I'm publishing as I go on LeanPub; I've written a little about the process so far on Server Check.in[1]. I'll probably work on getting the book on Amazon/Kindle before it's in its '1.0' state, but LeanPub will always have the latest version of the book (including after the '1.0' release).

[1] https://servercheck.in/blog/self-publishing-my-first-technic...