The hostname format used by fig creates names that are not strictly valid.

Current pseudo-code:

name = '_'.join([project, container, instance_num])

This generates names like cluster_hadoop_1. Underscores are not valid (though in practice most components are tolerant of this).

Valid names should match [a-zA-Z0-9\-]+.

I came across this error when trying to test out some hadoop/hdfs containers and hadoop bailed with an exception saying that hdfs://flume_hadoop_1/ was not valid URI (even though it was in /etc/hosts and ping flume_hadoop_1 worked just fine).

See: http://en.wikipedia.org/wiki/Hostname#Restrictions_on_valid_host_names

Changing this to dashes is easy, but it would break existing configurations that depend on hard coded container names.