The problem is, that haproxy does a healthcheck that expects a 200 OK response. EC2-API however returns 400, if not authenticated. I submitted a fix upstream.
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory, and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.
https://access.redhat.com/errata/RHEA-2017:3462