CentOS7 に Dockerをインストールする手順です
これだけ。

# yum update
# yum install docker-io

# docker -v
Docker version 1.3.2, build 39fa2fa/1.3.2

超簡単です。

Remote APIも有効にしておきます

# vi /etc/sysconfig/docker

    # Modify these options if you want to change the way the docker daemon runs
    OPTIONS=--selinux-enabled -H tcp://0.0.0.0:4243 -H fd://

    # Location used for temporary files, such as those created by
    # docker load and build operations. Default is /var/lib/docker/tmp
    # Can be overriden by setting the following environment variable.
    # DOCKER_TMPDIR=/var/tmp


起動します。
ついでにRemoteAPI経由での接続も確認。

# systemctl start docker
# docker version
     Client version: 1.3.2
     Client API version: 1.15
     Go version (client): go1.3.3
     Git commit (client): 39fa2fa/1.3.2
     OS/Arch (client): linux/amd64
     Server version: 1.3.2
     Server API version: 1.15
     Go version (server): go1.3.3
     Git commit (server): 39fa2fa/1.3.2

# docker -H tcp://localhost:4243 version
     Client version: 1.3.2
     Client API version: 1.15
     Go version (client): go1.3.3
     Git commit (client): 39fa2fa/1.3.2
     OS/Arch (client): linux/amd64
     Server version: 1.3.2
     Server API version: 1.15
     Go version (server): go1.3.3
     Git commit (server): 39fa2fa/1.3.2

簡単でした。