Observations and insights from the Security PS Team.

ASP.NET Core and Docker Update: Docker Compose!

Previously in ASP.NET Core, PostgreSQL, Docker, and Continuous Integration with Jenkins, I wrote about my experience getting started with ASP.NET Core and Docker. In that post, I was running a script to stop and remove my previous containers each time I deployed, and I had separate scripts to build and run each Docker container. In a recent conference video, a speaker referenced Docker Compose, and I'm so glad he did. It simplifies my set up greatly! This post describes the changes I made to my project to use Docker Compose.

I reused all my previous DockerFiles and I needed to reference them in a docker-compose.yml file in the root of my project. Here's that file:

After trying to run this (which I will get to later), I discovered that there were some differences in how linking two containers works. Instead of automatically providing environment variables that reference the linked containers, it sets up hostnames that match the services above. So, I needed to make a few changes to my configuration files. First, I updated my appsettings.json file to change the host referenced by the ConnectionString.

In the haproxy.cfg configuration file, I referenced the web1 and web2 hosts. I also learned how to correctly configured the proxy to set a cookie and direct users to the same Kestrel instance each time.

With those changes, I was ready to build and run all the containers.

Since I'm deploying a new instance of the database server and an empty database, I also need to run my Entity Framework Migrations. So the next step is to run "docker-compose exec -d web1 dotnet ef database update".

Finally, when I need to stop and remove the containers to make way for a newer build, Docker Compose takes care of that as well.

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