Windows IIS website, which is bound to approximately 70 hostnames, want to configure the APPGW for the website

Question

Hi All,

We have a Windows IIS website, which is bound to approximately 70 hostnames. We want to configure the website behind the Azure Application Gateway; could you please help in configuring the Listener and HTTP settings to handle around 70 hostnames?

Thanks & Regards,

Veera.

Answer 1

Hello @Veera ,

Welcome to Microsoft Q&A Platform. Thank you for reaching out & hope you are doing well.

I understand that you would like to create an Application gateway to handle 70 hostnames and would like to know how to configure the listener and HTTP settings for same.

As per Application gateway limits,

And each active multi-site listener can have 5 hostnames.

NOTE: The number of resources listed in the table applies to standard Application Gateway SKUs and WAF-enabled SKUs running CRS 3.2 or higher. For WAF-enabled SKUs running CRS 3.1 or lower, the supported number is 40.

Refer: https://learn.microsoft.com/en-us/azure/azure-resource-manager/management/azure-subscription-service-limits#application-gateway-limits

https://learn.microsoft.com/en-us/azure/application-gateway/application-gateway-faq#what-is-considered-an-active-listener-versus-an-inactive-listener

Application Gateway allows host-based routing using multi-site HTTP(S) listener. Multi-site hosting enables you to configure more than one web application on the same port of application gateways using public-facing listeners. It allows you to configure a more efficient topology for your deployments by adding up to 100+ websites to one application gateway. You can use wildcard characters like asterisk (*) and question mark (?) in the host name, and up to 5 host names per multi-site HTTP(S) listener.

Refer: https://learn.microsoft.com/en-us/azure/application-gateway/multiple-site-overview

The thing that you need to consider if and when using HTTPS is that - "if multiple host names are mentioned in the same listener, you must upload a SAN certificate (Subject Alternative Names) with the CNs matching the host names mentioned".

For example, a listener can contain contoso.com, fabrikam.com which accepts requests for both the host names.

When creating a listener, you should select the below options:

• Listener type: Multi-site
• Host type: Multiple/Wild card
• Hostnames: Add the hostnames of your sites (you can add 5 hostnames per listener)

If using HTTPS protocol, make sure that you are using SAN certificate (Subject Alternative Names) with the CNs matching the host names configured in each listener.

The Backend setting will determine the behavior of the routing rule. The port and protocol used in the HTTP settings determine whether the traffic between the application gateway and backend servers is encrypted (providing end-to-end TLS) or unencrypted.

So, when creating backend/HTTP setting for a listener, make sure you add the port and protocol on which the application will connect in the backend and then bind the listener and backend setting using a routing rule.

Refer: https://learn.microsoft.com/en-us/azure/application-gateway/create-multiple-sites-portal

Kindly let us know if the above helps or you need further assistance on this issue.

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