docker自带api接口，需要手动开启。

这里是yum安装的docker，版本是1.12

[root@localhost ~]# vi /lib/systemd/system/docker.service
ExecStart=/usr/bin/dockerd-current \
 --add-runtime docker-runc=/usr/libexec/docker/docker-runc-current \
 --default-runtime=docker-runc \
 --exec-opt native.cgroupdriver=systemd \
 --userland-proxy-path=/usr/libexec/docker/docker-proxy-current \
 $OPTIONS \
 $DOCKER_STORAGE_OPTIONS \
 $DOCKER_NETWORK_OPTIONS \
 $ADD_REGISTRY \
 $BLOCK_REGISTRY \
 $INSECURE_REGISTRY\
 $REGISTRIES\ # 不要忘记此换行
 -H unix:///var/run/docker.sock -H tcp://0.0.0.0:2222 # 添加的

# 重启docker服务
[root@localhost ~]# service docker restart
Redirecting to /bin/systemctl restart docker.service
Warning: docker.service changed on disk. Run ‘systemctl daemon-reload’ to reload units.

# 提示先执行 systemctl daemon-reload
[root@localhost ~]# systemctl daemon-reload
[root@localhost ~]# service docker restart
Redirecting to /bin/systemctl restart docker.service
[root@localhost ~]# netstat -tnlp | grep 2222
tcp6 0 0 :::2222 :::* LISTEN 5750/dockerd-curren