Disabling e-tags
E tags were created to define a consistent way of letting the user know when files had been updated on a server. What this basically means is each file such as an image, CSS or javascript file is given a number called it's e-tag. The browser receives the number and stores it against the file that was downloaded. If the user decides to view the page again, the file's e-tag on the server is checked against the e tag that is stored in the browser. If they are different, a new version of the file is downloaded. If they are the same it means the file on the server is the same and there is no need to try to download a newer version.
Sounds like a great idea except for one nasty problem. The e-tag is worked out based on a number of factors including the id of the server it is on. If you are running multiple servers for load balancing purposes, what will happen is each file on each server will have a different e-tag. Therefore the user will download files again if they happened to be requested from a different server than the previous request.
Therefore we should not use e-tags and disable them in our htaccess file. This is how you do it:
### turn off etags ###
Header unset ETag
FileETag None
