跨主机网络：实现Docker容器多主机通信
Flannel是CoreOS维护的一个网络组件，在每个主机上运行守护 进程负责维护本地路由转发，Flannel使用ETCD来存储容器网络 与主机之前的关系。
其他主流容器跨主机网络方案：
• Weave
• Calico
• OpenvSwitch
1、etcd安装并配置（任意找一台节点安装即可）
yum -y install etcd
vim /etc/etcd/etcd.conf
ETCD_DATA_DIR="/var/lib/etcd/default.etcd"
ETCD_LISTEN_CLIENT_URLS="http://192.168.0.11:2379"
ETCD_NAME="default"
ETCD_ADVERTISE_CLIENT_URLS="http://192.168.0.11:2379"
systemctl start etcd
systemctl enable etcd
ss -anpt |grep 2379
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2、flanneld安装并配置（两台跨主机的docker主机安装）
yum -y install flannel
vim /etc/sysconfig/flanneld
FLANNEL_ETCD_ENDPOINTS="http://192.168.0.11:2379"
FLANNEL_ETCD_PREFIX="/atomic.io/network"
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3、向etcd写入子网启动并flanneld服务
etcdctl --endpoints="http://192.168.0.11:2379" set /atomic.io/network/config '{ "Network":"172.17.0.0/16", "Backend": {"Type": "vxlan"}} '
etcdctl --endpoints="http://192.168.0.11:2379" get /atomic.io/network/config
systemctl start flanneld.service
systemctl enable flanneld.service
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4、配置Docker使用flannel生成的网络信息 (两台跨主机的docker主机配置）
vim /usr/lib/systemd/system/docker.service
EnvironmentFile=/var/run/flannel/docker
ExecStart=/usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock $DOCKER_NETWORK_OPTIONS
systemctl daemon-reload
systemctl restart docker
ps -ef |grep docker
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5.两台跨主机的docker主机设置iptable转发策略为允许并重启服务（按顺序启动）
iptables -P FORWARD ACCEPT
systemctl restart flanneld.service
systemctl restart docker.service
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6、在两台主机创建容器相互ping验证
docker run -it busybox sh
ifconfig
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防火墙学习：
https://www.cnblogs.com/shijiaqi1066/p/3812510.html
http://www.zsythink.net/archives/1199
