Azure Load Balancer Won't Pass Traffic to VM

Chase Schwab 0

I’m setting up an Azure server which hosts two applications.

One of them is an AV console that needs all external endpoint IPs to hit a nonstandard port on the server. The other is a backup console which needs specific static IPs to hit a number of ports on the server.

Currently I have a load balancer with NAT rules translating the traffic to the VM. I have network rules on the VM allowing the traffic.

AV Example: Load balancer w/ static IP has NAT rule of ANY traffic on port 22222 directed to VM1. VM1 has a network rule of “allow” ANY traffic on port 22222. This is because endpoints are roaming.

Backup Example: Load balancer w/ static IP has NAT rule of ANY traffic on port 6789 directed to VM1. VM1 has a network rule of “allow” traffic on port 6789 from IPs x.x.x.x, x.x.x.x., etc.

Still, none of the traffic passes through. Both services are disconnected from endpoints as well as explicit port checks failing.

What am I missing? Is there a rule I need for the load balancer to pass the traffic directly to the VM? Is there a basic setting I have disabled maybe?

Sina Salam 10,646 Reputation points

2024-07-31T20:52:12.4533333+00:00
Hello Chase Schwab,

Welcome to the Microsoft Q&A and thank you for posting your questions here.

Problem

I understand that in your Azure Load Balancer configuration, traffic is not passing through as expected.

Solution

Regarding your explanations, it looks like you've set up the NAT rules and network rules correctly, but the traffic isn't passing through as expected. Something is missing somewhere, and I will provide below few areas you will need to check:

Start by using tools like telnet or nc to test connectivity from external endpoints to the load balancer's public IP on the specified ports. affirm that the load balancer is forwarding traffic to VM1.

Check if the backend pool configuration includes the correct VMs by ensuring that your VM (VM1) is correctly added to the backend pool of the load balancer. Verify that VM1 is healthy and responsive.

Confirm that health probes are configured properly. Health probes determine whether a VM is healthy and should receive traffic. Verify that the health probe settings match the expected behavior of your applications.

Review the NSG rules associated with your VM. Make sure there are no conflicting rules that might block the traffic. Also, check both inbound and outbound rules in the NSG.

If your applications require outbound traffic (e.g., connecting to external services), ensure that outbound rules are correctly configured. Also, consider disabling automatic outbound NAT if you need more control over outbound traffic.

If you're using a public IP address, verify that it's correctly associated with the load balancer and the frontend configuration. You will need to check if the public IP is correctly mapped to the load balancer's frontend.

Double-check the NAT rules in the load balancer configuration. Ensure that the port mappings are correct and verify that the frontend port (external port) matches the expected port (e.g., 22222 or 6789).

Lastly, enable diagnostic logs for the load balancer and VMs. Review the logs to identify any issues and monitor metrics related to the load balancer, backend pool, and VMs to detect anomalies for more information.

Accept Answer

I hope this is helpful! Do not hesitate to let me know if you have any other questions.

** Please don't forget to close up the thread here by upvoting and accept it as an answer if it is helpful ** so that others in the community facing similar issues can easily find the solution.

Best Regards,

Sina Salam

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