You are browsing a read-only backup copy of Wikitech. The live site can be found at wikitech.wikimedia.org
On Labs you have projects; projects can be used to spawn virtual machines (VMs), which are called instances. You can have as many as you want, up to the limit. You set up a web server on the instance.
For the instance to actually be accessible over the public Web, you need to set up a Web proxy; this is where you get your subdomain such as something.wmflabs.org.
If you're just setting up basic MediaWiki, you don't need to bother with MediaWiki-Vagrant.
You could just do it on Tool Labs, where all the sysadmin work is done for you, but it's harder to do things on Tool Labs where it is assumed you have full access to the server. MediaWiki is much easier to set up with full access to the server, making Tool Labs less than ideal.
Python Flask applications work quite well on Tool Labs.
Example: https://tools.wmflabs.org/mediaplaycounts/api/1 << Flask app running on Tool Labs
In this case, you set up Kubernetes and it runs the application. Kubernetes is a mysterious and magical thing.
It would be NICE if you could just set up MediaWiki with Kubernetes. Bawolff may have tried and may have found a security vulnerability.
In an ideal world you don't set up a whole labs instance except as a last resort.