I'll be talking about 12-Factor App Manifesto that has been published by Heroku. This isn't about directly PHP but my purpose is showing a culture and acting by developing application smoothly.
I'm going to mention experience that we had in my current company how we struggle to obey these principles.
Software development is divided by 2 parts such as development and operation. These 2 parts gather their knowledge and they try to create a modern applications. In this case, there are 12 principles to create an application/service to get rid of problems, issues. We will get monitoring, deploying, testing, building, releasing, scaling and so on. 12-Factor app manifesto really eases to developing services/applications during whole process.