Re:Amazon EC2 currently down. Affecting Heroku, Reddit, Others
by ConstantineXVI on Monday October 22, 2012 @02:33PM
(#4684635)
Note that the region-1[a b c d & such] designations are randomized per account; my us-east-1d won't (necessarily) be the same as yours or anyone else's.
Also, the availability zones are disparate in terms of what they can support. A great number of my instances are in 1d because of unavailability in others.