The Codebase Is in Git

The version control system (VCS) is the heart of the process. At the most basic level, a VCS allows developers to keep track of all the changes made to a set of files and enables them to roll back to specific points in time in case something screws up. In some systems, like Subversion, the code is checked out and then checked back in from a central repository. If there is a conflict between two developers’ files (for example, both of them edited the same line of code), then the two version must be merged. This can be a painful process.

In contrast, distributed version control systems (DVCS), like Git, are the heart of most new development processes. Rather than having a central, master copy that makes it difficult and expensive to merge a lot of contributions from developers, a DVCS makes it simple (well, simpler!) to have multiple people all working on the same codebase simultaneously in different branches, and these branches can be easily merged in a master branch.

While there are many different work styles, such as Git flow, the basic DVCS process is:

• There is an agreed-upon master repository, which is often on a public service like GitHub or BitBucket, or an internal server like GitLab or Mercurial.
• Each developer clones the master repository to his or her local machine.
• The developer creates a new branch, usually for a specific feature.
• The developer makes commits against the local copy.
• Once the feature is done, he or she merges the branch back into the master branch and pushes the change back to the master.
• Other developers pull from the master branch and merge their branch.
• The merged copy preserves the full version history of all the distributed copies.

In addition to these coordination functions, most version control systems also offer a feature called a hook. A hook is a process that fires once a specific event, like a commit, happens to the repository. Hooks can be defined in the repo itself, but also in the hosting service. For example, GitHub lets you define “service” hooks that are called whenever a specific event occurs. These hooks are the tie-in to the continuous integration (CI server).