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 into 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 copy of the repository.
- 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).
Here are the key version control systems:
- Git. "Git is a free and open source distributed version control system designed to handle everything from small to very large projects with speed and efficiency."
- Mercurial. "Mercurial is a free, distributed source control management tool. It efficiently handles projects of any size and offers an easy and intuitive interface."
Hosting services provide a central point where you can manage and store all your code repositories. In addition to raw code storage, they usually offer features like issue tracking, collaborator management, and other process-oriented services.
The following table lists hosting services managed by a 3rd party. The pricing model is typically based on a block of repositories for a monthly fee.
- GitHub. One of the largest and most successful Git hosting services.
- BitBucket. Atlassian's Git hosting solution.
- GitLab.com. A hosting service based on the popular open source project GitLab HQ.
- Gitorious. Similar to GitLab, a hosted version of an open source tool that you can install and maintain yourself.
- Beanstalk. Beanstalk hosts Git and SVN repositories. It also provides webhooks and many built-in integrations for continuous deployment and automation.
These are services that you can install and manage in your own environment:
- GitLab. "Project management and code hosting application."
- Gitosis. "software for hosting Git repositories"
- Gitorious. The self-hosted version of gitorious.org. (It's a Rails app.)
- Kallithea. Source code management system for Git and Mercurial.
- Stash. On-premises source code management for Git by Atlassian.