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kubernetes需要使用第三方的網路外掛來實現kubernetes的網路功能，這樣一來，安裝網路外掛成為必要前提；第三方網路外掛有多種，常用的有flanneld、calico和cannel（flanneld+calico），不同的網路元件，都提供基本的網路功能，為各個Node節點提供IP網路等。

二進位制下載連結https://github.com/coreos/flannel/releases/download/v0.11.0/flannel-v0.11.0-linux-amd64.tar.gz，下載完成後，分發到所有節點的/data/k8s/bin/目錄下。

Flannel外掛支援三種通訊模式如下

Flanneld配置寫到Etcd中

cd /data/k8s/work
source /data/k8s/bin/env.sh
etcdctl \
  --endpoints=${ETCD_ENDPOINTS} \
  --ca-file=/data/k8s/work/ca.pem \
  --cert-file=/data/k8s/work/flanneld.pem \
  --key-file=/data/k8s/work/flanneld-key.pem \
  mk ${FLANNEL_ETCD_PREFIX}/config '{"Network":"'${CLUSTER_CIDR}'", "SubnetLen": 21, "Backend": {"Type": "vxlan", "DirectRouting": true}}'
 

這裡我們使用VxLan+DirectRouting的模式進行通訊，Node節點網段相同，直接路由，節點網段不同，使用Vxlan進行封裝；

檢視etcd中儲存配置

#!/bin/bash

source /data/k8s/bin/env.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

結果如下：
{"Network":"172.19.0.0/16", "SubnetLen": 21, "Backend": {"Type": "vxlan", "DirectRouting": true}}
 

建立Flanneld啟動檔案並分發

#!/bin/bash

cd /data/k8s/work
source /data/k8s/bin/env.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=/data/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=/data/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

for node_ip in ${NODE_IPS[@]}
do
    echo ">>> ${node_ip}"
    scp flannel

配置詳解

啟動flannel

#!/bin/bash

cd /data/k8s/work
source /data/k8s/bin/env.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

驗證

#!/bin/bash
source /data/k8s/bin/env.sh
for node_ip in ${NODE_IPS[@]}
do
    echo ">>> ${node_ip}"
    ssh root@${node_ip} "systemctl status flanneld|grep -i Active"
done

驗證結果

>>> 192.168.16.104
   Active: active (running) since Sun 2019-12-29 18:03:43 CST; 1 months 0 days ago
>>> 192.168.16.105
   Active: active (running) since Sat 2019-12-28 22:33:27 CST; 1 months 1 days ago
>>> 192.168.16.106
   Active: active (running) since Sat 2019-12-28 22:33:27 CST; 1 months 1 days ago
>>> 192.168.16.107
   Active: active (running) since Sat 2019-12-28 22:33:28 CST; 1 months 1 days ago

檢視已分配的網段資訊

#!/bin/bash

source /data/k8s/bin/env.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

結果如下：
/kubernetes/network/subnets/172.19.120.0-21
/kubernetes/network/subnets/172.19.184.0-21
/kubernetes/network/subnets/172.19.72.0-21
/kubernetes/network/subnets/172.19.56.0-21

檢視下分配網段的詳情：

#!/bin/bash

source /data/k8s/bin/env.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/172.19.120.0-21

結果如下：
{"PublicIP":"192.168.16.104","BackendType":"vxlan","BackendData":{"VtepMAC":"aa:ea:b2:e1:88:a5"}}

總結

網路外掛有多種，根據公司或個人實際情況進行選擇，網上很多前輩說flannel支援的網路規模受限，建議使用calico，由於測試環境規模不大，這裡使用flannel即可滿足。