Quite often I find myself on edge.launchpad.net instead of the 'usual' launchpad. It looks exactly the same as traditional launchpad, so I wonder if there is any difference. This happens usually when I go to launchpad by clicking a link on a third party website. Somehow people prefer to link to the edge subdomain of launchpad, or at least I have such impression.
So what exactly is the edge.launchpad.net? And why some people prefer it than the usual launchpad.net?
Looking for information I was always redirected to https://help.launchpad.net/LaunchpadReleases and https://help.launchpad.net/BetaTesting , but I didn't find there anything about edge. I guess it may be something like a testing environment, if yes, than how does it differ from staging.launchpad.net and qastaging.launchpad.net?
There is absolutely no difference between edge.launchpad.net and launchpad.net. It used to be used for easy testing of new Launchpad code, but is now deprecated.
Back in the olden days (well about twelve months ago) then anyone could join a special group on Launchpad. If you were a member of this testing group then whenever you visited launchpad.net you were automatically redirected to edge.launchpad.net. Because of this automatic redirection, a lot of people forgot about it, and posted links to edge.launchpad.net all over the place. Although this wasn't harmful (anyone could go test on edge.launchpad.net) I can see people being confused by it.
For some reason they've let the domain hang around for a while, to be honest they've probably just forgotten about turning it off (well redirecting everyone back to launchpad.net).
Anyway, the point is that right now, you get exactly the same results whether you view edge or the main domain.
It was something like testing environment -- https://answers.launchpad.net/launchpad/+faq/75 and members of launchpad-beta-testers had this by default, but it's now deprecated -- http://blog.launchpad.net/general/edge-is-deprecated