Recently I built docker images for omnibus builds. Omnibus packages must be built on the target distro so I needed images for centos, debian and ubuntu. Usually I build such docker images on my laptop which is running Ubuntu; I try to make the builds as repeatable as possible using the excellent packer tool and when I publish images I build them again (using a build server) on cloud instances. In this case, I was using GCE CentOS 7 instance to perform the build and I was surprised when a build that was smooth on my laptop failed miserably. The build was for Ubuntu precise and the build step that failed was the the creation of the omnibus user. This was really weird since creating a user is a trivial task that was unexpected to fail.
