If you have to take down your website for any reason, such as to do backend maintenance that requires a site be taken offline or if you are re-doing an entire site after it has been hacked, it is important to use a 503 server status code for SEO reasons.

Using a 503 server status code tells Googlebot and other search crawlers that yes, the site is still here, we are just temporarily down for maintenance related issues and will be back online soon.  Done correctly, you can even specify when the maintenance or downtime is scheduled to be over, so that crawlers can return at this time.

If you do not use a server status code and start delivering 404s to Googlebot, especially if the downtime extends longer than a couple of hours, Googlebot could handle those 404s as meaning the site has been removed, which will have a serious impact on rankings even when the site comes back online again.

The question was raised in today’s webmaster hangout where someone had their site hacked and were forced to take it offline for 24 hours while they fixed it.  And since they were serving 404 errors, this resulted in major ranking issues that have still not resolved themselves.

If you recognize that this is happening and you have the ability to do this, I’d strongly recommend using a 503 result code for all requests that come in from search engines and from users.

With a 503 we know that this is a temporary situation and you’re working on resolving this as quickly as possible and Google will say fine, we’ll just come back and look at it again in a couple of days.  Whereas if you take the server down completely and serve 404s for example, then Googlebot will come and say “whoa, looks like this website doesn’t exist anymore, these pages don’t exist anymore, I’ll drop them from my index.”

So if there is a way that you can serve a 503 when your site is hacked or are taking it down for maintenance, that’s really the best thing to for that.  That way you shouldn’t really have any impact with regards to your rankings or your indexing.

If course, if you leave the 503 for a longer period of time, if you take your website offline for a couple of weeks, then we’ll assume this is a permanent state and not just something temporary that we can look over.

Bottom line, if you want to protect as many of your rankings and indexed pages as possible, serve Googlebot a 503 server status code, but only use it for a reasonable period of time.