Jaggies Weekly

Keep your configs for each environment

The app's configuration is everything that may vary between environments. This includes:

• System resources like databases, Memcached, and backing services;
• Credentials for external services such as Amazon S3 or Twitter;
• Environment-specific values such as the hostname.

The Twelve-Factor methodology strongly advocates for separating configuration from the code. This is primarily because configuration values may differ between environments while the code remains constant. A useful way to determine if configurations are properly extracted from the code is by considering the scenario of making the codebase open source. If the credentials need to be managed, the configurations might be compromised.

Another approach involves using configuration files not included in the version control system, such as config/database.yml in Rails. While this is a significant improvement, it is not recommended because there's a risk of accidentally pushing these files. Additionally, configuration files often scatter across different locations, making maintenance challenging. Moreover, these config files tend to be specific to a particular language or framework.

Another practice to avoid is grouping configurations into environment-specific sets. Apps tend to categorize configurations into named groups for different environments. However, this method doesn't scale well. As the project expands, developers might introduce their own custom environments, leading to an explosion of configurations that complicate deployment management.

The Twelve-Factor methodology suggests storing configurations in environment variables. Environment variables are easy to modify between deployments without requiring changes to the code. They compel setting up independent configurations for each deployment environment, minimizing the chance of accidental check in the codebase repository. They don't aggregate into 'environments' groups, they are language- and OS-agnostic standards and provide a scalable model as the app naturally expands to more deployments.

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!