The FROM statement declares that we want to lay some instructions on top of the microsoft/mssql-server-windows image. The beauty of this approach is that when I pull down a new version of the microsoft/mssql-server-windows image, my image will be updated too. The microsoft/mssql-server-windows Dockerfile does the same thing with the microsoft/windowsservercore image.
The rest of the Dockerfile sets some meta data, downloads the installer and adds the Advanced Analytics feature.
SSIS, SSAS, SSRS or any other SQL Server feature could be added to a containerised SQL Server deployment in the same way.
With this approach, you do run the risk that upstream changes will break your image, but for something like this, it’s a very useful approach.