Beyond the Twelve-Factor App

Chapter 1. One Codebase, One Application

The first of the original factors, codebase, originally stated: “One codebase tracked in revision control, many deploys.”

When managing myriad aspects of a development team, the organization of code, artifacts, and other apparent minutia is often considered a minor detail or outright neglected. However, proper application of discipline and organization can mean the difference between a one-month production lead time and a one-day lead time.

Cloud-native applications must always consist of a single codebase that is tracked in a version control system. A codebase is a source code repository or a set of repositories that share a common root.

The single codebase for an application is used to produce any number of immutable releases¹ that are destined for different environments. Following this particular discipline forces teams to analyze the seams of their application and potentially identify monoliths that should be split off into microservices.² If you have multiple codebases, then you have a system that needs to be decomposed, not a single application.

The simplest example of violating this guideline is where your application is actually made of up a dozen or more source code repositories. This makes it nearly impossible to automate the build and deploy phases of your application’s life cycle.

Another way this rule is often broken is when there is a main application and a tightly coupled worker (or an en-queuer and de-queuer, etc.) that ...