Load balancer status is Degraded (Unplanned)

Hi Anuja Ambekar,

Welcome to Microsoft Q&A and thank you for posting your query here!

When your Azure Load Balancer health status shows as Degraded (Unplanned) and you notice issues such as the service on the VM running but the GUI portal connected to it not accessible by hostname (while IP access still works), it indicates a health or routing issue affecting the load balancer’s backend pool or network path.

Here is a detailed step-by-step approach to troubleshoot and address this issue based on Microsoft documentation:

Step 1: Understand Degraded Status

• A Degraded load balancer typically means the Data Path Availability is between 25% and 90%, indicating some backend endpoints may be unhealthy or unreachable.
• This condition can result in dropped requests or partial unavailability of applications routed through the load balancer.

Step 2: Verify Backend Health Probes and VM Status

• Check the Health Probe Status on your load balancer to see whether backend VMs are responding as expected.
• Even if VMs are up and services running, health probes failing to respond or timing out will cause the load balancer to mark that instance as unhealthy.
• Confirm the probe endpoint (port and path) is reachable and healthy.
• Reference: Manage Azure Load Balancer health status.​

Step 3: Analyze Frontend and Backend Availability Metrics

• Use Azure portal metrics for your load balancer to review frontend and backend availability over the last 30 minutes to identify when degradation began.
• If Data Path Availability is low or 0%, it confirms a routing or backend availability issue.

Step 4: Investigate Hostname vs IP Access Issue

• When you can access the VM service via IP but not hostname, it often indicates a DNS or hostname resolution problem rather than a load balancer issue.
• Verify the hostname is correctly resolved to the load balancer’s frontend IP via DNS, and no DNS misconfiguration or caching is causing failures.
• Also, ensure hostname-based routing rules or network security groups are not blocking access.
• For internal load balancers, note that accessing the load balancer IP from the backend VM itself may not be supported due to SNAT restrictions.

Step 5: Run Load Balancer Diagnostics and Automated Troubleshooter

• Use the Diagnose and solve problems blade in the Azure portal on your load balancer resource to automatically identify common issues.
• Collect diagnostic logs and network captures (e.g., PsPing) from backend VMs to validate probe connectivity.

Step 6: Check for Recent Platform or Azure Service Issues

• Rarely, issues in Azure platform can cause load balancer degradation. Check Azure Service Health for any ongoing incidents.
• Reference: Azure status page.​

i hope the response helps, please do let me know if you have any questions on this.

Thanks,

Harish,