Fix 403 Forbidden Error on Microsoft Azure Application Gateway v2: A Comprehensive Guide

This comprehensive guide will help you resolve the 403 Forbidden Error encountered while using Microsoft Azure Application Gateway v2. By following the step-by-step instructions provided in this guide, you'll be able to identify the root cause of the error and apply the necessary fixes.

Microsoft Azure Application Gateway is a web traffic load balancer that enables you to manage traffic to your web applications. The v2 SKU offers additional features such as autoscaling, zone redundancy, and Static VIP.

Table of Contents


Before you begin, ensure that you have the following:

  1. An active Azure subscription.
  2. Access to a configured Azure Application Gateway v2.
  3. Familiarity with Azure portal, Application Gateway, and basic networking concepts.

Step 1: Verify Backend Health

Check Backend Health Status

The first step in troubleshooting the 403 Forbidden Error is to verify the health of your backend servers. To do this, follow these steps:

  1. Sign in to the Azure portal.
  2. Navigate to your Application Gateway resource.
  3. Click on the "Backend health" tab.
  4. Check the health status of your backend pool members.

If the health status is "Healthy," proceed to the next step. If it's "Unhealthy," investigate the backend servers and resolve any issues found.

Validate Backend Server Response

Ensure that your backend servers are responding correctly to requests. You can use tools like Postman or curl to send test requests and validate the response.

Step 2: Check Custom Health Probes

Azure Application Gateway uses health probes to monitor the health of backend servers. The default probe settings may not suit all applications, so you can create custom health probes to match your application's requirements.

If you're using custom health probes, verify that they're configured correctly. Ensure that the probe's URL, interval, and timeout settings are appropriate for your application. You can refer to Azure's documentation on health probes for more information.

Step 3: Inspect Listener Configuration

A misconfigured listener can cause a 403 Forbidden Error. Ensure that your listener is configured correctly by following these steps:

  1. Sign in to the Azure portal.
  2. Navigate to your Application Gateway resource.
  3. Click on the "Listeners" tab.
  4. Inspect the listener configuration, including the protocol, port, and SSL certificate (if applicable).

Ensure that the listener is associated with the correct backend pool and HTTP settings. If necessary, make changes to the listener configuration and save them.

Step 4: Review Backend Authentication

The Application Gateway can authenticate with the backend server using client certificates. If you're using this feature, verify that the client certificates are configured correctly and have not expired.

You can review the backend authentication settings by navigating to your Application Gateway resource, clicking on the "HTTP settings" tab, and inspecting the "Authentication certificates" section.

Step 5: Analyze Application Gateway Logs

Azure Application Gateway provides access logs, performance logs, and firewall logs that can help you identify the cause of the 403 Forbidden Error. You can enable and configure logging by following Azure's documentation.

Once logging is enabled, analyze the logs to identify any issues with the Application Gateway configuration, backend servers, or client requests.


1. What is a 403 Forbidden Error?

A 403 Forbidden Error occurs when the server understands the request but refuses to authorize it. This status is returned when the server does not have the necessary permissions to access the requested resource.

2. Can I use custom error pages for 403 Forbidden Errors?

Yes, you can configure custom error pages for 403 Forbidden Errors in Azure Application Gateway. Follow Azure's documentation on custom error pages to set up custom error pages for your application.

3. How do I enable autoscaling for my Application Gateway v2?

Autoscaling is enabled by default when you create an Application Gateway v2. You can configure the minimum and maximum instance count by following Azure's documentation on autoscaling.

4. Can I use Azure Application Gateway with Web Application Firewall (WAF)?

Yes, you can use Azure Application Gateway with Web Application Firewall (WAF) to protect your web applications from common web vulnerabilities. Follow Azure's documentation on WAF to set up WAF for your application.

5. How do I monitor the performance of my Application Gateway?

You can monitor the performance of your Application Gateway using Azure Monitor, which provides access to performance metrics, alerts, and logs. Refer to Azure's documentation on monitoring for more information.

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