Today, we are going to list the 12 factors recommended for better web application development. You can see these 12 factors as a checklist to de & deploy your app easily and shortly.

12 factors

What is it ?

According to wikipedia, The Twelve-Factor App methodology is a methodology for building software-as-a-service applications. These best practices are designed to enable applications to be built with portability and resilience.

Why

The main goal is to remove MANY problems when deploying your apps.

The 12 :

• Only one codebase for your app This codebase can be used for many deployments, using configuration files out of the codebase (or env variables)
• All dependencies are declared No implicit reliance on system tools or libraries. For NodeJS, this implies to always commit your package-lock.json file.
• Configuration that varies between deployments should be stored in the environment If you realise that two of your codebase instances differs, it has to go in the env
• Backing services (and external API for instance, or a DB) are treated as attached resources You should be able to plug / unplug simply modifying the environment during the execution.
• Build, release, run : nothing more, nothing less
• Applications are stateless processes So persisting data are stored on a backing service, never in Sessions or server-RAM related storage. Main goal is to deploy mulitple instances of your application (when your load ramps up) using auto-scaling and so on… a user loged with session var to a specifi server would be discotnected if the load balancer sends its following request to another server replica (because sesssion vars stay inside the server)
• services are available on specified ports Note: Using docker eases a lot this requireements
• Concurrency => scale individual processes Scaling with more machines is infinite, while getting more RAM on one machine is limitied.
• Fast startup and shutdown Fast autoscaling
• Dev/Prod parity All environments are as similar as possible, so that there are no suprises with specific conf / missing package
• Applications produce logs as event streams and leave the execution environment to aggregate. => use the defualt stdout for logs. The app mustn’t care about the log service which will handle it.
• Any admin tasks should be kept in the codebase This way, there are no surprises. the Codebase is enough to manage everything.

Reference

Wiki summary
Official 12-factor-app website
App Checklist from Michael Bitard