On March 31, 2017, support of CentOS 5 has ended.
And therefore, we cannot perform yum on CentOS 5 official images because yum repositories for CentOS 5 is deleted.
This image rewrites yum repository urls in /etc/yum.repos.d to vault.centos.org.
You can use this image as drop-in replacement of official centos:5 (centos:5.11).