无法访问你试图使用的功能所在的网络位置。是什么原因?
1091
2022-05-30
使用容器总是感觉像使用魔法一样。对于那些理解底层原理的人来说容器很好用,但是对于不理解的人来说就是个噩梦。很幸运的是,我们已经研究容器技术很久了,甚至成功揭秘容器只是隔离并受限的Linux进程,运行容器并不需要镜像,以及另一个方面,构建镜像需要运行一些容器。
现在是时候解决容器网络问题了。或者更准确地说,单主机容器网络问题。本文会回答这些问题:
如何虚拟化网络资源,让容器认为自己拥有独占网络?
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)
$ 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
#!/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:
2: eth0:
> 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
$ 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:
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
$ sudo ip link add veth0 type veth peer name ceth0
$ ip link
1: lo:
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: eth0:
link/ether 52:54:00:e3:27:77 brd ff:ff:ff:ff:ff:ff
5: ceth0@veth0:
link/ether 66:2d:24:e3:49:3f brd ff:ff:ff:ff:ff:ff
6: veth0@ceth0:
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:
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: eth0:
link/ether 52:54:00:e3:27:77 brd ff:ff:ff:ff:ff:ff
6: veth0@if5:
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:
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
5: ceth0@if6:
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:
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
# 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
# 从netns1无法连通root 命名空间!
$ ping -c 2 172.18.0.21
PING 172.18.0.21 (172.18.0.21) 56(84) bytes of data.
From 172.18.0.20 icmp_seq=1 Destination Host Unreachable
From 172.18.0.20 icmp_seq=2 Destination Host Unreachable
--- 172.18.0.21 ping statistics ---
2 packets transmitted, 0 received, +2 errors, 100% packet loss, time 55ms pipe 2
# 但是路由是存在的!
$ ip route
172.18.0.0/16 dev ceth1 proto kernel scope link src 172.18.0.20
# 离开 `netns1`
$ exit
# 从 root 命名空间无法连通`netns1`
$ ping -c 2 172.18.0.20
PING 172.18.0.20 (172.18.0.20) 56(84) bytes of data.
From 172.18.0.11 icmp_seq=1 Destination Host Unreachable
From 172.18.0.11 icmp_seq=2 Destination Host Unreachable
--- 172.18.0.20 ping statistics ---
2 packets transmitted, 0 received, +2 errors, 100% packet loss, time 23ms pipe 2
# 从netns0可以连通`veth1`
$ sudo nsenter --net=/var/run/netns/netns0
$ ping -c 2 172.18.0.21
PING 172.18.0.21 (172.18.0.21) 56(84) bytes of data.
64 bytes from 172.18.0.21: icmp_seq=1 ttl=64 time=0.037 ms
64 bytes from 172.18.0.21: icmp_seq=2 ttl=64 time=0.046 ms
--- 172.18.0.21 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 33ms
rtt min/avg/max/mdev = 0.037/0.041/0.046/0.007 ms
# 但是仍然无法连通netns1
$ ping -c 2 172.18.0.20
PING 172.18.0.20 (172.18.0.20) 56(84) bytes of data.
From 172.18.0.10 icmp_seq=1 Destination Host Unreachable
From 172.18.0.10 icmp_seq=2 Destination Host Unreachable
--- 172.18.0.20 ping statistics ---
2 packets transmitted, 0 received, +2 errors, 100% packet loss, time 63ms pipe 2
$ 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
$ 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
$ sudo nsenter --net=/var/run/netns/netns0
$ ping 10.0.2.15 # eth0 address
connect: Network is unreachable
$ ip route
172.18.0.0/16 dev ceth0 proto kernel scope link src 172.18.0.10
$ 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 iptables -S
-P INPUT ACCEPT
-P FORWARD ACCEPT
-P OUTPUT ACCEPT
$ 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
$ 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
# ... 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
# ... 忽略无关行 ...
slirp4netns可以用完全非特权的方式将网络命名空间连接到Internet上,通过网络命名空间里的一个TAP设备连接到用户态的TCP/IP栈(slirp)。
https://docs.docker.com/network/#network-drivers
https://www.redhat.com/sysadmin/container-networking-podman
https://github.com/rootless-containers/slirp4netns
https://developers.redhat.com/blog/2018/10/22/introduction-to-linux-interfaces-for-virtual-networking/
容器 网络 虚拟化
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