Bootstrapping ProcessWire: What's the difference of including index.php versus multi-instancing?

[salmiak]

What are the differences between using the including and bootstrapping and multi-instance approach for using ProcessWire in an external script?

Obviously multi-instance would let you use more than one installation and in my environment multi-instance seems to perform (much) better under load.
Why would I choose one over the other?

[kongondo]

2 hours ago, salmiak said:

What are the differences between using the including and bootstrapping and multi-instance approach for using ProcessWire in an external script?

Let's say you have Site A, Site B and Site C. Site A and Site B are ProcessWire sites whereas Site C runs on something else (Laravel, WP, some PHP forum, etc).

You can use bootstrapping/include to access Site A whilst in Site A when in a CLI environment. You can also use bootstrapping to access Site A inside Site C.

To access Site B inside Site A or vice versa, you use multi-instance approach. i.e. one ProcessWire inside another ProcessWire instance (site).