[Documentation] Add How to configure an Azure Application Gateway

docs/_docs/help/known-issues.md

@@ -157,3 +157,18 @@ The workaround at this time is to run this ahead of any of the Virtual Assistant
 ```
 $env:PATH += ":/users/YOUR_USER_NAME/.dotnet/tools"
 ```
+
+## Configuring a Gateway's health probe with a TypeScript bot
+The TypeScript bot samples do not have a welcome page, therefore when the gateway tries to check its backend pool's health will result in an error 404 causing the health validation to fail, which in turn will cause an error 502 when trying to access the resource through the public IP.
+
+To workaround this:
+1. In the Azure portal, select your application gateway.
+1. Under **Health Probes**, select to add a new one
+1. Enter a name for your probe, such as *MyHealthProbe*
+1. In **Protocol**, select *HTTP*
+1. In **Host** enter your resource host, it has to be the same host you selected as target in the backend pool
+1. In **Path** enter `/api/messages`, to validate the response of the bot
+1. In **HTTP response status code match**, enter *405* which is the expected response for the TypeScript Virtual Assistant bot
+1. Finally, test and save the configuration
+
+![help_known_issues_gateway_typescript]({{site.baseurl}}/assets/images/help_known_issues_gateway_typescript.jpg)

docs/_docs/virtual-assistant/handbook/configure-an-azure-application-gateway.md

@@ -0,0 +1,41 @@
+---
+category: Virtual Assistant
+subcategory: Handbook
+title: Configure an Azure Application Gateway
+description: This explains how to configure and use a bot sample through the public IP of an Azure Application Gateway.
+order: 14
+toc: true
+---
+
+# {{ page.title }}
+{:.no_toc}
+{{ page.description }}
+
+## Prerequisites
+
+-  Have a deployed [Virtual Assistant]({{site.baseurl}}/overview/virtual-assistant-solution/)
+-  The [BotFramework Emulator](https://github.com/microsoft/BotFramework-Emulator)
+
+## Create an Azure Application Gateway
+
+Follow the document [Tutorial: Create an application gateway with a Web Application Firewall using the Azure portal](https://docs.microsoft.com/en-us/azure/web-application-firewall/ag/application-gateway-web-application-firewall-portal) up to *Review + create tab* section.
+
+You should end up with the following resources in your Azure resource group:
+
+![]({{site.baseurl}}/assets/images/virtualassistant-gateway-resources.png)
+
+## Configure the Gateway's backend pool
+
+Now it is necessary to link your deployed bot to the backend pool of your application gateway. For this follow the steps detailed in [Add App service as backend pool](https://docs.microsoft.com/en-us/azure/application-gateway/configure-web-app-portal#add-app-service-as-backend-pool) and in [Edit HTTP settings for App Service](https://docs.microsoft.com/en-us/azure/application-gateway/configure-web-app-portal#edit-http-settings-for-app-service).
+
+> If you are using a TypeScript bot sample, check [How to configure a TypeScript bot with an Application Gateway]({{site.baseurl}}/help/known-issues#configuring-a-gateway's-health-probe-with-a-typescript-bot).
+
+After overriding the hostname, you can use the gateway's public IP to access your bot.
+
+![]({{site.baseurl}}/assets/images/virtualassistant-gateway-emulator.png)
+
+## Further Reading
+
+- [Deploying a Virtual Assistant](https://microsoft.github.io/botframework-solutions/virtual-assistant/tutorials/deploy-assistant/cli/1-intro/)
+- [Troubleshoot backend health issues in Application Gateway](https://docs.microsoft.com/en-us/azure/application-gateway/application-gateway-backend-health-troubleshooting)
+- [Troubleshooting bad gateway errors in Application Gateway](https://docs.microsoft.com/en-us/azure/application-gateway/application-gateway-troubleshooting-502)