Separating dependencies

In the last chapter I Dockerized the legacy NerdDinner app and got it running, but without a database. The original application expected to use SQL Server LocalDB on the same host where the app is running. LocalDB is an MSI-based installation, and I can add it to the Docker image by downloading the MSI and installing it with RUN commands in the Dockerfile. But this means that when I start a container from the image, it has two functions: hosting a web application and running a database.

Instead I'm going to package the database in a new Docker image, run it in a separate container and use Docker's network layer to access the database container from the website container. SQL Server is a licensed product, but the free variant is SQL Server Express, which is available from Microsoft as an image on Docker Hub and comes with a production license. I can use this as the base for my image, building on it to prepare a preconfigured database instance, with the schema deployed and ready to connect to the web application.