One codebase tracked in revision control, many deploys

A codebase refers to the main code definition that serves as shared code among developers for ongoing feature development. Typically, a codebase is stored in a code repository managed by a version control system like Git, Mercurial, or Subversion.

The codebase is a single repository or any set of repositories that share a root commit.

There exists a one-to-one correlation between the codebase and the app:

• If there are multiple codebases, it does not qualify as a single codebase but rather constitutes a distributed system. Each component in a distributed system is considered an app, and each can individually adhere to the Twelve-Factor principles.
• Having multiple apps sharing the same codebase violates the Twelve-Factor approach. The recommended solution is to modularize shared code into libraries that can be included through the dependency manager.

Per app, there exists only one codebase, but numerous deployments of the app can exist. A deployment refers to a running instance of the app, which commonly includes instances in production, staging, testing, and an additional local instance for each developer.

While the codebase remains consistent across all these environments, there might be different active versions in each environment due to ongoing feature development during the development cycle.

This Twelve-Factor App post series is a means for me to consolidate the knowledge I've gained while studying these rules. Please feel free to visit the site for more detailed explanations. That's all folks!