Although simple, this is a very powerful and core concept in developing SaaS. Before I jump right in, I wanted to define what a codebase is.
A Codebase is a collection of source code that is used to build a software system, app, or component. (1)
12-Factor further adds:
A codebase is any single repo, or any set of repos who share a root commit. (2)
I was working on an IBM ECommerce Website in 2013 that violated this rule early in the development cycle. The business requested a second version of their Ecommerce site for a recent business partnership. A quick decision was made to create a second branch in the same codebase rather than to fork it. This made the stand-up of the second website easy. It allowed the business logic and deployment to remain the same, but the UI could be maintained independently. Our engineers would develop business logic on the main branch, while our web designers split their work between the new branch and main.
As new business logic was being added to the original website, all the changes were expected to be ported to the new site. Our engineering team was in charge of merging down changes from the main codebase to the second branch. The UI team, although not intentionally, would often modify business logic in the second branch. This lead to merge conflicts and several meetings about what sections of code should be maintained by which teams.
By violating ‘A codebase is… a set of repos (that) share a root commit’, we had caused a maintenance nightmare. Branching created a second codebase, violating this rule and requiring us to constantly curate the competing commits between the two branches.
If we had shared a codebase, feature parity would have been infinitely easier. With two ‘root’ commits in the mix, we suddenly had many more decisions to make.
Which version of a conflicting change should win?
Who determines which changes should win?
Should we have both changes exist independently of one another?
It was a lot of rework that could have been avoided by maintaining one ‘root’ commit.
One thing I didn’t touch on as much as I wish I had is how deploys relate to codebase. I have a feeling this will come up again in an upcoming article on config, so stay tuned!