Overlay 网络是指在不改变现有网络基础设施的前提下，通过某种约定通信协议，把二层报文封装在 IP 报文之上的新的数据格式。这样不但能够充分利用成熟的 IP 路由协议进程数据分发；而且在 Overlay 技术中采用扩展的隔离标识位数，能够突破 VLAN 的 4000 数量限制支持高达 16M 的用户，并在必要时可将广播流量转化为组播流量，避免广播数据泛滥。
因此，Overlay 网络实际上是目前最主流的容器跨节点数据传输和路由方案。
Flannel 是 CoreOS 团队针对 Kubernetes 设计的一个覆盖网络（Overlay Network）工具，其目的在于帮助每一个使用 Kuberentes 的 CoreOS 主机拥有一个完整的子网。 Flannel 通过给每台宿主机分配一个子网的方式为容器提供虚拟网络，它基于 Linux TUN/TAP，使用 UDP 封装 IP 包来创建 overlay 网络，并借助 etcd 维护网络的分配情况。 Flannel is a simple and easy way to configure a layer 3 network fabric designed for Kubernetes.
Flannel 是 CoreOS 团队针对 Kubernetes 设计的一个网络规划服务，简单来说，它的功能是让集群中的不同节点主机创建的 Docker 容器都具有全集群唯一的虚拟 IP 地址。但在默认的 Docker 配置中，每个 Node 的 Docker 服务会分别负责所在节点容器的 IP 分配。Node 内部的容器之间可以相互访问,但是跨主机 (Node) 网络相互间是不能通信。Flannel 设计目的就是为集群中所有节点重新规划 IP 地址的使用规则，从而使得不同节点上的容器能够获得 " 同属一个内网 " 且 " 不重复的 “IP 地址，并让属于不同节点上的容器能够直接通过内网 IP 通信。 Flannel 使用 etcd 存储配置数据和子网分配信息。flannel 启动之后，后台进程首先检索配置和正在使用的子网列表，然后选择一个可用的子网，然后尝试去注册它。etcd 也存储这个每个主机对应的 ip。flannel 使用 etcd 的 watch 机制监视 /coreos.com/network/subnets 下面所有元素的变化信息，并且根据它来维护一个路由表。为了提高性能，flannel 优化了 Universal TAP/TUN 设备，对 TUN 和 UDP 之间的 ip 分片做了代理。 如下原理图：
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| 1、数据从源容器中发出后，经由所在主机的docker0虚拟网卡转发到flannel0虚拟网卡，这是个P2P的虚拟网卡，flanneld服务监听在网卡的另外一端。
2、Flannel通过Etcd服务维护了一张节点间的路由表，该张表里保存了各个节点主机的子网网段信息。
3、源主机的flanneld服务将原本的数据内容UDP封装后根据自己的路由表投递给目的节点的flanneld服务，数据到达以后被解包，然后直接进入目的节点的flannel0虚拟网卡，然后被转发到目的主机的docker0虚拟网卡，最后就像本机容器通信一样的由docker0路由到达目标容器。
|
etcd 是 CoreOS 团队于 2013 年 6 月发起的开源项目，它的目标是构建一个高可用的分布式键值 (key-value) 数据库。etcd 内部采用 raft 协议作为一致性算法，etcd 基于 Go 语言实现。
etcd 作为服务发现系统，特点：
- 简单：安装配置简单，而且提供了 HTTP API 进行交互，使用也很简单
- 安全：支持 SSL 证书验证
- 快速：根据官方提供的 benchmark 数据，单实例支持每秒 2k+ 读操作
- 可靠：采用 raft 算法，实现分布式系统数据的可用性和一致性
主机防火墙及 SELINUX 均关闭。
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| # hostnamectl set-hostname node1
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| # hostnamectl set-hostname node2
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| # vim /etc/sysconfig/network-scripts/ifcfg-ens33
# cat /etc/sysconfig/network-scripts/ifcfg-ens33
TYPE="Ethernet"
PROXY_METHOD="none"
BROWSER_ONLY="no"
BOOTPROTO="none"
DEFROUTE="yes"
IPV4_FAILURE_FATAL="no"
IPV6INIT="yes"
IPV6_AUTOCONF="yes"
IPV6_DEFROUTE="yes"
IPV6_FAILURE_FATAL="no"
IPV6_ADDR_GEN_MODE="stable-privacy"
NAME="ens33"
UUID="6c020cf7-4c6e-4276-9aa6-0661670da705"
DEVICE="ens33"
ONBOOT="yes"
IPADDR="192.168.255.154"
PREFIX="24"
GATEWAY="192.168.255.2"
DNS1="119.29.29.29"
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| # vim /etc/sysconfig/network-scripts/ifcfg-ens33
# cat /etc/sysconfig/network-scripts/ifcfg-ens33
TYPE="Ethernet"
PROXY_METHOD="none"
BROWSER_ONLY="no"
BOOTPROTO="none"
DEFROUTE="yes"
IPV4_FAILURE_FATAL="no"
IPV6INIT="yes"
IPV6_AUTOCONF="yes"
IPV6_DEFROUTE="yes"
IPV6_FAILURE_FATAL="no"
IPV6_ADDR_GEN_MODE="stable-privacy"
NAME="ens33"
UUID="6c020cf7-4c6e-4276-9aa6-0661670da705"
DEVICE="ens33"
ONBOOT="yes"
IPADDR="192.168.255.155"
PREFIX="24"
GATEWAY="192.168.255.2"
DNS1="119.29.29.29"
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| # vim /etc/hosts
[root@node1 ~]# cat /etc/hosts
127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4
::1 localhost localhost.localdomain localhost6 localhost6.localdomain6
192.168.255.154 node1
192.168.255.155 node2
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| # vim /etc/hosts
[root@node2 ~]# cat /etc/hosts
127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4
::1 localhost localhost.localdomain localhost6 localhost6.localdomain6
192.168.255.154 node1
192.168.255.155 node2
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所有 Docker Host
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| # vim /etc/sysctl.conf
[root@node1 ~]# cat /etc/sysctl.conf
......
net.ipv4.ip_forward=1
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| # vim /etc/sysctl.conf
[root@node2 ~]# cat /etc/sysctl.conf
......
net.ipv4.ip_forward=1
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etcd 集群
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| [root@node1 ~]# yum -y install etcd
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| [root@node2 ~]# yum -y install etcd
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| # vim /etc/etcd/etcd.conf
[root@node1 ~]# cat /etc/etcd/etcd.conf
#[Member]
#ETCD_CORS=""
ETCD_DATA_DIR="/var/lib/etcd/node1.etcd"
#ETCD_WAL_DIR=""
ETCD_LISTEN_PEER_URLS="http://0.0.0.0:2380"
ETCD_LISTEN_CLIENT_URLS="http://0.0.0.0:2379,http://0.0.0.0:4001"
#ETCD_MAX_SNAPSHOTS="5"
#ETCD_MAX_WALS="5"
ETCD_NAME="node1"
#ETCD_SNAPSHOT_COUNT="100000"
#ETCD_HEARTBEAT_INTERVAL="100"
#ETCD_ELECTION_TIMEOUT="1000"
#ETCD_QUOTA_BACKEND_BYTES="0"
#ETCD_MAX_REQUEST_BYTES="1572864"
#ETCD_GRPC_KEEPALIVE_MIN_TIME="5s"
#ETCD_GRPC_KEEPALIVE_INTERVAL="2h0m0s"
#ETCD_GRPC_KEEPALIVE_TIMEOUT="20s"
#
#[Clustering]
ETCD_INITIAL_ADVERTISE_PEER_URLS="http://192.168.255.154:2380"
ETCD_ADVERTISE_CLIENT_URLS="http://192.168.255.154:2379,http://192.168.255.155:4001"
#ETCD_DISCOVERY=""
#ETCD_DISCOVERY_FALLBACK="proxy"
#ETCD_DISCOVERY_PROXY=""
#ETCD_DISCOVERY_SRV=""
ETCD_INITIAL_CLUSTER="node1=http://192.168.255.154:2380,node2=http://192.168.255.155:2380"
#ETCD_INITIAL_CLUSTER_TOKEN="etcd-cluster"
#ETCD_INITIAL_CLUSTER_STATE="new"
#ETCD_STRICT_RECONFIG_CHECK="true"
#ETCD_ENABLE_V2="true"
#
#[Proxy]
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| # vim /etc/etcd/etcd.conf
[root@node2 ~]# cat /etc/etcd/etcd.conf
#[Member]
#ETCD_CORS=""
ETCD_DATA_DIR="/var/lib/etcd/node2.etcd"
#ETCD_WAL_DIR=""
ETCD_LISTEN_PEER_URLS="http://0.0.0.0:2380"
ETCD_LISTEN_CLIENT_URLS="http://0.0.0.0:2379,http://0.0.0.0:4001"
#ETCD_MAX_SNAPSHOTS="5"
#ETCD_MAX_WALS="5"
ETCD_NAME="node2"
#ETCD_SNAPSHOT_COUNT="100000"
#ETCD_HEARTBEAT_INTERVAL="100"
#ETCD_ELECTION_TIMEOUT="1000"
#ETCD_QUOTA_BACKEND_BYTES="0"
#ETCD_MAX_REQUEST_BYTES="1572864"
#ETCD_GRPC_KEEPALIVE_MIN_TIME="5s"
#ETCD_GRPC_KEEPALIVE_INTERVAL="2h0m0s"
#ETCD_GRPC_KEEPALIVE_TIMEOUT="20s"
#
#[Clustering]
ETCD_INITIAL_ADVERTISE_PEER_URLS="http://192.168.255.155:2380"
ETCD_ADVERTISE_CLIENT_URLS="http://192.168.255.155:2379,http://192.168.255.155:4001"
#ETCD_DISCOVERY=""
#ETCD_DISCOVERY_FALLBACK="proxy"
#ETCD_DISCOVERY_PROXY=""
#ETCD_DISCOVERY_SRV=""
ETCD_INITIAL_CLUSTER="node1=http://192.168.255.154:2380,node2=http://192.168.255.155:2380"
#ETCD_INITIAL_CLUSTER_TOKEN="etcd-cluster"
#ETCD_INITIAL_CLUSTER_STATE="new"
#ETCD_STRICT_RECONFIG_CHECK="true"
#ETCD_ENABLE_V2="true"
#
#[Proxy]
|
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| [root@node1 ~]# systemctl enable etcd
[root@node1 ~]# systemctl start etcd
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| [root@node2 ~]# systemctl enable etcd
[root@node2 ~]# systemctl start etcd
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| # netstat -tnlp | grep -E "4001|2380"
|
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| 输出结果：
tcp6 0 0 :::2380 :::* LISTEN 65318/etcd
tcp6 0 0 :::4001 :::* LISTEN 65318/etcd
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| # etcdctl -C http://192.168.255.154:2379 cluster-health
|
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| 输出：
member 5be09658727c5574 is healthy: got healthy result from http://192.168.255.154:2379
member c48e6c7a65e5ca43 is healthy: got healthy result from http://192.168.255.155:2379
cluster is healthy
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| 输出：
5be09658727c5574: name=node1 peerURLs=http://192.168.255.154:2380 clientURLs=http://192.168.255.154:2379,http://192.168.255.155:4001 isLeader=true
c48e6c7a65e5ca43: name=node2 peerURLs=http://192.168.255.155:2380 clientURLs=http://192.168.255.155:2379,http://192.168.255.155:4001 isLeader=false
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| [root@node1 ~]# yum -y install flannel
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| [root@node2 ~]# yum -y install flannel
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| [root@node1 ~]# vim /etc/sysconfig/flanneld
[root@node1 ~]# cat /etc/sysconfig/flanneld
# Flanneld configuration options
# etcd url location. Point this to the server where etcd runs
FLANNEL_ETCD_ENDPOINTS="http://192.168.255.154:2379,http://192.168.255.155:2379"
# etcd config key. This is the configuration key that flannel queries
# For address range assignment
FLANNEL_ETCD_PREFIX="/atomic.io/network"
# Any additional options that you want to pass
#FLANNEL_OPTIONS=""
FLANNEL_OPTIONS="--logtostderr=false --log_dir=/var/log/ --etcd endpoints=http://192.168.255.154:2379,http://192.168.255.155:2379 --iface=ens33"
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| [root@node2 ~]# vim /etc/sysconfig/flanneld
[root@node2 ~]# cat /etc/sysconfig/flanneld
# Flanneld configuration options
# etcd url location. Point this to the server where etcd runs
FLANNEL_ETCD_ENDPOINTS="http://192.168.255.154:2379,http://192.168.255.155:2379"
# etcd config key. This is the configuration key that flannel queries
# For address range assignment
FLANNEL_ETCD_PREFIX="/atomic.io/network"
# Any additional options that you want to pass
#FLANNEL_OPTIONS=""
FLANNEL_OPTIONS="--logtostderr=false --log_dir=/var/log/ --etcd-endpoints=http://192.168.255.154:2379,http://192.168.255.155:2379 --iface=ens33"
|
Flannel 使用 Etcd 进行配置，来保证多个 Flannel 实例之间的配置一致性，所以需要在 etcd 上进行如下配置（’/http://atomic.io/network/config’ 这个 key 与上面的/etc/sysconfig/flannel 中的配置项 FLANNEL_ETCD_PREFIX 是相对应的，错误的话启动就会出错）
该 ip 网段可以任意设定，随便设定一个网段都可以。容器的 ip 就是根据这个网段进行自动分配的，ip 分配后，容器一般是可以对外联网的（网桥模式，只要 Docker Host 能上网即可。）
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| [root@node1 ~]# etcdctl mk /atomic.io/network/config '{"Network":"172.21.0.0/16"}'
{"Network":"172.21.0.0/16"}
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或
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| [root@node1 ~]# etcdctl set /atomic.io/network/config '{"Network":"172.21.0.0/16"}'
{"Network":"172.21.0.0/16"}
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| [root@node1 ~]# etcdctl get /atomic.io/network/config
{"Network":"172.21.0.0/16"}
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| [root@node1 ~]# systemctl enable flanneld;systemctl start flanneld
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| [root@node2 ~]# systemctl enable flanneld;systemctl start flanneld
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| [root@node1 ~]# ls /run/flannel/
docker subnet.env
[root@node1 ~]# cat /run/flannel/subnet.env
FLANNEL_NETWORK=172.21.0.0/16
FLANNEL_SUBNET=172.21.31.1/24
FLANNEL_MTU=1472
FLANNEL_IPMASQ=false
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| [root@node1 ~]# ip a s
......
5: docker0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default
link/ether 02:42:63:d1:9e:0b brd ff:ff:ff:ff:ff:ff
inet 172.17.0.1/16 brd 172.17.255.255 scope global docker0
valid_lft forever preferred_lft forever
6: flannel0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1472 qdisc pfifo_fast state UNKNOWN group default qlen 500
link/none
inet 172.21.31.0/16 scope global flannel0
valid_lft forever preferred_lft forever
inet6 fe80::edfa:d8b0:3351:4126/64 scope link flags 800
valid_lft forever preferred_lft forever
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| [root@node2 ~]# ls /run/flannel/
docker subnet.env
[root@node2 ~]# cat /run/flannel/subnet.env
FLANNEL_NETWORK=172.21.0.0/16
FLANNEL_SUBNET=172.21.55.1/24
FLANNEL_MTU=1472
FLANNEL_IPMASQ=false
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| [root@node2 ~]# ip a s
......
5: docker0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default
link/ether 02:42:e1:16:68:de brd ff:ff:ff:ff:ff:ff
inet 172.17.0.1/16 brd 172.17.255.255 scope global docker0
valid_lft forever preferred_lft forever
6: flannel0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1472 qdisc pfifo_fast state UNKNOWN group default qlen 500
link/none
inet 172.21.55.0/16 scope global flannel0
valid_lft forever preferred_lft forever
inet6 fe80::f895:9b5a:92b1:78aa/64 scope link flags 800
valid_lft forever preferred_lft forever
|
–bip=172.21.31.1/24 –ip-masq=true –mtu=1472 放置于启动程序后
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| [root@node1 ~]# vim /usr/lib/systemd/system/docker.service
[root@node1 ~]# cat /usr/lib/systemd/system/docker.service
[Unit]
Description=Docker Application Container Engine
Documentation=https://docs.docker.com
After=network-online.target firewalld.service containerd.service
Wants=network-online.target
Requires=docker.socket containerd.service
[Service]
Type=notify
# the default is not to use systemd for cgroups because the delegate issues still
# exists and systemd currently does not support the cgroup feature set required
# for containers run by docker
ExecStart=/usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock --bip=172.21.31.1/24 --ip-masq=true --mtu=1472
ExecReload=/bin/kill -s HUP $MAINPID
TimeoutSec=0
RestartSec=2
Restart=always
# Note that StartLimit* options were moved from "Service" to "Unit" in systemd 229.
# Both the old, and new location are accepted by systemd 229 and up, so using the old location
# to make them work for either version of systemd.
StartLimitBurst=3
# Note that StartLimitInterval was renamed to StartLimitIntervalSec in systemd 230.
# Both the old, and new name are accepted by systemd 230 and up, so using the old name to make
# this option work for either version of systemd.
StartLimitInterval=60s
# Having non-zero Limit*s causes performance problems due to accounting overhead
# in the kernel. We recommend using cgroups to do container-local accounting.
LimitNOFILE=infinity
LimitNPROC=infinity
LimitCORE=infinity
# Comment TasksMax if your systemd version does not support it.
# Only systemd 226 and above support this option.
TasksMax=infinity
# set delegate yes so that systemd does not reset the cgroups of docker containers
Delegate=yes
# kill only the docker process, not all processes in the cgroup
KillMode=process
OOMScoreAdjust=-500
[Install]
WantedBy=multi-user.target
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| [root@node2 ~]# vim /usr/lib/systemd/system/docker.service
[root@node2 ~]# cat /usr/lib/systemd/system/docker.service
[Unit]
Description=Docker Application Container Engine
Documentation=https://docs.docker.com
After=network-online.target firewalld.service containerd.service
Wants=network-online.target
Requires=docker.socket containerd.service
[Service]
Type=notify
# the default is not to use systemd for cgroups because the delegate issues still
# exists and systemd currently does not support the cgroup feature set required
# for containers run by docker
ExecStart=/usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock --bip=172.21.55.1/24 --ip-masq=true --mtu=1472
ExecReload=/bin/kill -s HUP $MAINPID
TimeoutSec=0
RestartSec=2
Restart=always
# Note that StartLimit* options were moved from "Service" to "Unit" in systemd 229.
# Both the old, and new location are accepted by systemd 229 and up, so using the old location
# to make them work for either version of systemd.
StartLimitBurst=3
# Note that StartLimitInterval was renamed to StartLimitIntervalSec in systemd 230.
# Both the old, and new name are accepted by systemd 230 and up, so using the old name to make
# this option work for either version of systemd.
StartLimitInterval=60s
# Having non-zero Limit*s causes performance problems due to accounting overhead
# in the kernel. We recommend using cgroups to do container-local accounting.
LimitNOFILE=infinity
LimitNPROC=infinity
LimitCORE=infinity
# Comment TasksMax if your systemd version does not support it.
# Only systemd 226 and above support this option.
TasksMax=infinity
# set delegate yes so that systemd does not reset the cgroups of docker containers
Delegate=yes
# kill only the docker process, not all processes in the cgroup
KillMode=process
OOMScoreAdjust=-500
[Install]
WantedBy=multi-user.target
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| [root@node1 ~]# systemctl daemon-reload
[root@node1 ~]# systemctl restart docker
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| [root@node1 ~]# ip a s
......
5: docker0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default
link/ether 02:42:63:d1:9e:0b brd ff:ff:ff:ff:ff:ff
inet 172.21.31.1/24 brd 172.21.31.255 scope global docker0
valid_lft forever preferred_lft forever
6: flannel0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1472 qdisc pfifo_fast state UNKNOWN group default qlen 500
link/none
inet 172.21.31.0/16 scope global flannel0
valid_lft forever preferred_lft forever
inet6 fe80::edfa:d8b0:3351:4126/64 scope link flags 800
valid_lft forever preferred_lft forever
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| [root@node2 ~]# systemctl daemon-reload
[root@node2 ~]# systemctl restart docker
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| [root@node2 ~]# ip a s
......
5: docker0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default
link/ether 02:42:e1:16:68:de brd ff:ff:ff:ff:ff:ff
inet 172.21.55.1/24 brd 172.21.55.255 scope global docker0
valid_lft forever preferred_lft forever
6: flannel0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1472 qdisc pfifo_fast state UNKNOWN group default qlen 500
link/none
inet 172.21.55.0/16 scope global flannel0
valid_lft forever preferred_lft forever
inet6 fe80::f895:9b5a:92b1:78aa/64 scope link flags 800
valid_lft forever preferred_lft forever
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| [root@node1 ~]# docker run -it --rm busybox:latest
/ # ifconfig
eth0 Link encap:Ethernet HWaddr 02:42:AC:15:1F:02
inet addr:172.21.31.2 Bcast:172.21.31.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1472 Metric:1
RX packets:21 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:2424 (2.3 KiB) TX bytes:0 (0.0 B)
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:65536 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
/ # ping 172.21.55.2
PING 172.21.55.2 (172.21.55.2): 56 data bytes
64 bytes from 172.21.55.2: seq=0 ttl=60 time=2.141 ms
64 bytes from 172.21.55.2: seq=1 ttl=60 time=1.219 ms
64 bytes from 172.21.55.2: seq=2 ttl=60 time=0.730 ms
^C
--- 172.21.55.2 ping statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/max = 0.730/1.363/2.141 ms
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| [root@node2 ~]# docker run -it --rm busybox:latest
/ # ifconfig
eth0 Link encap:Ethernet HWaddr 02:42:AC:15:37:02
inet addr:172.21.55.2 Bcast:172.21.55.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1472 Metric:1
RX packets:19 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:2246 (2.1 KiB) TX bytes:0 (0.0 B)
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:65536 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
/ # ping 172.21.31.2
PING 172.21.31.2 (172.21.31.2): 56 data bytes
64 bytes from 172.21.31.2: seq=0 ttl=60 time=1.286 ms
64 bytes from 172.21.31.2: seq=1 ttl=60 time=0.552 ms
^C
--- 172.21.31.2 ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max = 0.552/0.919/1.286 ms
|