custom domain names for your apps, choose a domain for the ILB ASE that won’t have a conflict with those custom domain names. In this example, you can use something like contoso-internal.com for the domain of your ASE because that won't conflict with custom domain names that end in .contoso.com.

  8. Select OK, and then select Create.

    ASE creation

On the Virtual Network blade, there is a Virtual Network Configuration option. You can use it to select an External VIP or an Internal VIP. The default is External. If you select External, your ASE uses an internet-accessible VIP. If you select Internal, your ASE is configured with an ILB on an IP address within your VNet.

After you select Internal, the ability to add more IP addresses to your ASE is removed. Instead, you need to provide the domain of the ASE. In an ASE with an External VIP, the name of the ASE is used in the domain for apps created in that ASE.

If you set VIP Type to Internal, your ASE name is not used in the domain for the ASE. You specify the domain explicitly. If your domain is contoso.corp.net and you create an app in that ASE named timereporting, the URL for that app is timereporting.contoso.corp.net.

Create an app in an ILB ASE

You create an app in an ILB ASE in the same way that you create an app in an ASE normally.

  1. In the Azure portal, select New > Web + Mobile > Web or Mobile or API App.

  2. Enter the name of the app.

  3. Select the subscription.

  4. Select or create a resource group.

  5. Select or create an App Service plan. If you want to create a new App Service plan, select your ASE as the location. Select the worker pool where you want your App Service plan to be created. When you create the App Service plan, select your ASE as the location and the worker pool. When you specify the name of the app, the domain under your app name is replaced by the domain for your ASE.

  6. Select Create. If you want the app to appear on your dashboard, select the Pin to dashboard check box.

    App Service plan creation

    Under App name, the domain name is updated to reflect the domain of your ASE.

Post-ILB ASE creation validation

An ILB ASE is slightly different than the non-ILB ASE. As already noted, you need to manage your own DNS. You also have to provide your own certificate for HTTPS connections.

After you create your ASE, the domain name shows the domain you specified. A new item appears in the Setting menu called ILB Certificate. The ASE is created with a certificate that doesn't specify the ILB ASE domain. If you use the ASE with that certificate, your browser tells you that it's invalid. This certificate makes it easier to test HTTPS, but you need to upload your own certificate that's tied to your ILB ASE domain. This step is necessary regardless of whether your certificate is self-signed or acquired from a certificate authority.

ILB ASE domain name

Your ILB ASE needs a valid SSL certificate. Use internal certificate authorities, purchase a certificate from an external issuer, or use a self-signed certificate. Regardless of the source of the SSL certificate, the following certificate attributes need to be configured properly:

  • Subject: This attribute must be set to *.your-root-domain-here.
  • Subject Alternative Name: This attribute must include both *.your-root-domain-here and *.scm.your-root-domain-here. SSL connections to the SCM/Kudu site associated with each app use an address of the form your-app-name.scm.your-root-domain-here.

Convert/save the SSL certificate as a .pfx file. The .pfx file must include all intermediate and root certificates. Secure it with a password.

If you want to create a self-signed certificate, you can use the PowerShell commands here. Be sure to use your ILB ASE domain name instead of internal.contoso.com:

$certificate = New-SelfSignedCertificate -certstorelocation cert:\localmachine\my -dnsname "\*.internal-contoso.com","\*.scm.internal-contoso.com"

$certThumbprint = "cert:\localMachine\my\" +$certificate.Thumbprint
$password = ConvertTo-SecureString -String "CHANGETHISPASSWORD" -Force -AsPlainText

$fileName = "exportedcert.pfx" 
Export-PfxCertificate -cert $certThumbprint -FilePath $fileName -Password $password

The certificate that these PowerShell commands generate is flagged by browsers because the certificate wasn't created by a certificate authority that's in your browser's chain of trust. To get a certificate that your browser trusts, procure it from a commercial certificate authority in your browser's chain of trust.

Set ILB certificate

To upload your own certificates and test access:

  1. After the ASE is created, go to the ASE UI. Select ASE > Settings > ILB Certificate.

  2. To set the ILB certificate, select the certificate .pfx file and enter the password. This step takes some time to process. A message appears stating that an upload operation is in progress.

  3. Get the ILB address for your ASE. Select ASE > Properties > Virtual IP Address.

  4. Create a web app in your ASE after the ASE is created.

  5. Create a VM if you don't have one in that VNet.

    Note

    Don't try to create this VM in the same subnet as the ASE because it will fail or cause problems.

  6. Set the DNS for your ASE domain. You can use a wildcard with your domain in your DNS. To do some simple tests, edit the hosts file on your VM to set the web app name to the VIP IP address:

    a. If your ASE has the domain name .ilbase.com and you create the web app named mytestapp, it's addressed at mytestapp.ilbase.com. You then set mytestapp.ilbase.com to resolve to the ILB address. (On Windows, the hosts file is at C:\Windows\System32\drivers\etc\.)

    b. To test web deployment publishing or access to the advanced console, create a record for mytestapp.scm.ilbase.com.

  7. Use a browser on that VM and go to http://mytestapp.ilbase.com. (Or go to whatever your web app name is with your domain.)

  8. Use a browser on that VM and go to https://mytestapp.ilbase.com. If you use a self-signed certificate, accept the lack of security.

    The IP address for your ILB is listed under IP addresses. This list also has the IP addresses used by the external VIP and for inbound management traffic.

    ILB IP address

Web jobs, Functions and the ILB ASE

Both Functions and web jobs are supported on an ILB ASE but for the portal to work with them, you must have network access to the SCM site. This means your browser must either be on a host that is either in or connected to the virtual network.

When you use Azure Functions on an ILB ASE, you might get an error message that says "We are not able to retrieve your functions right now. Please try again later." This error occurs because the Functions UI leverages the SCM site over HTTPS and the root certificate is not in the browser chain of trust. Web jobs has a similar problem. To avoid this problem you can do one of the following:

  • Add the certificate to your trusted certificate store. This unblocks Edge and Internet Explorer.
  • Use Chrome and go to the SCM site first, accept the untrusted certificate and then go to the portal.
  • Use a commercial certificate that is in your browser chain of trust. This is the best option.

DNS configuration

When you use an External VIP, the DNS is managed by Azure. Any app created in your ASE is automatically added to Azure DNS, which is a public DNS. In an ILB ASE, you must manage your own DNS. For a given domain such as contoso.net, you need to create DNS A records in your DNS that point to your ILB address for:

  • *.contoso.net
  • *.scm.contoso.net

If your ILB ASE domain is used for multiple things outside this ASE, you might need to manage DNS on a per-app-name basis. This method is challenging because you need to add each new app name into your DNS when you create it. For this reason, we recommend that you use a dedicated domain.

Publish with an ILB ASE

For every app that's created, there are two endpoints. In an ILB ASE, you have <app name>.<ILB ASE Domain> and <app name>.scm.<ILB ASE Domain>.

The SCM site name takes you to the Kudu console, called the Advanced portal, within the Azure portal. The Kudu console lets you view environment variables, explore the disk, use a console, and much more. For more information, see Kudu console for Azure App Service.

In the multitenant App Service and in an External ASE, there's single sign-on between the Azure portal and the Kudu console. For the ILB ASE, however, you need to use your publishing credentials to sign into the Kudu console.

Internet-based CI systems, such as GitHub and Visual Studio Team Services, don't work with an ILB ASE because the publishing endpoint isn't internet accessible. Instead, you need to use a CI system that uses a pull model, such as Dropbox.

The publishing endpoints for apps in an ILB ASE use the domain that the ILB ASE was created with. This domain appears in the app's publishing profile and in the app's portal blade (Overview > Essentials and also Properties). If you have an ILB ASE with the subdomain contoso.net and an app named mytest, use mytest.contoso.net for FTP and mytest.scm.contoso.net for web deployment.

Couple an ILB ASE with a WAF device

Azure App Service provides many security measures that protect the system. They also help to determine whether an app was hacked. The best protection for a web application is to couple a hosting platform, such as Azure App Service, with a web application firewall (WAF). Because the ILB ASE has a network-isolated application endpoint, it's appropriate for such a use.

To learn more about how to configure your ILB ASE with a WAF device, see Configure a web application firewall with your App Service environment. This article shows how to use a Barracuda virtual appliance with your ASE. Another option is to use Azure Application Gateway. Application Gateway uses the OWASP core rules to secure any applications placed behind it. For more information about Application Gateway, see Introduction to the Azure web application firewall.

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