After installing EPEL repository and enabling EPEL, I tried the following:
# yum install docker-io || yum --enablerepo=epel install docker-io
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
* base: mirrors.btte.net
* epel: mirrors.yun-idc.com
* extras: mirrors.btte.net
* updates: mirrors.btte.net
No package docker-io available.
Error: Nothing to do
In CentOS 7, how can I install docker?
As described here, docker is inside the CentOS-Extras repository of CentOS 7 and can be installed without the need for enabling EPEL.
Please note: As of CentOS 7, the correct name of the package should be simply docker, while in the EPEL repository for CentOS 6, it is yet called docker-io.) I guess that's the problem why it fails for you. Hope this helps!
Some additional comments (thanks to @Martin Preusse for the hints):
The packages in the extras repository are a little bit outdated right now. Available version is 0.11.1, while the current stable version of docker is 1.2.0.
While docker was available in the EPEL repository for CentOS 6 as docker-io (because docker is conflicting with the package name of a system tray dock), it is not available in the beta EPEL repository for CentOS 7. And even worse: The version in the EPEL for CentOS 6 is 1.1.2 and much newer than the current version in the official extras repository of CentOS 7.