How to handle a server outage if I have two sites

[Ehren]

I operate a web application.  It consists of two sites, www.mysite.com and app.mysite.com.  As you might imagine, www is used for marketing purposes, and it's our main organic search entry point. The app.mysite.com domain is where our application portal is for customers, and it is also where our login and registration pages are located.

Currently, www.mysite.com is experiencing a catastrophic outage and is returning 504 errors, but app.mysite.com is on a totally separate system with a lot redundancy, and is doing just fine.

If we get traffic from referrals or search, we want that traffic to be able to login and register, so we've replaced the 504 error with a 302 redirect to app.mysite.com until the situation is resolved.  This provides the best possible experience for users (nothing's worse than a 504).  How will this affect SEO?  Is there something other than a 302 that I should be doing with the broken www.mysite.com domain?

[icecarats]

Depending on the longevity of the outage, I would say no, that you're using 302 appropriately. In fact I'm trying to think what else you could do that's better, and really can't come up with much (url rewrite so the end user isn't confused by app.mysite.com versus www? and that's reaching). If the outage is short term (e.g. less then 24-48 hours) I really can't think of a better solution than 302. Google dislikes it when you flip 301s off and on at the drop of a hat obviously.

[loopyal]

I would also use a 302.

As long as it doesn't last too long, you should be OK.

If you think it may last longer, you could change your DNS to point to the other location, but you should drop your TTL on DNS so it is a fast changeover to move it back.

This kind of thing is best set up and tested when there are no problems, on another domain, and then test it for real sometime when you have worked out exactly what to do.