Description of problem: In an all-in-one environment I cannot use the resize with default install. allow_resize_to_same_host should be set to true. 2013-05-26 12:31:53.952 WARNING nova.scheduler.manager [req-88530a67-12ff-46b0-822d-0e62b7e37b01 eb830d8d6df048ef8368287a74802710 0b4f2254484840d8b38285f27cbb3440] Failed to schedule_prep_resize: No valid host was found. I do not see why the allow_resize_to_same_host would be problematic in multinode environment.
I think the idea behind this is that default values are supposed to make for a sane "vanilla" real world deployment, and I guess that this would mean a multi node set-up (having in mind that single node set-ups are considered purely proof-of-concept). From that point of view - I am reluctant to change this value in nova, but I encourage the reporter to report it against packstack for --allinone setups.
Addind to my comment #3 above - the reason this is a sane default for a multi-node setup is becuase it is a more common use-case to allow the scheduler to pick the host we will migrate/resize onto.