Usually when I perform maintenance that requires briefly taking my site down, I put up a 503 page using something similar to How can I make Nginx return HTTP 503 when my proxied app server is down?.
However, I'm about to upgrade my Digital Ocean droplet to a larger size, so the 503 error won't get sent. One way I could achieve this is to put my 503 error page on a separate droplet and redirect my DNS to this other IP address while I upgrade the droplet. However, I'm afraid this might raise flags with Google if they crawl my site then.
How should I go about notifying users and bots that I'm performing maintenance when I have to take down my entire server?