手动搭建k8s-1.16.6高可用集群之部署flannel网络

kubernetes 要求集群内各节点(包括 master 节点)能通过 Pod 网段互联互通。flannel 使用 vxlan 技术为各节点创建一个可以互通的 Pod 网络，使用的端口为 UDP 8472（需要开放该端口，如公有云 AWS 等）。

flanneld 第一次启动时，从 etcd 获取配置的 Pod 网段信息，为本节点分配一个未使用的地址段，然后创建 flannedl.1 网络接口（也可能是其它名称，如 flannel1 等）。

flannel 将分配给自己的 Pod 网段信息写入 /run/flannel/docker 文件，docker 后续使用这个文件中的环境变量设置 docker0 网桥，从而从这个地址段为本节点的所有 Pod 容器分配 IP。

注意：

1、如果没有特殊指明，本文档的所有操作均在 k8s-01 节点上执行，然后远程分发文件和执行命令；

2、flanneld 与 etcd v3.4.x不兼容，需要保证安装的 etcd 为 v3.3.x；

3、flanneld 与 docker 结合使用；

一、下载和分发flanneld二进制文件

cd /opt/k8s/work
mkdir flannel
wget https://github.com/coreos/flannel/releases/download/v0.11.0/flannel-v0.11.0-linux-amd64.tar.gz
tar -zxf flannel-v0.11.0-linux-amd64.tar.gz -C flannel

分发二进制文件到集群所有节点：

cat > deploy.sh << "EOF"
#!/bin/bash
cd /opt/k8s/work
source /opt/k8s/bin/environment.sh 
for node_ip in ${NODE_IPS[@]}
do
    echo ">>> ${node_ip}"
    scp flannel/{flanneld,mk-docker-opts.sh} root@${node_ip}:/opt/k8s/bin/
    ssh root@${node_ip} "chmod +x /opt/k8s/bin/*"
done
EOF

二、创建flannel证书和私钥

flanneld 从 etcd 集群存取网段分配信息，而 etcd 集群启用了双向 x509 证书认证，所以需要为 flanneld 生成证书和私钥。

创建证书签名请求：

cd /opt/k8s/work

cat > flanneld-csr.json <<EOF
{
  "CN": "flanneld",
  "hosts": [],
  "key": {
    "algo": "rsa",
    "size": 2048
  },
  "names": [
    {
      "C": "CN",
      "ST": "BeiJing",
      "L": "BeiJing",
      "O": "k8s",
      "OU": "4Paradigm"
    }
  ]
}
EOF

• 该证书只会被 kubectl 当做 client 证书使用，所以 hosts 字段为空；

生成证书和私钥：

$ cfssl gencert -ca=/opt/k8s/work/ca.pem \
  -ca-key=/opt/k8s/work/ca-key.pem \
  -config=/opt/k8s/work/ca-config.json \
  -profile=kubernetes flanneld-csr.json | cfssljson -bare flanneld
  
$ ls flanneld*pem
flanneld-key.pem  flanneld.pem

将生成的证书和私钥分发到所有节点（master 和 worker）：

cat > deploy.sh << "EOF"
#!/bin/bash
cd /opt/k8s/work
source /opt/k8s/bin/environment.sh 
for node_ip in ${NODE_IPS[@]}
do
    echo ">>> ${node_ip}"
    ssh root@${node_ip} "mkdir -p /etc/flanneld/cert"
    scp flanneld*.pem root@${node_ip}:/etc/flanneld/cert
done
EOF

三、向etcd写入集群Pod网段信息

注意：本步骤只需执行一次。

$ cd /opt/k8s/work
$ source /opt/k8s/bin/environment.sh

$ etcdctl \
  --endpoints=${ETCD_ENDPOINTS} \
  --ca-file=/opt/k8s/work/ca.pem \
  --cert-file=/opt/k8s/work/flanneld.pem \
  --key-file=/opt/k8s/work/flanneld-key.pem \
  mk ${FLANNEL_ETCD_PREFIX}/config '{"Network":"'${CLUSTER_CIDR}'", "SubnetLen": 21, "Backend": {"Type": "vxlan"}}'

• flanneld 当前版本 (v0.11.0) 不支持 etcd v3，故使用 etcd v2 API 写入配置 key 和网段数据；
• 写入的 Pod 网段 ${CLUSTER_CIDR} 地址段（如 /16）必须小于 SubnetLen，必须与 kube-controller-manager 的 --cluster-cidr 参数值一致；

四、创建 flanneld 的 systemd unit 文件

$ cd /opt/k8s/work
$ source /opt/k8s/bin/environment.sh

$ cat > flanneld.service << EOF
[Unit]
Description=Flanneld overlay address etcd agent
After=network.target
After=network-online.target
Wants=network-online.target
After=etcd.service
Before=docker.service

[Service]
Type=notify
ExecStart=/opt/k8s/bin/flanneld \\
  -etcd-cafile=/etc/kubernetes/cert/ca.pem \\
  -etcd-certfile=/etc/flanneld/cert/flanneld.pem \\
  -etcd-keyfile=/etc/flanneld/cert/flanneld-key.pem \\
  -etcd-endpoints=${ETCD_ENDPOINTS} \\
  -etcd-prefix=${FLANNEL_ETCD_PREFIX} \\
  -iface=${IFACE} \\
  -ip-masq
ExecStartPost=/opt/k8s/bin/mk-docker-opts.sh -k DOCKER_NETWORK_OPTIONS -d /run/flannel/docker
Restart=always
RestartSec=5
StartLimitInterval=0

[Install]
WantedBy=multi-user.target
RequiredBy=docker.service
EOF

• mk-docker-opts.sh 脚本将分配给 flanneld 的 Pod 子网段信息写入 /run/flannel/docker 文件，后续 docker 启动时使用这个文件中的环境变量配置 docker0 网桥；
• flanneld 使用系统缺省路由所在的接口与其它节点通信，对于有多个网络接口（如内网和公网）的节点，可以用 -iface 参数指定通信接口;
• flanneld 运行时需要 root 权限；
• -ip-masq: flanneld 为访问 Pod 网络外的流量设置 SNAT 规则，同时将传递给 Docker 的变量 --ip-masq（/run/flannel/docker 文件中）设置为 false，这样 Docker 将不再创建 SNAT 规则； Docker 的 --ip-masq 为 true 时，创建的 SNAT 规则比较“暴力”：将所有本节点 Pod 发起的、访问非 docker0 接口的请求做 SNAT，这样访问其他节点 Pod 的请求来源 IP 会被设置为 flannel.1 接口的 IP，导致目的 Pod 看不到真实的来源 Pod IP。 flanneld 创建的 SNAT 规则比较温和，只对访问非 Pod 网段的请求做 SNAT。

五、分发 flanneld systemd unit文件到所有节点

cat > deploy.sh << "EOF"
#!/bin/bash
cd /opt/k8s/work
source /opt/k8s/bin/environment.sh 
for node_ip in ${NODE_IPS[@]}
do
    echo ">>> ${node_ip}"
    scp flanneld.service root@${node_ip}:/etc/systemd/system/
done
EOF

六、启动flanneld服务

cat > deploy.sh << "EOF"
#!/bin/bash
cd /opt/k8s/work
source /opt/k8s/bin/environment.sh 
for node_ip in ${NODE_IPS[@]}
do
    echo ">>> ${node_ip}"
    ssh root@${node_ip} "systemctl daemon-reload && systemctl enable flanneld && systemctl restart flanneld"
done
EOF

七、检查启动结果

cat > deploy.sh << "EOF"
#!/bin/bash
cd /opt/k8s/work
source /opt/k8s/bin/environment.sh 
for node_ip in ${NODE_IPS[@]}
do
    echo ">>> ${node_ip}"
    ssh root@${node_ip} "systemctl status flanneld|grep Active"
done
EOF

输出结果如下：

$ ./deploy.sh 
>>> 192.168.0.71
   Active: active (running) since Thu 2020-04-23 14:10:55 CST; 5min ago
>>> 192.168.0.72
   Active: active (running) since Thu 2020-04-23 14:10:57 CST; 5min ago
>>> 192.168.0.73
   Active: active (running) since Thu 2020-04-23 14:10:58 CST; 5min ago

看到状态为 active (running)，表示启动成功。如果失败，用下面的命令查看日志：

journalctl -u flanneld

八、查看分配给各flanneld的Pod网段信息

查看集群 Pod 网段(/16)：

$ source /opt/k8s/bin/environment.sh

$ etcdctl \
  --endpoints=${ETCD_ENDPOINTS} \
  --ca-file=/etc/kubernetes/cert/ca.pem \
  --cert-file=/etc/flanneld/cert/flanneld.pem \
  --key-file=/etc/flanneld/cert/flanneld-key.pem \
  get ${FLANNEL_ETCD_PREFIX}/config

输出：

{"Network":"172.30.0.0/16", "SubnetLen": 21, "Backend": {"Type": "vxlan"}}

查看已经分配的 Pod 子网段列表(/21)：

$ source /opt/k8s/bin/environment.sh

$ etcdctl \
  --endpoints=${ETCD_ENDPOINTS} \
  --ca-file=/etc/kubernetes/cert/ca.pem \
  --cert-file=/etc/flanneld/cert/flanneld.pem \
  --key-file=/etc/flanneld/cert/flanneld-key.pem \
  ls ${FLANNEL_ETCD_PREFIX}/subnets

输出（结果视部署情况而定）：

/subnets/172.30.128.0-21
/subnets/172.30.88.0-21
/subnets/172.30.104.0-21

查看某一 Pod 网段对应的节点 IP 和 flannel 接口地址:

$ source /opt/k8s/bin/environment.sh

$ etcdctl \
  --endpoints=${ETCD_ENDPOINTS} \
  --ca-file=/etc/kubernetes/cert/ca.pem \
  --cert-file=/etc/flanneld/cert/flanneld.pem \
  --key-file=/etc/flanneld/cert/flanneld-key.pem \
  get ${FLANNEL_ETCD_PREFIX}/subnets/172.30.128.0-21

输出（结果视部署情况而定）：

{"PublicIP":"192.168.0.71","BackendType":"vxlan","BackendData":{"VtepMAC":"e2:5f:51:da:76:54"}}

• 172.30.128.0/21 被分配给节点 k8s-01（192.168.0.71）；
• VtepMAC 为 k8s-01 节点的 flannel.1 网卡 MAC 地址；

九、检查节点 flannel 网络信息

$ ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 00:0c:29:e7:5d:81 brd ff:ff:ff:ff:ff:ff
    inet 192.168.0.71/24 brd 192.168.0.255 scope global noprefixroute eth0
       valid_lft forever preferred_lft forever
3: flannel.1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc noqueue state UNKNOWN group default 
    link/ether e2:5f:51:da:76:54 brd ff:ff:ff:ff:ff:ff
    inet 172.30.128.0/32 scope global flannel.1
       valid_lft forever preferred_lft forever

• flannel.1 网卡的地址为分配的 Pod 子网段的第一个 IP（.0），且是 /32 的地址；

$ ip route show | grep flannel.1
172.30.88.0/21 via 172.30.88.0 dev flannel.1 onlink 
172.30.104.0/21 via 172.30.104.0 dev flannel.1 onlink 

• 到其它节点 Pod 网段请求都被转发到 flannel.1 网卡；
• flanneld 根据 etcd 中子网段的信息，如 ${FLANNEL_ETCD_PREFIX}/subnets/172.30.128.0-24 ，来决定进请求发送给哪个节点的互联 IP；

十、验证各节点能通过 Pod 网段互通

在各节点上部署 flannel 后，检查是否创建了 flannel 接口(名称可能为 flannel0、flannel.0、flannel.1 等)：

cat > deploy.sh << "EOF"
#!/bin/bash
cd /opt/k8s/work
source /opt/k8s/bin/environment.sh 
for node_ip in ${NODE_IPS[@]}
do
    echo ">>> ${node_ip}"
    ssh ${node_ip} "/usr/sbin/ip addr show flannel.1|grep -w inet"
done
EOF

输出：

>>> 192.168.0.71
    inet 172.30.128.0/32 scope global flannel.1
>>> 192.168.0.72
    inet 172.30.88.0/32 scope global flannel.1
>>> 192.168.0.73
    inet 172.30.104.0/32 scope global flannel.1

在各节点上 ping 所有flannel 接口 IP，确保能通：

注意：把其中的IP段换成自己环境的。

cat > deploy.sh << "EOF"
#!/bin/bash
cd /opt/k8s/work
source /opt/k8s/bin/environment.sh 
for node_ip in ${NODE_IPS[@]}
do
    echo ">>> ${node_ip}"
    ssh ${node_ip} "ping -c 1 172.30.128.0"
    ssh ${node_ip} "ping -c 1 172.30.88.0"
    ssh ${node_ip} "ping -c 1 172.30.104.0"
done
EOF

输出：

$ ./deploy.sh 
>>> 192.168.0.71
PING 172.30.128.0 (172.30.128.0) 56(84) bytes of data.
64 bytes from 172.30.128.0: icmp_seq=1 ttl=64 time=0.073 ms

--- 172.30.128.0 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.073/0.073/0.073/0.000 ms
PING 172.30.88.0 (172.30.88.0) 56(84) bytes of data.
64 bytes from 172.30.88.0: icmp_seq=1 ttl=64 time=0.427 ms

--- 172.30.88.0 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.427/0.427/0.427/0.000 ms
PING 172.30.104.0 (172.30.104.0) 56(84) bytes of data.
64 bytes from 172.30.104.0: icmp_seq=1 ttl=64 time=0.507 ms

--- 172.30.104.0 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.507/0.507/0.507/0.000 ms
>>> 192.168.0.72
PING 172.30.128.0 (172.30.128.0) 56(84) bytes of data.
64 bytes from 172.30.128.0: icmp_seq=1 ttl=64 time=0.527 ms

--- 172.30.128.0 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.527/0.527/0.527/0.000 ms
PING 172.30.88.0 (172.30.88.0) 56(84) bytes of data.
64 bytes from 172.30.88.0: icmp_seq=1 ttl=64 time=0.077 ms

--- 172.30.88.0 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.077/0.077/0.077/0.000 ms
PING 172.30.104.0 (172.30.104.0) 56(84) bytes of data.
64 bytes from 172.30.104.0: icmp_seq=1 ttl=64 time=0.468 ms

--- 172.30.104.0 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.468/0.468/0.468/0.000 ms
>>> 192.168.0.73
PING 172.30.128.0 (172.30.128.0) 56(84) bytes of data.
64 bytes from 172.30.128.0: icmp_seq=1 ttl=64 time=0.455 ms

--- 172.30.128.0 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.455/0.455/0.455/0.000 ms
PING 172.30.88.0 (172.30.88.0) 56(84) bytes of data.
64 bytes from 172.30.88.0: icmp_seq=1 ttl=64 time=0.144 ms

--- 172.30.88.0 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.144/0.144/0.144/0.000 ms
PING 172.30.104.0 (172.30.104.0) 56(84) bytes of data.
64 bytes from 172.30.104.0: icmp_seq=1 ttl=64 time=0.047 ms

--- 172.30.104.0 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.047/0.047/0.047/0.000 ms