Common Issues and Solutions for Azure Load Balancer

1. Backend Instances Not Responding to Health Probes:

- Issue: Backend instances are marked as unhealthy and not responding to health probes, which may cause data path unavailability.

- Solution:

- Verify that the VM instances are listening on the correct probe ports.

- Ensure Network Security Group (NSG) rules allow Azure Load Balancer traffic.

- Check that the application running on the instances is healthy by accessing it via the private or public IP.

2. SNAT Port Exhaustion:

- Issue: Exhaustion of SNAT ports when outbound connections are initiated frequently, leading to connection failures.

- Solution:

- Use a NAT Gateway to manage SNAT allocation more efficiently.

- Add additional public IP addresses to increase the number of available SNAT ports.

3. Misconfigured Health Probe:

- Issue: Health probes fail due to misconfiguration, such as incorrect port, protocol, or probe type.

- Solution:

- Verify that the probe is configured with the correct protocol and port.

- Ensure the application responds with a 200 OK status for HTTP/HTTPS probes.

4. Intermittent Connection Timeouts:

- Issue: Internal load balancer (ILB) connections may time out intermittently if traffic is directed back to the originating VM.

- Solution:

- Consider using a proxy layer behind the internal load balancer or implement Direct Server Return (DSR) style rules to mitigate this issue.

5. High CPU Utilization:

- Issue: High CPU usage on backend resources, potentially affecting the load balancer's health probe status.

- Solution:

- Monitor and optimize CPU usage via Azure Monitor to ensure backend instances are not overloaded.

These solutions address common configuration and performance challenges when using Azure Load Balancer