If the region parameter is not specified when invoking spark-ec2 (spark-ec2.py behind the scenes) it defaults to us-east-1. When the cluster doesn't belong to that region, after showing the "Searching for existing cluster Spark..." message, it causes an "ERROR: Could not find any existing cluster" exception because it doesn't find you cluster in the default region.
As it doesn't tell you anything about the region, It can be a small headache for new users.
In http://stackoverflow.com/questions/21171576/why-does-spark-ec2-fail-with-error-could-not-find-any-existing-cluster, Dmitriy Selivanov explains it.
I propose that:
1. Either we make the search message a little bit more informative with something like "Searching for existing cluster Spark in region " + opts.region.
2. Or we remove the us-east-1 as default and make the --region parameter mandatory.