Removing the connections as I mentioned in the last message solved the problem only temporarily (and to be honest I don’t know how).
When the issue resurfaced, I dug a little more and ended up on this thread: https://groups.google.com/forum/#!msg/ansible-project/8p3XWlo83ho/KlIqch_UxTEJ
To summarize, I had UserKnownHostsFile /dev/null, so ansible smellt an empty known_hosts file and run in a serial fashion to allow me to type “yes” atfer each host connection.
Setting ansible_host_key_checking=0 solved the issue for good for me.
That explains why David’s issue was solved upgrading: ansible 1.3.3 had support for hashed hosts that ansible 1.2.3 hadn’t.
I really hope the solution proposed in the other thread will be accepted: a warning about the cause of the serial behaviour would have been priceless.
Silvio