Question

环境：Centos7

1.先检查是否安装旧版本 docker

[root@registry ~]# rpm -qa|grep docker
[root@registry ~]# 
我这里没有安装，如果安装，请 rpm -e 卸载

2.编辑 docker.repo 文件，写入如下内容

[root@registry ~]# vim /etc/yum.repos.d/docker-main.repo
[docker-main-repo]
name=Docker main Repository
baseurl=https://yum.dockerproject.org/repo/main/centos/7 
enabled=1
gpgcheck=1
gpgkey=https://yum.dockerproject.org/gpg 

3.安装 docker

[root@registry ~]# yum install docker-engine

4.关闭防火墙和 selinux

[root@registry ~]# systemctl stop firewalld.service
[root@registry ~]# systemctl disable firewalld.service
[root@registry ~]# vi /etc/selinux/config
修改 /etc/selinux/config 文件中的 SELINUX="" 为 disabled ，然后重启

5.增加 tcp 监听端口

修改 docker 配置文件
[root@registry ~]# vi /lib/systemd/system/docker.service 
ExecStart=/usr/bin/dockerd -H unix:///var/run/docker.sock -D -H  tcp://0.0.0.0:2375 
保存退出

6.启动 docker

[root@registry ~]# systemctl start docker
[root@registry ~]# ps -ef|grep docker
root     20803     1  0 8 月 09 ?       00:06:18 /usr/bin/dockerd -H unix:///var/run/docker.sock -D -H  tcp://0.0.0.0:2375 
root     20809 20803  0 8 月 09 ?       00:00:09 docker-containerd -l unix:///var/run/docker/libcontainerd/docker-containerd.sock --shim docker-containerd-shim --metrics-interval=0 --start-timeout 2m --state-dir /var/run/docker/libcontainerd/containerd --runtime docker-runc --debug
root     31072 22506  0 10:29 pts/7    00:00:00 grep --color=auto docker

7.查看其它 docker 信息

[root@registry ~]# docker -H 192.168.20.112:2375 version
[root@registry ~]# docker -H 192.168.20.112:2375 info
[root@registry ~]# docker -H 192.168.20.112:2375 ps

附：新版 docker 内置 swarm 实现集群 我们安装的是 1.12 版 Docker Engine，Docker Swarm 已经被整合到了 Docker Engine，这样就可以更容易的把多个 Docker 主机组合成一整个规模更大可靠性更高的逻辑单元。

[root@master ~]# docker swarm --help

Usage:  docker swarm COMMAND

Manage Docker Swarm

Options:
      --help   Print usage

Commands:
  init        Initialize a swarm
  join        Join a swarm as a node and/or manager
  join-token  Manage join tokens
  update      Update the swarm
  leave       Leave a swarm

Run 'docker swarm COMMAND --help' for more information on a command.

1)创建 swarm 管理节点

[root@master ~]# docker swarm init --listen-addr 0.0.0.0:2377 --advertise-addr 192.168.20.113
Swarm initialized: current node (79l4eevt1sx63cw8ewb7xf1fh) is now a manager.

To add a worker to this swarm, run the following command:
    docker swarm join \
    --token SWMTKN-1-53zfa8v239nibt9eum4buemmq3wkfjsrqjxbte9ay93i3xzlsn-8cch0txhv5bl9bmlt7jh9gw68 \
    192.168.20.113:2377

To add a manager to this swarm, run the following command:
    docker swarm join \
    --token SWMTKN-1-53zfa8v239nibt9eum4buemmq3wkfjsrqjxbte9ay93i3xzlsn-acsxqva1dj6m1gsjpaa6akhvg \
    192.168.20.113:2377

看以看到管理节点已创建，多了几个监听端口：
TCP 端口 2377 集群管理端口
TCP 与 UDP 端口 7946 节点之间通讯端口

[root@master ~]# docker info
Containers: 9
 Running: 6
 Paused: 0
 Stopped: 3
Images: 22
Server Version: 1.12.0
Storage Driver: devicemapper
 Pool Name: docker-253:0-71406753-pool
 Pool Blocksize: 65.54 kB
 Base Device Size: 10.74 GB
 Backing Filesystem: xfs
 Data file: /dev/loop0
 Metadata file: /dev/loop1
 Data Space Used: 5.277 GB
 Data Space Total: 107.4 GB
 Data Space Available: 7.192 GB
 Metadata Space Used: 9.925 MB
 Metadata Space Total: 2.147 GB
 Metadata Space Available: 2.138 GB
 Thin Pool Minimum Free Space: 10.74 GB
 Udev Sync Supported: true
 Deferred Removal Enabled: false
 Deferred Deletion Enabled: false
 Deferred Deleted Device Count: 0
 Data loop file: /var/lib/docker/devicemapper/devicemapper/data
 WARNING: Usage of loopback devices is strongly discouraged for production use. Use `--storage-opt dm.thinpooldev` to specify a custom block storage device.
 Metadata loop file: /var/lib/docker/devicemapper/devicemapper/metadata
 Library Version: 1.02.107-RHEL7 (2016-06-09)
Logging Driver: json-file
Cgroup Driver: cgroupfs
Plugins:
 Volume: local
 Network: host bridge null overlay
Swarm: active
 NodeID: 79l4eevt1sx63cw8ewb7xf1fh
 Is Manager: true
 ClusterID: a1annjmn8ks1tg6a3n0dqg2s4
 Managers: 1
 Nodes: 1
 Orchestration:
  Task History Retention Limit: 5
 Raft:
  Snapshot interval: 10000
  Heartbeat tick: 1
  Election tick: 3
 Dispatcher:
  Heartbeat period: 5 seconds
 CA configuration:
  Expiry duration: 3 months
 Node Address: 192.168.20.113
Runtimes: runc
Default Runtime: runc
Security Options: seccomp
Kernel Version: 3.10.0-327.el7.x86_64
Operating System: CentOS Linux 7 (Core)
OSType: linux
Architecture: x86_64
CPUs: 1
Total Memory: 1.793 GiB
Name: node1.docker.com
ID: HXUI:TQ3U:RMGP:5Q2W:V4L5:6JDM:4DB6:LEKK:4JBU:GQVP:NV2C:P72Y
Docker Root Dir: /var/lib/docker
Debug Mode (client): false
Debug Mode (server): true
 File Descriptors: 60
 Goroutines: 164
 System Time: 2016-08-13T18:19:06.836430668+08:00
 EventsListeners: 1
Registry:  https://index.docker.io/v1/ 
WARNING: bridge-nf-call-ip6tables is disabled
Insecure Registries:
 192.168.20.113:5000
 127.0.0.0/8

2)添加节点到集群

[root@node1 ~]# docker swarm join \
    --token SWMTKN-1-53zfa8v239nibt9eum4buemmq3wkfjsrqjxbte9ay93i3xzlsn-8cch0txhv5bl9bmlt7jh9gw68 \
    192.168.20.113:2377
This node joined a swarm as a worker.

3)在 manager 节点上查看节点

[root@master ~]# docker node ls
ID                           HOSTNAME          STATUS  AVAILABILITY  MANAGER STATUS
1yid2aeraryzrhcdnmvyze6xq    node2.docker.com  Ready   Active        
79l4eevt1sx63cw8ewb7xf1fh *  node1.docker.com  Ready   Active        Leader

4)常见的双层（web+db）应用可按以下方法创建：

docker network create -d overlay mynet
docker service create --name frontend --replicas 5 -p 80:80/tcp \
--network mynet mywebapp
docker service create --name redis --network mynet redis:latest

以下为此应用的基本架构示意图：

这条命令声明了必要状态，即将由 5 套 Nginx 容器构成的 Swarm 作为单一内部负载均衡型服务，且于 Swarm 内任意节点的端口 80 上进行交付。

Swarm 模式下的引擎拥有自组织与自修复特性，意味着它们能够识别我们定义的应用，并在出现差错时持续检查并修复环境。举例来说，如果大家关闭某台运行有 Nginx 实例的设备，则另一节点上会自动启动一套新的容器。如果关闭 Swarm 内半数设备所使用的网络交换机，则另外一半设备会顶替而上，接管对应工作负载。