Lets assume I have a tumblr account:


Tumblr allows it so that it can point to www.sheehan.com if I enter an A-Record.

How does Tumblr scale this to millions of users? How is it possible to assign a single A-Record to multiple subdomains?

1 Answer 1


basically there is an apache/whatever header directive that redirects it to your site. It will be a very small amount of data ( check out 301/ moved permanently headers for more ).

For scaling it to millions, this kind of data ( username (key) -> custom domain(value) ) you could store the data for all the users in a memory mapped hash and then put a squid ( or similar ) proxy to cache.

  • I think it's actually key=domain, value=user -- seems like a lot more effective to me.
    – user1686
    Nov 23, 2010 at 15:21
  • from username i mean "sheehan.tumblr.com" and by domain i mean "sheehan.com" Nov 23, 2010 at 16:28

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