Which user needs read access to serve web pages in ec2 instance?

Question

Which user needs read access to serve web pages in ec2 instance?

Context

I'm trying to make my website more secure by changing directory/file permissions.

I'm a bit new to this whole permission thing so for right now I've only changed the permissions on a single file, index.php, to 770 which used to be 777. I created a new user and group, both named "my_site". (I know 770 isn't the best, I'm just experimenting little by little to get a better understanding.)

I then changed the owner and group of index.php from "ec2-user" to "my_site".
Now the web page doesn't show up.

I tried added the users "ec2-user", "apache", and "root" to the group my_site.

There are no other users in the group ec2-user so my deduction is that it must've been some "other" user which was reading from index.php which is no longer possible due to having 770 as the permissions.

For the life of me, I can't find out who exactly is this "other" user so I can add them to the group.