# Test each hostname-to-backend mapping on a multi-site Application Gateway

> Verify routing identity when several websites share the gateway.

- Canonical URL: https://update.dsesecurity.com/updates/dse-20260917-162-test-each-hostname-to-backend-mapping-on-a-multi-site-application-gateway/
- Publisher: Detection Systems & Engineering (DSE Security)
- Author: DSE Security Editorial Team
- Published: 2026-09-17T16:32:18+00:00
- Modified: 2026-09-17T16:46:29+00:00
- Last reviewed by DSE: 2026-09-17
- Resource type: Guide
- DSE priority: Information
- Topics: Cybersecurity, Networks & Infrastructure
- Reading time: 2 minutes

## What you need to know

Verify routing identity when several websites share the gateway.

## Potentially affected

Apply this review to a gateway serving multiple approved hostnames. Identify the real listeners, routing rules, backend settings and pools. Use the current platform requirements for the actual deployment; this article does not prescribe the tutorial's example operating system or public-access configuration.

## DSE recommendation

DSE recommends a hostname mapping table owned jointly by the application and gateway teams.

## Article

## Source facts

Microsoft’s multi-site Application Gateway tutorial defines separate backend pools and configures listeners and routing rules around two domain names. The stated purpose is to direct each website’s requests to the appropriate servers. The tutorial’s example domains and virtual machines illustrate the mapping rather than identifying an organization’s production resources. [Microsoft Learn](https://learn.microsoft.com/en-us/azure/application-gateway/create-multiple-sites-portal).

## Applicability

Apply this review to a gateway serving multiple approved hostnames. Identify the real listeners, routing rules, backend settings and pools. Use the current platform requirements for the actual deployment; this article does not prescribe the tutorial’s example operating system or public-access configuration.

## DSE recommendation

DSE recommends a hostname mapping table owned jointly by the application and gateway teams. Record the expected backend and response for every site, plus the intended handling of an unknown hostname. Review changes that reuse an existing listener or backend setting against all affected sites. Preserve the old mapping and an approved restoration sequence.

## Verification

From an authorized client, send a representative request for each configured hostname and correlate it with backend-side observations. Confirm the content and application behavior as well as the destination pool. Test the agreed unknown-host case. Repeat all relevant mappings after a listener or rule change so a working first website does not conceal an incorrect second-site route.

## Official references

[Microsoft Learn: Tutorial: Create and configure an application gateway to host multiple web sites using the Azure portal](https://learn.microsoft.com/en-us/azure/application-gateway/create-multiple-sites-portal).

## Primary reference

- Name: Tutorial: Create and configure an application gateway to host multiple web sites using the Azure portal - Azure Application Gateway | Microsoft Learn
- Authority: Microsoft Learn
- URL: https://learn.microsoft.com/en-us/azure/application-gateway/create-multiple-sites-portal
- Source publication date: Not stated by the source

## Citation and use

Preferred citation: “Test each hostname-to-backend mapping on a multi-site Application Gateway,” DSE Security, https://update.dsesecurity.com/updates/dse-20260917-162-test-each-hostname-to-backend-mapping-on-a-multi-site-application-gateway/
Publishing principles: https://update.dsesecurity.com/updates/dse-updates-editorial-methodology/
Usage and citation policy: https://update.dsesecurity.com/usage/
Copyright © 2026 Detection Systems & Engineering. All rights reserved.