Link port to DNS name in Azure VM

JN 0

Hi,

I have an Azure VM with DNS name of testing.southeastasia.cloudapp.azure.com which links to IP address of 52.157.189.61. How can I instead make it so that the DNS name links to a specific port in that IP address i.e. 52.157.189.61:8501?

Thanks

Richard 6 Reputation points

2024-03-19T13:51:17.3+00:00

DNS provides a SRV (service) record that allows you to specify the port (as well as the IP address) resolution for your domain, see: https://learn.microsoft.com/en-us/azure/dns/dns-zones-records
Jackson Martins 9,646 Reputation points MVP

2024-03-19T13:56:06.4266667+00:00

@Richard

I believe you are confused, DNS does not do port redirection, you would need another application to work at this layer, such as Firewall, Reverse Proxy and Web Server.

DNS will only provide name-to-IP resolution
JN 0 Reputation points

2024-03-19T14:17:25.3933333+00:00

Can you expand on how I can use the SRV?
Richard 6 Reputation points

2024-03-19T14:20:20.5266667+00:00

In its purest sense DNS is only name to IP resolution, most cloud providers have DNS that supports both an "A" record and "SRV" record - and real world example where these two records work in tandem and provides an answer to the question.

myservice.somewhere.com. 86400 IN A aaa.bbb.ccc.ddd

_myservice._tcp.somewhere.com. 86400 IN SRV 10 20 25125 myservice.somewhere.com. (redirects to port 25125)
Jackson Martins 9,646 Reputation points MVP

2024-03-19T14:23:00.54+00:00

SRV records will not redirect web traffic to different ports, normally you would use one of the previously mentioned methods, such as configuring a web server for redirection or using a reverse proxy, to achieve your goal for web services

For non-web services that support SRV records, defining an SRV record may be the correct approach. However, for general web traffic, you will need to employ one of the other strategies discussed.
Jackson Martins 9,646 Reputation points MVP

2024-03-19T14:25:30.5266667+00:00

SRV records are mainly used in specific scenarios where clients are designed to search these records. This is common in services such as SIP (for VoIP), XMPP (for instant messaging), and some email services, where client software can query DNS for SRV records to discover the current hostname and port on the which service is running.
KapilAnanth-MSFT 35,086 Reputation points Microsoft Employee

2024-03-21T11:28:06.72+00:00

@JN ,

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

I see Jackson Martins has addressed your queries.

Please let us know if we can be of any further assistance here.

Thanks,

Kapil

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1 answer

Jackson Martins 9,646 Reputation points MVP

2024-03-19T13:49:48.7633333+00:00

Hi JN

To make your DNS name test.southeasia.cloudapp.azure.com point to a specific port (such as 8501) in your IP address, you will need to understand that DNS itself cannot directly associate domain names with ports. DNS was designed to resolve domain names to IP addresses. However, there are several approaches you can take to achieve the behavior you are looking for.

You can configure a web server (like Nginx or Apache) to Reverse Proxy your VM to listen on the default HTTP (80) or HTTPS (443) port. This server can then redirect requests to your application running on a different port. For example, you can configure Nginx to redirect requests to 52.157.189.61:8501.

https://learn.microsoft.com/pt-br/azure/partner-solutions/nginx/nginx-overview

Azure Application Gateway or a Load Balancer can be used to route traffic arriving at a given DNS name (or IP) to any port you define. You would configure the DNS name to point to the Application Gateway or Load Balancer, and then configure rules within those services to route traffic to your application on the desired port.
https://learn.microsoft.com/en-us/azure/application-gateway/quick-create-portal

You can use Azure Firewall or another NSV to redirect traffic through the port, coming in on port 80 or 443 and redirecting to port 8501

https://learn.microsoft.com/en-us/azure/firewall/tutorial-firewall-deploy-portal

Get in touch if you need more help with this issue.

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JN 0 Reputation points

2024-03-19T14:37:56.1833333+00:00

I tried following the tutorial for the Application Gateway but am unsure in which part do I add the port that I want? i.e. 8501?

Is it this part?
"For the Backend setting, select Add new to add a new Backend setting. The Backend setting determines the behavior of the routing rule. In the Add Backend setting window that opens, enter myBackendSetting for the Backend settings name and 80 for the Backend port."

Jackson Martins 9,646 Reputation points MVP

2024-03-19T14:41:05.2366667+00:00

Yes, you are on the right path. When configuring Azure Application Gateway, you'll specify the port you want to use in the backend settings.

When you add a new backend configuration, the backend port you specify must be the port your application is actually listening on. If your application is listening on port 8501, you must enter 8501 for the Backend port instead of 80
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