Application Gateway is not working

Hi @Purna Durgarao Sugandhapu,

Thank you for reaching out on the Microsoft Q&A forum.

Please try starting the Application Gateway using the Azure CLI command below:

az network application-gateway start -g <MyResourceGroup> -n <MyAppGateway>

Reference: https://learn.microsoft.com/en-us/cli/azure/network/application-gateway?view=azure-cli-latest#az-network-application-gateway-start

Next, verify the gateway state using Azure PowerShell or Azure CLI and confirm both OperationalState and ProvisioningState. An Application Gateway may fail to start if there are underlying configuration or dependency issues, such as invalid certificate references, deleted public IPs, or blocked management-plane traffic. These issues must be resolved before the gateway can successfully run. https://learn.microsoft.com/en-us/azure/application-gateway/application-gateway-faq

Additionally, please check for any expired or unused SSL certificates associated with listeners, backend HTTP settings, or Key Vault references, and remove or replace them if found, as expired certificates can prevent the Application Gateway from starting successfully.

Once the gateway starts successfully, you can validate traffic flow by checking Backend Health. If backend pools show Unhealthy or Unknown, review the health probe configuration, confirm the backend ports and paths are correct, and ensure that NSGs, UDRs, and DNS allow connectivity from the Application Gateway subnet to the backend servers. Application Gateway does not forward traffic when backend health is unhealthy or unknown, which is expected behavior. https://learn.microsoft.com/en-us/troubleshoot/azure/application-gateway/application-gateway-backend-health-troubleshooting

If the gateway still fails to start, please share the requested details via private message so we can investigate further.

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