Merge pull request #202182 from JasonFreeberg/patch-115

Add doc section for Debian 11 rollout

Author: v-regandowner

articles/app-service/overview.md

@@ -40,14 +40,54 @@ App Service can also host web apps natively on Linux for supported application s
 
 ### Built-in languages and frameworks
 
-App Service on Linux supports a number of language specific built-in images. Just deploy your code. Supported languages include: Node.js, Java (JRE 8 & JRE 11), PHP, Python, .NET Core, and Ruby. Run [`az webapp list-runtimes --os linux`](/cli/azure/webapp#az-webapp-list-runtimes) to view the latest languages and supported versions. If the runtime your application requires is not supported in the built-in images, you can deploy it with a custom container.
+App Service on Linux supports a number of language specific built-in images. Just deploy your code. Supported languages include: Node.js, Java (8, 11, and 17), Tomcat, PHP, Python, .NET Core, and Ruby. Run [`az webapp list-runtimes --os linux`](/cli/azure/webapp#az-webapp-list-runtimes) to view the latest languages and supported versions. If the runtime your application requires is not supported in the built-in images, you can deploy it with a custom container.
 
 Outdated runtimes are periodically removed from the Web Apps Create and Configuration blades in the Portal. These runtimes are hidden from the Portal when they are deprecated by the maintaining organization or found to have significant vulnerabilities. These options are hidden to guide customers to the latest runtimes where they will be the most successful.
 
 When an outdated runtime is hidden from the Portal, any of your existing sites using that version will continue to run. If a runtime is fully removed from the App Service platform, your Azure subscription owner(s) will receive an email notice before the removal.
 
 If you need to create another web app with an outdated runtime version that is no longer shown on the Portal see the language configuration guides for instructions on how to get the runtime version of your site. You can use the Azure CLI to create another site with the same runtime. Alternatively, you can use the **Export Template** button on the web app blade in the Portal to export an ARM template of the site. You can reuse this template to deploy a new site with the same runtime and configuration.
 
+#### Debian 9 End of Life
+
+On June 30th 2022 Debian 9 (also known as "Stretch") will reach End-of-Life (EOL) status, which means security patches and updates will cease. As of June 2022, a platform update is rolling out to provide an upgrade path to Debian 11 (also known as "Bullseye"). The runtimes listed below are currently using Debian 9; if you are using one of the listed runtimes, follow the instructions below to upgrade your site to Bullseye.
+
+- Python 3.8
+- Python 3.7
+- .NET 3.1
+- PHP 7.4
+
+> [!NOTE]
+> To ensure customer applications are running on secure and supported Debian distributions, after February 2023 all Linux web apps still running on Debian 9 (Stretch) will be upgraded to Debian 11 (Bullseye) automatically.
+>
+
+##### Verify the platform update
+
+First, validate that the new platform update which contains Debian 11 has reached your site.
+
+1. Navigate to the SCM site (also known as Kudu site) of your webapp. You can browse to this site at `http://<your-site-name>.scm.azurewebsites.net/Env` (replace `\<your-site-name>` with the name of your web app).
+1. Under "Environment Variables", search for `PLATFORM_VERSION`. The value of this environment variable is the current platform version of your web app. 
+1. If the value of `PLATFORM_VERSION` starts with "99" or greater, then your site is on the latest platform update and you can continue to the section below. If the value does **not** show "99" or greater, then your site has not yet received the latest platform update--please check again at a later date.
+
+Next, create a deployment slot to test that your application works properly with Debian 11 before applying the change to production.
+
+1. [Create a deployment slot](deploy-staging-slots.md#add-a-slot) if you do not already have one, and clone your settings from the production slot. A deployment slot will allow you to safely test changes to your application (such as upgrading to Debian 11) and swap those changes into production after review. 
+1. To upgrade to Debian 11 (Bullseye), create an app setting on your slot named `APPSETTING_DEFAULT_OS` with a value of `bullseye`.
+
+    ```bash
+    az webapp config appsettings set -g MyResourceGroup -n MyUniqueApp --settings APPSETTING_DEFAULT_OS=bullseye
+    ```
+1. Deploy your application to the deployment slot using the tool of your choice (VS Code, Azure CLI, GitHub Actions, etc.)
+1. Confirm your application is functioning as expected in the deployment slot.
+1. [Swap your production and staging slots](deploy-staging-slots.md#swap-two-slots). This will apply the `APPSETTING_DEFAULT_OS=bullseye` app setting to production.
+1. Delete the deployment slot if you are no longer using it.
+
+##### Resources
+
+- [Debian Long Term Support schedule](https://wiki.debian.org/LTS)
+- [Debian 11 (Bullseye) Release Notes](https://www.debian.org/releases/bullseye/)
+- [Debain 9 (Stretch) Release Notes](https://www.debian.org/releases/stretch/)
+
 ### Limitations
 
 > [!NOTE]