Merge pull request #268 from microsoft/psl-acr-migration-doc

docs: Comprehensive guide for migrating an Azure Web App Service

Author: Roopan-Microsoft

docs/container_registry_migration.md

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+# Guide: Migrating Azure Web App Service to a New Container Registry
+
+## Overview
+
+### Current Problem:
+- The **Document Generator Container Image** is being published in the **External ACR** (Azure Container Registry).
+
+### Goal:
+- The goal is to **migrate container images** from various applications to a common **CSA CTO Production Azure Container Registry**, ensuring all the different images are consolidated in one centralized location.
+
+---
+
+## Step-by-Step Guide: Migrating Azure Web App Service to a New Container Registry
+
+This guide will help you seamlessly switch the container registry for your **Azure Web App Service** from Azure Container Registry (ACR) to the new registry **`byocgacontainerreg`**.
+
+Follow the steps below to ensure a smooth migration.
+
+### Prerequisites:
+Before you begin, ensure you have the following:
+- Access to the **Azure Portal**.
+- The **container image** in the new registry is ready and accessible.
+
+---
+
+### Step 1: Obtain Details for the New Registry
+
+Before you begin, ensure you have the following information:
+- **Registry URL**: The URL of the new registry (`https://byocgacontainerreg.azurecr.io`).
+- **Image Name and Tag**: The full name and tag of the image you want to use:
+  - **Web App Image**: `webapp:latest`
+---
+
+### Step 2: Update Azure Web App Service Configuration Using Azure Portal
+
+1. **Log in to Azure Portal**:
+   - Open [Azure Portal](https://portal.azure.com/).
+
+2. **Locate Your Resource Group and Web App Service**:
+   - Navigate to resource group which you have created for Document Generator.
+   - Navigate to **Web App Service**: From the list of resources, find and select **App Service**
+
+3. **Go to the Deployment Center**:
+   - In the left-hand menu, click on **Deployment**.
+
+  ![Resource Menu](images/resource_menu.png)
+
+
+4. **Update Image Source**:
+   - Change the **Registry Source** to **Private**.
+   - Set the **Server URL** to the new container registry (`https://byocgacontainerreg.azurecr.io`), as shown in the screenshot below.
+   - Set the **Full Image name** to the relevant image name and tag:
+     - For Web App: `webapp:latest`
+
+   ![Deployment Center](images/deployment_center.png)
+
+5. **Save Changes**:
+   - Click **Save** to save the configuration.
+
+---
+
+### Step 3: Restart the Web App Service
+
+After updating the configuration, restart your **Web App Service** to apply the changes:
+
+1. In the **Web App Service overview page**, click on **Restart**.
+2. Confirm the restart operation.
+
+---
+
+### Step 8: Validate the Deployment
+
+1. **Access Your Web App**:
+   - Open the **Web App URL** in a browser to ensure it’s running correctly.
+---
+
+By following these steps, your **Azure Web App Service** will now use the new container from the **Document Generator registry**.
+
+For further assistance, feel free to reach out to your support team or log an issue on GitHub.
+
+---