---
title: Azure Application Gateway Healthy Hosts | Blue Matador - Troubleshooting
description: Blue Matador detects when the hosts backing your Azure Application Gateway are unhealthy.
image: https://www.bluematador.com/hubfs/logo-1.png
---

 Docs

# Azure Application Gateway Healthy Hosts

Azure Application Gateway is configured to send traffic to Backend Pools. When those pools contain fewer healthy VMs than expected, the application gateway is considered unhealthy. When this happens, the remaining VMs will handle the full amount of requests, which can quickly overwhelm your application. Blue Matador watches the **UnhealthyHostCount** metric and creates events when there are unhealthy hosts in your application gateway.

## Effects

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- Increased load on other VMs backing the application gateway
- Cascading failures as other VMs are unable to keep up with the load to the application gateway

## Fixes

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To troubleshoot unhealthy hosts try the following:

- Check the health probe endpoint for errors
- Check general host health. Look at application logs, server metrics, or APM metrics to determine what is making your VM unhealthy.
- Use [autoscaling](https://docs.microsoft.com/en-us/azure/application-gateway/application-gateway-autoscaling-zone-redundant) with your application gateway to ensure that you always have enough servers to handle load

## Resources

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- [Supported metrics for Application Gateway](https://docs.microsoft.com/en-us/azure/azure-monitor/platform/metrics-supported#microsoftnetworkapplicationgateways) (Microsoft Azure Documentation)
- [Application Gateway health monitoring overview](https://docs.microsoft.com/en-us/azure/application-gateway/application-gateway-probe-overview) (Microsoft Azure Documentation)
- [Back-end health, diagnostic logs, and metrics for Application Gateway](https://docs.microsoft.com/en-us/azure/application-gateway/application-gateway-diagnostics) (Microsoft Azure Documentation)
- [Autoscaling and Zone-redundant Application Gateway v2](https://docs.microsoft.com/en-us/azure/application-gateway/application-gateway-autoscaling-zone-redundant) (Microsoft Azure Documentation)