Azure Application Gateway
An Azure service that provides a platform-managed, scalable, and highly available application delivery controller as a service.
1,072 questions
How to point to virtual machine configured in application gateway backend pool
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Neerav Agrawal
45
Reputation points
I have setup an application gateway to point one app service and one virtual machince through it.
I have DNS configurations (CNAME) set-up for both based upon respective custom domains. For example
- From DNS configuration "appservice.service.com" domain is pointing to application gateway, and that is correctly pointing to its app service configured in first backend pool of application gateway. Because same domain is added as a custom domain in app service.
- From DNS configuration "virtualmachine.service.com" domain is pointing to application gateway. In application gateway the second backend pool is configured for virtual machine but it is not pointing here correctly. I think it is not identifying it.
Can anyone please suggest how to resolve this.
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ChaitanyaNaykodi-MSFT 26,111 Reputation points Microsoft Employee2023-09-21T23:56:39.06+00:00 Thank you for reaching out.
It seems like you are facing an issue with your Azure Application Gateway configuration.
To help troubleshoot this issue, can you check backend health status as shown here for the VM backend pool?
If the backend health status is unhealthy, you can follow the DNS resolution steps as mentioned here notably.
- Verify that the FQDN entered in the backend pool is correct and that it's a public domain, then try to resolve it from your local machine.
- If the domain is private or internal, try to resolve it from a VM in the same virtual network. If you can resolve it, restart Application Gateway and check again
Hope this helps! Thank you!
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ChaitanyaNaykodi-MSFT 26,111 Reputation points Microsoft Employee
2023-09-23T00:00:33.0133333+00:00 Just following up here to see if you were able take a look at my comment above. Thank you!
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Neerav Agrawal 45 Reputation points
2023-09-25T20:00:49.9766667+00:00 Thanks for the response and solution. Please see below more details of implementation I have done.
DNS entry:
subdomainvm.domain.com -> A record -> IP (application gateway)subdomainapp.domain.com -> CNAME -> DNS name (application gateway)
Application Gateway:
Backend pool ->
- Target type (app service) -> app service (in this app service the custom domain has been configured with the sub domain subdomainapp.domain.com) - This is working perfectly fine.
- Target type (virtual machine) -> virtual machine - This is not resolving. The main point is how the sub domain (subdomainvm.domain.com) configured in DNS records would understand this mapping and point to its respective VM? This VM don't have any custom domain configuration.
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ChaitanyaNaykodi-MSFT 26,111 Reputation points Microsoft Employee
2023-09-28T00:01:07.6066667+00:00 Thank you for getting back.
Just to clarify my understanding, can you please share where you have defined the A record DNS entry for subdomainvm.domain.com? and also have you registered the domain with a Domain registrar?
Just FYI, you can't use Azure DNS to buy a domain name. For an annual fee, you can buy a domain name by using App Service domains or a third-party domain name registrar. Your domains then can be hosted in Azure DNS for record management. For more information, see Delegate a domain to Azure DNS.
If you have already registered the domain with a domain registrar, can you please do a NSLookup command for subdomainvm.domain.com and see if it is resolving to the Application gateway's IP?
You can enter this command in local machine's command prompt
nslookup subdomainvm.domain.comYou can go through this doc to understand how to add VM's to the backend pool of a Application Gateway and this documentation to understand how Application Gateway routes request to the backend pool to after the DNS resolution is succesful.
Thank you! Looking forward to your reply.
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Neerav Agrawal 45 Reputation points
2023-09-28T02:10:29.3433333+00:00 The domains I mentioned here are for example only. I have actual subdomains which are already registered in DNS records with domain registrar only.
The configurations are done as I mentioned in earlier comments. The issue is that the VM domain is also pointing the pool set-up for app service. I think it is not pointing to it correctly.
Can we connect on screen share on teams tomorrow?
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ChaitanyaNaykodi-MSFT 26,111 Reputation points Microsoft Employee
2023-09-29T02:54:19.3033333+00:00 Sure, could you please send an email to azcommunity@microsoft.com with the below details.
Subject : Attn Chaitanya
Thread URL: Link to this thread.
Subscription ID
Please let me know once you have done the same.
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Neerav Agrawal 45 Reputation points
2023-09-29T15:31:47.92+00:00 Done.
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ChaitanyaNaykodi-MSFT 26,111 Reputation points Microsoft Employee
2023-09-30T05:04:51.1433333+00:00 Thank you for getting back. I have replied to your email.
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