Runbook: Application Gateway Backend Unhealthy

Purpose

Use this runbook when Application Gateway reports unhealthy backend pool members.

Checks

1. Open Application Gateway backend health.
2. Identify unhealthy backend targets.
3. Review probe configuration.
4. Confirm backend service is listening on the expected port.
5. Check NSG and route table changes.
6. Confirm certificates if HTTPS probing is used.
7. Review recent deployments or firewall changes.

Resolution Options

• Restart backend service where approved
• Correct probe path or port if misconfigured
• Escalate network changes if routing or NSG rules are blocking traffic
• Escalate to Application Support if the service is not responding correctly