一介绍
flannel是CoreOS提供用于解决Dokcer集群跨主机通讯的覆盖网络工具。它的主要思路是：预先留出一个网段，每个主机使用其中一部分，然后每个容器被分配不同的ip；
让所有的容器认为大家在同一个直连的网络，底层通过UDP/VxLAN等进行报文的封装和转发。
flannel是Overlay网络的一种，也是将源数据包封装在另一种网络包里面进行路由转发和通信，目前已经支持UDP,VXLAN,host-gw,AWS,VPC,GCE路由等级传输,推荐 vxlan或者host-gw
二搭建（这里以两台为例）
2.1 分配网段，封装类型为vxlan,高效，稳定（master上执行）
etcdctl --ca-file=/etc/etcd/ssl/etcd-root-ca.pem --cert-file=/etc/etcd/ssl/etcd.pem --key-file=/etc/etcd/ssl/etcd-key.pem \
--endpoints=https://192.168.137.66:2379,https://192.168.137.16:2379 set /coreos.com/network/config '{ "Network": "172.17.0.0/16", "Backend": {"Type": "vxlan"}}
查看分配的结果：
[root@k8s-master ~]# etcdctl --ca-file=/etc/etcd/ssl/etcd-root-ca.pem --cert-file=/etc/etcd/ssl/etcd.pem --key-file=/etc/etcd/ssl/etcd-key.pem \
--endpoints=https://192.168.137.66:2379,https://192.168.137.16:2379 get /coreos.com/network/config '{ "Network": "172.17.0.0/16", "Backend": {"Type": "vxlan"}}' { "Network": "172.17.0.0/16", "Backend": {"Type": "vxlan"}}
2.2 下载并安装(master上执行)
mkdir /home/softs
cd /home/softs
wget https://github.com/coreos/flannel/releases/download/v0.11.0/flannel-v0.11.0-linux-amd64.tar.gz
tar xf flannel-v0.11.0-linux-amd64.tar.gz
mv flanneld mk-docker-opts.sh /opt/kubernetes/bin/
[root@k8s-master softs]# cat flanneld.sh #这里我们继续使用上一篇中安装etcd时生成的pem证书 #!/bin/bash ETCD_ENDPOINTS=${1:-"http://127.0.0.1:2379"} cat <<EOF >/opt/kubernetes/cfg/flanneld FLANNEL_OPTIONS="--etcd-endpoints=${ETCD_ENDPOINTS} \ -etcd-cafile=/etc/etcd/ssl/etcd-root-ca.pem \ -etcd-certfile=/etc/etcd/ssl/etcd.pem \ -etcd-keyfile=/etc/etcd/ssl/etcd-key.pem" EOF cat <<EOF >/usr/lib/systemd/system/flanneld.service [Unit] Description=Flanneld overlay address etcd agent After=network-online.target network.target Before=docker.service [Service] Type=notify EnvironmentFile=/opt/kubernetes/cfg/flanneld ExecStart=/opt/kubernetes/bin/flanneld --ip-masq \$FLANNEL_OPTIONS ExecStartPost=/opt/kubernetes/bin/mk-docker-opts.sh -k DOCKER_NETWORK_OPTIONS -d /run/flannel/subnet.env Restart=on-failure [Install] WantedBy=multi-user.target EOF cat <<EOF >/usr/lib/systemd/system/docker.service [Unit] Description=Docker Application Container Engine Documentation=https://docs.docker.com After=network-online.target firewalld.service Wants=network-online.target [Service] Type=notify EnvironmentFile=/run/flannel/subnet.env ExecStart=/usr/bin/dockerd \$DOCKER_NETWORK_OPTIONS ExecReload=/bin/kill -s HUP \$MAINPID LimitNOFILE=infinity LimitNPROC=infinity LimitCORE=infinity TimeoutStartSec=0 Delegate=yes KillMode=process Restart=on-failure StartLimitBurst=3 StartLimitInterval=60s [Install] WantedBy=multi-user.target EOF systemctl daemon-reload systemctl enable flanneld systemctl restart flanneld systemctl restart docker
sh -x flanneld.sh https://192.168.137.66:2379,https://192.168.137.16:2379
分发到节点上执行（master 上执行）
cd /home/softs
scp flanneld.sh root@k8s-node1:/home/softs/
cd /opt/kubernetes/bin/
scp flanneld mk-docker-opts.sh root@master-node1:/opt/kubernetes/bin/
节点上执行（各节点执行）
sh -x flanneld.sh https://192.168.137.66:2379,https://192.168.137.16:2379
2.3 查看flannel状态（都可查看）
[root@k8s-master softs]# etcdctl --ca-file=/etc/etcd/ssl/etcd-root-ca.pem --cert-file=/etc/etcd/ssl/etcd.pem --key-file=/etc/etcd/ssl/etcd-key.pem \
--endpoints="https://192.168.137.66:2379,https://192.168.137.16:2379" ls /coreos.com/network/subnets /coreos.com/network/subnets/172.17.90.0-24 /coreos.com/network/subnets/172.17.84.0-24
[root@k8s-master softs]# etcdctl --ca-file=/etc/etcd/ssl/etcd-root-ca.pem --cert-file=/etc/etcd/ssl/etcd.pem --key-file=/etc/etcd/ssl/etcd-key.pem \
--endpoints="https://192.168.137.66:2379,https://192.168.137.16:2379" get /coreos.com/network/subnets/172.17.84.0-24 docker
{"PublicIP":"192.168.137.16","BackendType":"vxlan","BackendData":{"VtepMAC":"76:ec:3f:7c:1b:81"}}
[root@k8s-master softs]# etcdctl --ca-file=/etc/etcd/ssl/etcd-root-ca.pem --cert-file=/etc/etcd/ssl/etcd.pem --key-file=/etc/etcd/ssl/etcd-key.pem \
--endpoints="https://192.168.137.66:2379,https://192.168.137.16:2379" get /coreos.com/network/subnets/172.17.90.0-24 docker
{"PublicIP":"192.168.137.66","BackendType":"vxlan","BackendData":{"VtepMAC":"9e:51:aa:45:24:7f"}}
查看路由情况
#master
[root@k8s-master bin]# route -n Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 0.0.0.0 192.168.137.1 0.0.0.0 UG 100 0 0 ens33 172.17.84.0 172.17.84.0 255.255.255.0 UG 0 0 0 flannel.1 172.17.90.0 0.0.0.0 255.255.255.0 U 0 0 0 docker0 192.168.137.0 0.0.0.0 255.255.255.0 U 100 0 0 ens33
#node
[root@k8s-node1 softs]# route -n Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 0.0.0.0 192.168.137.1 0.0.0.0 UG 100 0 0 ens33 172.17.84.0 0.0.0.0 255.255.255.0 U 0 0 0 docker0 172.17.90.0 172.17.90.0 255.255.255.0 UG 0 0 0 flannel.1 192.168.137.0 0.0.0.0 255.255.255.0 U 100 0 0 ens33