Alien alias
This module allows you to create customizable URL aliases that redirect to external or internal locations. These aliases can be redefined over time and are processed early in the Drupal boot process for efficiency. Optionally, it can track requests to these aliases and set query parameters.
This module provides a means of creating a URL alias in a Drupal site that points to an external location (although it could be internal). It allows the alias to be redefined which means it can be set to point to a different location at some time, either temporarily or permanently.
The check for, and redirection of, an AlienAlias is performed early in the boot-up sequence of Drupal by default, which means it has minimal impact on resource usage - compared to having to fully boot-up Drupal before being able to redirect. (This is optional on a per-alias basis, or globally.)
Optionally, the module will keep stats on the Alien Alias requests, and a query parameter can be defined to indicate, for example, the source of the request.
How it works
Each AlienAlias is an entity so any number of them can be added.
When a request comes in, and before the site fully boots-up, the path is checked to see if it's an alien alias (only a single DB check is required). If it is, the user is immediately redirected. If not, normal site boot-up continues.
Every AlienAlias has a Drupal 8 router entry which means Fast404 will not claim the URL does not exist.