Apache is mentioned there because some general sections are included in that page. For example the section to manage the services is the same in all our apps and it's only an example.
Regarding the Varnish configuration, we use the same section in all our apps with Varnish but we divide the information between Apache and NGINX. I'm going to notify our Documentation team to improve the user experience when using our doc pages though.
If Varnish is disabled, you can enable it by following this information
I hope this helps