At any rate, our AWS hosts are mostly Centos 6.3, which come with the baseline Python 2.6.6
Attempting to use locust.io on these hosts with the system Python 2.6 quickly brought about:
"gc refcount related crash when loading web UI under Python 2.6.6"
Thankfully, getting Python 2.7.3 running as an altinstall was pretty simple and fixed this issue - here's the steps it took (you may also need other Developer related packages...):
yum install readline-devel
yum install libevent
yum install libevent-devel
yum install zlib-devel
yum install bzip2-devel
yum install openssl-devel
yum install ncurses-devel
tar xf Python-2.7.3.tar.bz2
pip-2.7 install -U locustio
Voila, no more gc crash when launching locust!