service apache2 reload
Service vs Systemctl
You may have noticed that some tutorials suggest reloading apache2 (and other services) using a program called "systemctl" (rather than "service").
Basically "service" is a program that's used for bac commands like: start, stop reload. But "systemctl" is a newer program that offers more functionality. "Service" has not been deprecated, you can continue using it.
Frankly, I find "systemctl" to be a clumsy, ugly name, so I prefer to use "service" whenever possible.
Restart vs Reload
The "restart" commands stop the apache2 and then starts it up again--there will be some downtime for a couple of minutes.
The "reload" commands keeps the server running while reloading configuration files.