Magento – Magento 2 external library folder

Depending on the library, you may be able to use the very handy PSR-0-Autoloader Hackathon module.

https://github.com/magento-hackathon/Magento-PSR-0-Autoloader

The installation is pretty straightforward and there is a simple directive you will add to local.xml to get it working for your library.

There's zero reason to complicate something simple, unless you want to use composer's features at the cost of overhead of using coding for it. My library isn't even on composer and I don't want to leap through hoops to just include the library so this is simple and 2 steps, using library foo as an example.

1) put the library folder in lib/internal/ making it lib/internal/foo

2) in a module you have, put this in registration.php

require_once(BP.'/lib/internal/foo/include.php');

That's it, it works and won't mess up setup:di:compile. You can now use that library in your module. Obviously include.php has to exist and be the file that will load all your libraries code, some it might be index.php, or autoload.php