All the instances in one or more of your backend pools are unhealthy. This will result in a 502 error when you try to access your application hosted behind the Application Gateway. Please check the backend health and resolve the issue.

Question

All the instances in one or more of your backend pools are unhealthy. This will result in a 502 error when you try to access your application hosted behind the Application Gateway. Please check the backend health and resolve the issue.

Answer 1

@Jayapal Reddy Tholeti

Thank you for reaching out.

I understand you are facing backend health issues for one of the backend servers of your Application Gateway.

By default, Azure Application Gateway probes backend servers to check their health status and to check whether they're ready to serve requests. Users can also create custom probes to mention the host name, the path to be probed, and the status codes to be accepted as Healthy. In each case, if the backend server doesn't respond successfully, Application Gateway marks the server as Unhealthy and stops forwarding requests to the server. After the server starts responding successfully, Application Gateway resumes forwarding the requests.

You can follow the troubleshooting guide here to check the backend health and take appropriate actions.

Thank you!