Resolving Azure Application Gateway Backend Health Issues

Question

How can I troubleshoot and resolve issues with unhealthy or unknown backends in my Azure Application Gateway?

PS - Based on common issues that we have seen from customers and other sources; we are posting these questions to help the Azure community.

Answer 1

To troubleshoot and resolve issues with unhealthy or unknown backends in your Azure Application Gateway, follow these steps:

1. Check Backend Health Status:
   • Navigate to the Azure portal, go to your Application Gateway, and check the backend health status. This can be found under "Backend Health" in the monitoring section.
2. Verify Backend Configuration:
   • Ensure that the backend pool is correctly configured with the right IP addresses or FQDNs.
   • Check that the backend servers are running and reachable.
3. Examine Health Probes:
   • Health probes are used to determine the health status of your backends. Verify that the health probes are correctly configured.
   • Ensure the probe settings (protocol, path, interval, timeout) match the configuration of your backend application.
4. Review Network Security:
   • Ensure that network security groups (NSGs) and firewalls are not blocking traffic between the Application Gateway and the backend servers.
   • Check for any IP restrictions on your backend servers that might prevent the Application Gateway from accessing them.
5. Analyze Logs:
   • Check the diagnostic logs for any errors or warnings that can provide clues about the issue.
   • Enable and review the Application Gateway access logs, performance logs, and firewall logs if not already enabled.
6. Backend Server Health:
   • Ensure the backend servers are healthy and not experiencing high CPU, memory usage, or other resource constraints.
   • Look for application-specific issues that might be causing the backend to be unhealthy.
7. SSL/TLS Configuration:
   • If you are using HTTPS, ensure that the SSL/TLS certificates are correctly configured and not expired.
   • Verify that the SSL settings on the Application Gateway match those on the backend servers.

For further details, refer to the official Azure documentation:

• Troubleshoot backend health issues in Application Gateway
• Azure Application Gateway diagnostics and logging

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