不可错过!5 张图带你搞懂容器网络原理
文章转载:高效运维 原文链接:https://iximiuz.com/en/posts/container-networking-is-simple/
如何虚拟化网络资源,让容器认为自己拥有独占网络? 如何让容器们和平共处,之间不会互相干扰,并且能够互相通信? 从容器内部如何访问外部世界(比如,互联网)? 从外部世界如何访问某台机器上的容器呢(比如,端口发布)?
网络命名空间(namespace) 虚拟 Ethernet设备(veth) 虚拟网络交换机(网桥) IP路由和网络地址翻译(NAT) 并且不需要任何代码就可以让这样的网络魔法发生……
前提条件
$ vagrant init centos/8
$ vagrant up
$ vagrant ssh
[vagrant@localhost ~]$ uname -a
Linux localhost.localdomain 4.18.0-147.3.1.el8_1.x86_64
network 命名空间隔离容器
inspect-net-stack.sh
:#!/usr/bin/env bash
echo "> Network devices"
ip link
echo -e "\n> Route table"
ip route
echo -e "\n> Iptables rules"
iptables --list-rules
$ sudo iptables -N ROOT_NS
$ sudo ./inspect-net-stack.sh
> Network devices
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000 link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000 link/ether 52:54:00:e3:27:77 brd ff:ff:ff:ff:ff:ff
> Route table
default via 10.0.2.2 dev eth0 proto dhcp metric 100
10.0.2.0/24 dev eth0 proto kernel scope link src 10.0.2.15 metric 100
> Iptables rules
-P INPUT ACCEPT
-P FORWARD ACCEPT
-P OUTPUT ACCEPT
-N ROOT_NS
$ sudo ip netns add netns0
$ ip netns
netns0
如何使用刚才创建的命名空间呢?一个很好用的命令 nsenter。进入一个或多个特定的命名空间,然后执行指定的脚本:
$ sudo nsenter --net=/var/run/netns/netns0 bash
# 新建的 bash 进程在 netns0 里
$ sudo ./inspect-net-stack.sh
> Network devices 1: lo: <LOOPBACK> mtu 65536 qdisc noop state DOWN mode DEFAULT group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
> Route table
> Iptables rules
-P INPUT ACCEPT
-P FORWARD ACCEPT
-P OUTPUT ACCEPT
使用虚拟的 Ethernet 设备(veth)将容器连接到主机上
$ sudo ip link add veth0 type veth peer name ceth0
$ ip link
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
link/ether 52:54:00:e3:27:77 brd ff:ff:ff:ff:ff:ff
5: ceth0@veth0: <BROADCAST,MULTICAST,M-DOWN> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
link/ether 66:2d:24:e3:49:3f brd ff:ff:ff:ff:ff:ff
6: veth0@ceth0: <BROADCAST,MULTICAST,M-DOWN> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
link/ether 96:e8:de:1d:22:e0 brd ff:ff:ff:ff:ff:ff
$ sudo ip link set ceth0 netns netns0
# 列出所有设备,可以看到 ceth0 已经从 root 栈里消失了
$ ip link 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
link/ether 52:54:00:e3:27:77 brd ff:ff:ff:ff:ff:ff
6: veth0@if5: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
link/ether 96:e8:de:1d:22:e0 brd ff:ff:ff:ff:ff:ff link-netns netns0
$ sudo ip link set veth0 up
$ sudo ip addr add 172.18.0.11/16 dev veth0
$ sudo nsenter --net=/var/run/netns/netns0
$ ip link set lo up
$ ip link set ceth0 up
$ ip addr add 172.18.0.10/16 dev ceth0
$ ip link
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
5: ceth0@if6: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default qlen 1000
link/ether 66:2d:24:e3:49:3f brd ff:ff:ff:ff:ff:ff link-netnsid 0
# 在 netns0 里 ping root 的 veth0
$ ping -c 2 172.18.0.11
PING 172.18.0.11 (172.18.0.11) 56(84) bytes of data.
64 bytes from 172.18.0.11: icmp_seq=1 ttl=64 time=0.038 ms
64 bytes from 172.18.0.11: icmp_seq=2 ttl=64 time=0.040 ms
--- 172.18.0.11 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 58ms
rtt min/avg/max/mdev = 0.038/0.039/0.040/0.001 ms
# 离开 netns0
$ exit
# 在root命名空间里ping ceth0
$ ping -c 2 172.18.0.10
PING 172.18.0.10 (172.18.0.10) 56(84) bytes of data.
64 bytes from 172.18.0.10: icmp_seq=1 ttl=64 time=0.073 ms
64 bytes from 172.18.0.10: icmp_seq=2 ttl=64 time=0.046 ms
--- 172.18.0.10 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 3ms
rtt min/avg/max/mdev = 0.046/0.059/0.073/0.015 ms
# 在 root 命名空间
$ ip addr show dev eth0
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
link/ether 52:54:00:e3:27:77 brd ff:ff:ff:ff:ff:ff
inet 10.0.2.15/24 brd 10.0.2.255 scope global dynamic noprefixroute eth0
valid_lft 84057sec preferred_lft 84057sec
inet6 fe80::5054:ff:fee3:2777/64 scope link
valid_lft forever preferred_lft forever
# 记住这里 IP 是 10.0.2.15
$ sudo nsenter --net=/var/run/netns/netns0
# 尝试ping主机的eth0
$ ping 10.0.2.15
connect: Network is unreachable
# 尝试连接外网
$ ping 8.8.8.8
connect: Network is unreachable
# 在netns0命名空间:
$ ip route
172.18.0.0/16 dev ceth0 proto kernel scope link src 172.18.0.10
# 在root命名空间:
$ ip route
# ... 忽略无关行 ...
172.18.0.0/16 dev veth0 proto kernel scope link src 172.18.0.11
使用虚拟网络 switch(网桥)连接容器
# 从 root 命名空间
$ sudo ip netns add netns1
$ sudo ip link add veth1 type veth peer name ceth1
$ sudo ip link set ceth1 netns netns1
$ sudo ip link set veth1 up
$ sudo ip addr add 172.18.0.21/16 dev veth1
$ sudo nsenter --net=/var/run/netns/netns1
$ ip link set lo up
$ ip link set ceth1 up
$ ip addr add 172.18.0.20/16 dev ceth1
$ ip route
# ... 忽略无关行... #
172.18.0.0/16 dev veth0 proto kernel scope link src 172.18.0.11
172.18.0.0/16 dev veth1 proto kernel scope link src 172.18.0.21
在添加了第二个 veth 对之后,root 的网络栈知道了新路由 172.18.0.0/16 dev veth1 proto kernel scope link src 172.18.0.21,但是之前已经存在该网络的路由了。当第二个容器尝试 ping veth1 时,选中的是第一个路由规则,这导致网络无法连通。如果我们删除第一个路由 sudo ip route delete 172.18.0.0/16 dev veth0 proto kernel scope link src 172.18.0.11,然后重新检查连通性,应该就没有问题了。netns1 可以连通,但是 netns0 就不行了。
$ sudo ip netns delete netns0
$ sudo ip netns delete netns1
$ sudo ip link delete veth0
$ sudo ip link delete ceth0
$ sudo ip link delete veth1
$ sudo ip link delete ceth1
$ sudo ip netns add netns0
$ sudo ip link add veth0 type veth peer name ceth0
$ sudo ip link set veth0 up
$ sudo ip link set ceth0 netns netns0
$ sudo nsenter --net=/var/run/netns/netns0
$ ip link set lo up
$ ip link set ceth0 up
$ ip addr add 172.18.0.10/16 dev ceth0
$ exit
$ sudo ip netns add netns1
$ sudo ip link add veth1 type veth peer name ceth1
$ sudo ip link set veth1 up
$ sudo ip link set ceth1 netns netns1
$ sudo nsenter --net=/var/run/netns/netns1
$ ip link set lo up
$ ip link set ceth1 up
$ ip addr add 172.18.0.20/16 dev ceth1
$ exit
$ ip route
default via 10.0.2.2 dev eth0 proto dhcp metric 100
10.0.2.0/24 dev eth0 proto kernel scope link src 10.0.2.15 metric 100
$ sudo ip link add br0 type bridge
$ sudo ip link set br0 up
$ sudo ip link set veth0 master br0
$ sudo ip link set veth1 master br0
$ sudo nsenter --net=/var/run/netns/netns0
$ ping -c 2 172.18.0.20
PING 172.18.0.20 (172.18.0.20) 56(84) bytes of data.
64 bytes from 172.18.0.20: icmp_seq=1 ttl=64 time=0.259 ms
64 bytes from 172.18.0.20: icmp_seq=2 ttl=64 time=0.051 ms
--- 172.18.0.20 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 2ms
rtt min/avg/max/mdev = 0.051/0.155/0.259/0.104 ms
$ sudo nsenter --net=/var/run/netns/netns1
$ ping -c 2 172.18.0.10
PING 172.18.0.10 (172.18.0.10) 56(84) bytes of data.
64 bytes from 172.18.0.10: icmp_seq=1 ttl=64 time=0.037 ms
64 bytes from 172.18.0.10: icmp_seq=2 ttl=64 time=0.089 ms
--- 172.18.0.10 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 36ms
rtt min/avg/max/mdev = 0.037/0.063/0.089/0.026 ms
$ sudo nsenter --net=/var/run/netns/netns0
$ ip neigh
172.18.0.20 dev ceth0 lladdr 6e:9c:ae:02:60:de STALE
$ exit
$ sudo nsenter --net=/var/run/netns/netns1
$ ip neigh
172.18.0.10 dev ceth1 lladdr 66:f3:8c:75:09:29 STALE
$ exit
连接外部世界( IP 路由和地址伪装(masquerading))
$ sudo nsenter --net=/var/run/netns/netns0
$ ping 10.0.2.15 # eth0 address
connect: Network is unreachable
这里很明显,netns0 没有路由:
$ ip route
172.18.0.0/16 dev ceth0 proto kernel scope link src 172.18.0.10
# 首先使用 exit 离开netns0:
$ ping -c 2 172.18.0.10
PING 172.18.0.10 (172.18.0.10) 56(84) bytes of data.
From 213.51.1.123 icmp_seq=1 Destination Net Unreachable
From 213.51.1.123 icmp_seq=2 Destination Net Unreachable
--- 172.18.0.10 ping statistics ---
2 packets transmitted, 0 received, +2 errors, 100% packet loss, time 3ms
$ ping -c 2 172.18.0.20
PING 172.18.0.20 (172.18.0.20) 56(84) bytes of data.
From 213.51.1.123 icmp_seq=1 Destination Net Unreachable
From 213.51.1.123 icmp_seq=2 Destination Net Unreachable
--- 172.18.0.20 ping statistics ---
2 packets transmitted, 0 received, +2 errors, 100% packet loss, time 3ms
$ sudo ip addr add 172.18.0.1/16 dev br0
$ ip route
# ...忽略无关行 ...
172.18.0.0/16 dev br0 proto kernel scope link src 172.18.0.1
$ ping -c 2 172.18.0.10
PING 172.18.0.10 (172.18.0.10) 56(84) bytes of data.
64 bytes from 172.18.0.10: icmp_seq=1 ttl=64 time=0.036 ms
64 bytes from 172.18.0.10: icmp_seq=2 ttl=64 time=0.049 ms
--- 172.18.0.10 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 11ms
rtt min/avg/max/mdev = 0.036/0.042/0.049/0.009 ms
$ ping -c 2 172.18.0.20
PING 172.18.0.20 (172.18.0.20) 56(84) bytes of data.
64 bytes from 172.18.0.20: icmp_seq=1 ttl=64 time=0.059 ms
64 bytes from 172.18.0.20: icmp_seq=2 ttl=64 time=0.056 ms
--- 172.18.0.20 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 4ms
rtt min/avg/max/mdev = 0.056/0.057/0.059/0.007 ms
$ sudo nsenter --net=/var/run/netns/netns0
$ ip route add default via 172.18.0.1
$ ping -c 2 10.0.2.15
PING 10.0.2.15 (10.0.2.15) 56(84) bytes of data.
64 bytes from 10.0.2.15: icmp_seq=1 ttl=64 time=0.036 ms
64 bytes from 10.0.2.15: icmp_seq=2 ttl=64 time=0.053 ms
--- 10.0.2.15 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 14ms
rtt min/avg/max/mdev = 0.036/0.044/0.053/0.010 ms
# 为`netns1`也做上述配置
# 在 root 命名空间
sudo bash -c 'echo 1 > /proc/sys/net/ipv4/ip_forward'
$ sudo nsenter --net=/var/run/netns/netns0
$ ping 8.8.8.8
# hung住了...
$ sudo iptables -t nat -A POSTROUTING -s 172.18.0.0/16 ! -o br0 -j MASQUERADE
$ sudo nsenter --net=/var/run/netns/netns0
$ ping -c 2 8.8.8.8 PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.
64 bytes from 8.8.8.8: icmp_seq=1 ttl=61 time=43.2 ms
64 bytes from 8.8.8.8: icmp_seq=2 ttl=61 time=36.8 ms
--- 8.8.8.8 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 2ms
rtt min/avg/max/mdev = 36.815/40.008/43.202/3.199 ms
sudo iptables -S
-P INPUT ACCEPT
-P FORWARD ACCEPT
-P OUTPUT ACCEPT
Docker 默认限制所有流量,随后仅仅为已知的路径启用路由。
如下是在 CentOS 8 机器上,单个容器暴露了端口 5005 时,由 Docker daemon 生成的规则:
$ sudo iptables -t filter --list-rules
-P INPUT ACCEPT
-P FORWARD DROP
-P OUTPUT ACCEPT
-N DOCKER
-N DOCKER-ISOLATION-STAGE-1
-N DOCKER-ISOLATION-STAGE-2
-N DOCKER-USER
-A FORWARD -j DOCKER-USER
-A FORWARD -j DOCKER-ISOLATION-STAGE-1
-A FORWARD -o docker0 -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
-A FORWARD -o docker0 -j DOCKER
-A FORWARD -i docker0 ! -o docker0 -j ACCEPT
-A FORWARD -i docker0 -o docker0 -j ACCEPT
-A DOCKER -d 172.17.0.2/32 ! -i docker0 -o docker0 -p tcp -m tcp --dport 5000 -j ACCEPT
-A DOCKER-ISOLATION-STAGE-1 -i docker0 ! -o docker0 -j DOCKER-ISOLATION-STAGE-2
-A DOCKER-ISOLATION-STAGE-1 -j RETURN
-A DOCKER-ISOLATION-STAGE-2 -o docker0 -j DROP
-A DOCKER-ISOLATION-STAGE-2 -j RETURN
-A DOCKER-USER -j RETURN
$ sudo iptables -t nat --list-rules
-P PREROUTING ACCEPT
-P INPUT ACCEPT
-P POSTROUTING ACCEPT
-P OUTPUT ACCEPT
-N DOCKER
-A PREROUTING -m addrtype --dst-type LOCAL -j DOCKER
-A POSTROUTING -s 172.17.0.0/16 ! -o docker0 -j MASQUERADE
-A POSTROUTING -s 172.17.0.2/32 -d 172.17.0.2/32 -p tcp -m tcp --dport 5000 -j MASQUERADE
-A OUTPUT ! -d 127.0.0.0/8 -m addrtype --dst-type LOCAL -j DOCKER
-A DOCKER -i docker0 -j RETURN
-A DOCKER ! -i docker0 -p tcp -m tcp --dport 5005 -j DNAT --to-destination 172.17.0.2:5000
$ sudo iptables -t mangle --list-rules
-P PREROUTING ACCEPT
-P INPUT ACCEPT
-P FORWARD ACCEPT
-P OUTPUT ACCEPT
-P POSTROUTING ACCEPT
$ sudo iptables -t raw --list-rules
-P PREROUTING ACCEPT
-P OUTPUT ACCEPT
让外部世界可以访问容器(端口发布)
$ sudo nsenter --net=/var/run/netns/netns0
$ python3 -m http.server --bind 172.18.0.10 5000
# 从 root 命名空间
$ curl 172.18.0.10:5000
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
# ... 忽略无关行 ...
$ curl 10.0.2.15:5000
curl: (7) Failed to connect to 10.0.2.15 port 5000: Connection refused
# 外部流量
sudo iptables -t nat -A PREROUTING -d 10.0.2.15 -p tcp -m tcp --dport 5000 -j DNAT --to-destination 172.18.0.10:5000
# 本地流量 (因为它没有通过 PREROUTING chain)
sudo iptables -t nat -A OUTPUT -d 10.0.2.15 -p tcp -m tcp --dport 5000 -j DNAT --to-destination 172.18.0.10:5000
sudo modprobe br_netfilter
curl 10.0.2.15:5000
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
# ... 忽略无关行 ...
理解 Docker 网络驱动
--network host
模式开始。试着比较一下命令 ip link
和 sudo docker run -it --rm --network host alpine ip link
的输出。它们几乎一样!在 host 模式下,Docker 简单地没有使用网络命名空间隔离,容器就在 root 网络命名空间里工作,并且和主机共享网络栈。rootless 容器和网络
结论
END
官方站点:www.linuxprobe.com
Linux命令大全:www.linuxcool.com
刘遄老师QQ:5604241
Linux技术交流群:3762708
(新群,火热加群中……)
想要学习Linux系统的读者可以点击"阅读原文"按钮来了解书籍《Linux就该这么学》,同时也非常适合专业的运维人员阅读,成为辅助您工作的高价值工具书!
微信扫码关注该文公众号作者
戳这里提交新闻线索和高质量文章给我们。
来源: qq
点击查看作者最近其他文章