Host load-balanced Azure web apps at the zone apex

The DNS protocol prevents the assignment of a CNAME record at the zone apex. An example zone apex is contoso.com. This restriction presents a problem for application owners who have load-balanced applications behind Traffic Manager, because a Traffic Manager profile is normally referenced with a CNAME record. Pointing at the Traffic Manager profile from the zone apex record isn't possible with a CNAME record. As a result, application owners must use a workaround. A redirect at the application layer must redirect from the zone apex to another domain. An example is a redirect from contoso.com to www.contoso.com. This arrangement presents a single point of failure for the redirect function.

With alias records, you no longer will have this problem. You can point your zone apex record to a Traffic Manager profile that has external endpoints. You can also point to the same Traffic Manager profile used for other domains within the DNS zone.

For example, you can point contoso.com and www.contoso.com to the same Traffic Manager profile. This set up will work as long as the Traffic Manager profile has only external endpoints configured.

In this article, you learn how to create an alias record for your domain apex. Then you'll configure your Traffic Manager profile end points for your web apps.

If you don’t have an Azure subscription, create a free account before you begin.

Prerequisites

You must have a domain name available that you can host in Azure DNS to test with. You must have full control of this domain. Full control includes the ability to set the name server (NS) records for the domain.

For instructions to host your domain in Azure DNS, see Tutorial: Host your domain in Azure DNS.

The example domain used for this tutorial is contoso.com, but use your own domain name.

Create a resource group

Create a resource group to hold all the resources used in this article.

Create App Service plans

Create two Web App service plans in your resource group. Use the following table to help you configure this set up. For more information about creating an App Service plan, see Manage an App Service plan in Azure.

Name	Operating System	Location	Pricing Tier
ASP-01	Windows	East US	Dev/Test D1-Shared
ASP-02	Windows	Central US	Dev/Test D1-Shared

Create App Services

Create two web apps, one in each App Service plan.

1. On upper left corner of the Azure portal page, select Create a resource.

2. Type Web app in the search bar and press Enter.

3. Select Web App.

4. Select Create.

5. Accept the defaults, and use the following table to configure the two web apps:

   Name (must be unique within .azurewebsites.net)	Resource Group	Runtime stack	Region	App Service Plan/Location
   App-01	Use existing Select your resource group	.NET Core 2.2	East US	ASP-01(D1)
   App-02	Use existing Select your resource group	.NET Core 2.2	Central US	ASP-02(D1)

Gather some details

Now you need to note the IP address and host name for the web apps.

1. Open your resource group and select your first web app (App-01 in this example).
2. In the left column, select Properties.
3. Note the address under URL, and under Outbound IP Addresses note the first IP address in the list. You'll use this information later when you configure your Traffic Manager end points.
4. Repeat for App-02.

Create a Traffic Manager profile

Create a Traffic Manager profile in your resource group. Use the defaults and type a unique name within the trafficmanager.net namespace.

For more information, see Quickstart: Create a Traffic Manager profile for a highly available web application.

Create endpoints

Now you can create the endpoints for the two web apps.

1. Open your resource group and select your Traffic Manager profile.

2. In the left column, select Endpoints.

3. Select Add.

4. Use the following table to configure the endpoints:

   Type	Name	Target	Location	Custom Header settings
   External endpoint	End-01	IP address you recorded for App-01	East US	host:<the URL you recorded for App-01> Example: host:app-01.azurewebsites.net
   External endpoint	End-02	IP address you recorded for App-02	Central US	host:<the URL you recorded for App-02> Example: host:app-02.azurewebsites.net

Create DNS zone

You can either use an existing DNS zone for testing, or you can create a new zone. To create and delegate a new DNS zone in Azure, see Tutorial: Host your domain in Azure DNS.

Add a TXT record for custom domain validation

When you add a custom hostname to your web apps, it will look for a specific TXT record to validate your domain.

1. Open your resource group and select the DNS zone.

2. Select Record set.

3. Add the record set using the following table. For the value, use the actual web app URL that you previously recorded:

   Name	Type	Value
   @	TXT	App-01.azurewebsites.net

Add a custom domain

Add a custom domain for both web apps.

1. Open your resource group and select your first web app.

2. In the left column, select Custom domains.

3. Under Custom Domains, select Add custom domain.

4. Under Custom domain, type your custom domain name. For example, contoso.com.

5. Select Validate.

   Your domain should pass validation and show green check marks next to Hostname availability and Domain ownership.

6. Select Add custom domain.

7. To see the new hostname under Hostnames assigned to site, refresh your browser. The refresh on the page doesn't always show changes right away.

8. Repeat this procedure for your second web app.

Add the alias record set

Now add an alias record for the zone apex.

1. Open your resource group and select the DNS zone.

2. Select Record set.

3. Add the record set using the following table:

   Name	Type	Alias record set	Alias type	Azure resource
   @	A	Yes	Azure resource	Traffic Manager - your profile

Test your web apps

Now you can test to make sure you can reach your web app and that it's being load balanced.

1. Open a web browser and browse to your domain. For example, contoso.com. You should see the default web app page.
2. Stop your first web app.
3. Close your web browser, and wait a few minutes.
4. Start your web browser and browse to your domain. You should still see the default web app page.
5. Stop your second web app.
6. Close your web browser, and wait a few minutes.
7. Start your web browser and browse to your domain. You should see Error 403, indicating that the web app is stopped.
8. Start your second web app.
9. Close your web browser, and wait a few minutes.
10. Start your web browser and browse to your domain. You should see the default web app page again.