Shorts

Firstly, make sure you have ssh access to the server (dev, test and/or prod). Your ssh command looks something like this: ssh user@your-website.com or ssh user@100.230.222.122. Drush alias works by using this username and domain/ip address combination to login to the server and execute the command and then return back to your command line. In your project root, create a drush folder and inside it, create a sites folder. Now you put your site alias config in that folder.

There is a tool called siege which you can install quite easily.

sudo apt install siege -y # debian based systems
sudo pacman -S siege # arch based systems
sudo dnf install siege -y # redhat based systems

Once you have installed siege, the following commands can be used to load test:

Shutdown functions are functions that are executed after the current scope has been "shutdown". Say, you want to run a function after another function has completed execution, then this is the way to go. It is also a way to make PHP web requests somewhat asynchronous. In a Drupal context, say you are sending a request, that triggers a function. But you do not want to wait for the response or you want the function to start executing after the request has returned a response.