If you go far enough back in time (this dates back to at least 2011), it's arguing against things like:

For port binding, for example, it used to be that you'd deploy your app to the web application container, rather than bundling them together. e.g., deploying your WAR file to Tomcat, rather than building a self-executing JAR which included Tomcat. The wording is a bit odd, but I think they were trying to make the point very generic, and not specifically about the Enterprise Java world.

For the backing resources, it's a combination of point 3, config often living inside the codebase, applications just shelling out to /usr/sbin/sendmail or what have you, and applications living on the same host as the DB, such that bringing up a new application necessarily required bringing up a new DB as well. Which also made it hard it to scale horizontally.

The whole "12 Factor" thing was partly because Heroku had specific solutions for all of these, so going down this road made it much easier to then sell Heroku, and partly because they really were frustrating. I'd say that the port binding one is more targeted at, say, WebSphere, and all that came along with it, such as sharing a single heap across multiple apps, needing to talk to the WebSphere admins to change configuration, needing to use a "lite" version of WebSphere to test locally, if that was even possible, and so on.

They sound super-obvious these days, but at the time, for a lot of us, they were really nice to see.

I think backing services as attached resources was opposed to the practice of having your DB, and cache, and whatnot managed and maintained by a completely separate team and not really treated as part of the application. Even the schema changes.

The port binding was really a response to tomcat or modphp being modules in the webserver, as opposed to hosting their own web service internally. This was before nginx took off, and proxying to internal application ports was common.

edit:

I was wrong about the backing services, it seems it is really about treating them as configurations and being able to swap them out without making code changes.

https://12factor.net/backing-services

> Why is that interesting and not trite?

The same reason many older films seem cliche - because they were the first to do it, and it's accepted standard now. Heroku very much shaped how we think of "cloud applications", autoscaling, and containerization.

Doctors didn't wash their hands between inspecting corpses and doing surgery.

Drivers protested against seat belts that would save their own lives.

Times change and hindsight is 20/20. Let's just say 10 years ago I worked at a company that broke all 12 factors.

In older architectures you would expose services as libraries and everything ran in one UBER process… eg JBoss and ASP.. it also covered off on web server processing like cold fusion and php.

I think you gotta look back to how web servers worked before containers.