docker open remote control port

Docker provides a remote control API, which uses the restful style
centos7 opening method:
vim /lib/systemd/system/docker.service
find the ExecStart line and
modify it to

ExecStart=/usr/bin/dockerd -H tcp://0.0.0.0:2375 -H unix:///var/run/docker.sock

restart docker

systemctl daemon-reload
systemctl restart docker