Using the Sitecore bootloader to add Redis to an Sitecore 8.2 XP0 installation

The Sitecore bootloader is a nifty little-underdocumented thing that can be used to easily extend a Sitecore installation. When you'll install EXM using the web deploy packages, you'll notice that it has to add some connection strings to the ConnectionStrings.config, but you cannot modify that file without restarting the application. So I was wondering, how does that work.
It appears that the bootloader scans directories and can apply xdt transforms to all configs. Just by placing a file called ConnectionStrings.config.xdt on the Azure WebApp in the following folder: App_Data\Transforms\Redis\Xdts\App_Config, the bootloader will try to match the filename without xdt and run the transformation. So the path after Xdts should match the folder structure from your site root.
The Redis package does exactly the same: I've created a WebDeploy package containing this file, so we can deploy Redis to Sitecore without any modifications to the Sitecore installation beforehand.

The content of the xdt file:

<?xml version="1.0"?>
<connectionStrings xmlns:xdt="http://schemas.microsoft.com/XML-Document-Transform">
 <add name="redis.sessions" connectionString="Redis Connection String" xdt:Transform="Insert" />
</connectionStrings>

By adding a parameter to the web deploy package called 'Redis ConnectionString' we can now push the Redis connection string to the web deployment package.

{
  "name": "[concat(variables('singleWebAppNameTidy'), '/', 'MSDeploy')]",
  "type": "Microsoft.Web/sites/extensions",
  "location": "[parameters('location')]",
  "apiVersion": "[variables('webApiVersion')]",
  "properties": {
    "addOnPackages": [
      {
        "packageUri": "[parameters('redisMsDeployPackageUrl')]",
        "setParameters": {
          "Application Path": "[variables('singleWebAppNameTidy')]",
          "Redis Connection String": "[concat(reference(resourceId('Microsoft.Cache/Redis', 
                   variables('redisCacheNameTidy')), variables('redisApiVersion')).hostName, ':', reference(resourceId('Microsoft.Cache/Redis', 
                   variables('redisCacheNameTidy')), variables('redisApiVersion')).sslPort, ',password=', listKeys(resourceId('Microsoft.Cache/Redis', 
                   variables('redisCacheNameTidy')), variables('redisApiVersion')).primaryKey, ',ssl=True,abortConnect=False')]"
        }
      }
    ]
  }
}

During the first hit of the site, the bootloader will scan the App_Data\Transforms directory. The bootloader then runs an installer in a separated process on the Web App to apply the transformation.

Supporting code:
https://github.com/luuksommers/sitecore-xp0-redis

Happy caching!
Luuk