If you search online for using SSH keys with Docker, to access private Github repositories, you will get a lot of search results, but the solutions you’ll find are almost all out of date, insecure, or fragmentary (i.e. they provide a small snippet of information but not a complete solution). Given how popular both Docker and Github are, I found this quite surprising. We recently had to set up Docker with a Rails application that fetches gems from private repositories. We’re also using Docker Compose, which added to the challenge. This comment on the Docker project, which is from February 2021, unfortunately is still accurate:

There are several questions and answers out there about how to pull from a private repository (using the hosts ssh key & config). A lot of them are not working, not secure or unanswered

After several hours of research and testing, we have a good solution to share. But first let’s take a look at the different approaches to consider.

Recently I worked on a client project that required me to implement good code conventions across the project. One of the tasks besides implementing the Rubocop standard cops was to write a custom cop for two different Datetime methods, so in this article I will explain how I created a custom Rubocop cop that solved that problem.