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Configure Traffic Manager and Web Apps over SSL (HTTPS) using custom domain

In this topic we will cover what we shall do when we:
  • Configure Azure Traffic Manager on top of Web Applications hosted inside App Services 
  • Over HTTPS
  • With custom domain 
  • Client certificates
Context
When we are using HTTPS in combination with App Services, everything will go smooth. You just need to activate the HTTPS and upload client certificate, if you want to use a custom one.
Things are a little different when you want to configure HTTPS on top of Traffic Manager. In theory, the steps are clear and it should work as expected, but combined this with custom domain and client certificates things can end up with a 404 error code..

Initial Setup
Pre requirements: Web Apps are configured over SSL using custom domain and works as expected.
Let’s take a look on the base steps that needs to be done when you want such a configuration

  • Create an instance of Traffic Manager inside Azure Portal and add your Web Apps that you already configured for HTTPS
  • Add your custom domain to your DNS Record – this step is done in the tool provided by the company from where you bought the domain (you will need to add the Traffic Manager domain name
  • Wait for DNS change to propagete
  • Inside each Web App add to Custom Domains the CNAME that you want (e.g. www.rv.com)

We are done! You now need to access your application.

Surprise – 404
When you try to access your custom domain over SSL you get a 404 error code. If we look on the logs on each web application, we will not be able to find any 404 errors. The only thing that we could see would be the health check on each web site, that are done by traffic manager.
Let us analyze the problem. Traffic Manager is just a DNS proxy (level 3). This means that he does not handle any request, just making the right redirection. Traffic Manager will never return an error code like this, because is just a DNS proxy.
This means that error code comes from our web application. However, 404 is strange, especially if we cannot find any logs related to it. Inside Kudu, we will not be able to see any requests that are coming to our web application. This means only one things – the error code is appearing during the handshake of SSL.

Cause
We have configured the list of custom domain inside our web application to contain the one that we want to use. Automatically, Traffic Manager added his domain name inside each web application.
Nevertheless, for Traffic Manager you configured a custom sub domain that was not added in each Web Application.

Solution
You need to add the custom CNAME of your traffic manager inside each Web Application or you can use a SSL certificate without alternatives names. I usually prefer the first options, because I have better control. Not all the time I can control a certificate that was generated by a 3rd party.

Conclusion
This is that kind of configuration that you forget about it in one week, but each time you will lose a few hours to find the root cause.

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