I made a list of all domains that resources on my site may use.
How do I add the link-tags for dns-prefetch for best practice?
1) Can I simplify life and output them all on every page? How painful is it to prefetch domains that may not be needed on the user's visit (e.g. a youtube player on some sub page). My thought is that dns resolving is cached in the browser for ~90(?) minutes...
2) Should I prefetch only domains that are referenced in the html directly, or also those that are needed after an action like click on a play button (e.g.) googlevideo.com for when a youtube player is started).
3) How to handle CDN subdomains like s.ytimg.com? I guess it's not enough to prefetch ytimg.com (if not even useless when this domain is never used alone)? All hope is lost for unguessable subdomains like a1339.phobos.apple.com I guess.