Code base

The first factor is related to the source code, where it is kept, and how it should be kept. Every change in the code must be saved and tracked into the source code repository. Nowadays, there are plenty of choices: GitLab, GitHub, Bitbucket, Stash, and the old SVN (it's a revolution, so switch to Git). All of the code, including infrastructure as code, should be versioned, and each version potentially corresponds to a deployment in some environment.

Long story short, have a source code repository, and it is better to have an open source and widely adopted solution.