Detailed explanation of direct routing in cross-host communication of Docker containers

The IP address of host 1 is: 192.168.145.128
The IP address of host 2 is: 192.168.145.129
Subnet assigned to Docker container on Host 1: 172.17.1.0/24
Subnet assigned to Docker containers on Host 2: 172.17.2.0/24
After this configuration, the Docker containers on the two hosts will definitely not use the same IP address, thus avoiding IP conflicts.

To summarize, the data packet transmission process between two containers is as follows:
The data packet sent from container1 to container2 is first sent to the "gateway" docker0 of container1, and then by looking up the route of host1, it is found that the data packet needs to be sent to host2. After the data packet arrives at host2, it is forwarded to docker0 of host2, and finally it is transferred to container2 by docker0. The reverse principle is the same and will not be repeated here.

Edit the /etc/docker/daemon.json file on host 1 and add the following content: "bip" : "ip/netmask"
{ "bip", "172.17.1.252/24" }

Edit the /etc/docker/daemon.json file on host 2 and add the following content: "bip" : "ip/netmask"
{ "bip", "172.17.2.252/24" }

Restart the docker service. Execute the following command on both host 1 and host 2 to restart the docker service so that the modified docker0 network segment will take effect. systemctl restart docker

Add routing rules on host 1 as follows:
route add -net 172.17.2.0 netmask 255.255.255.0 gw 192.168.145.129

Add routing rules on host 2 as follows:
route add -net 172.17.1.0 netmask 255.255.255.0 gw 192.168.145.128

Add the following rules on host 1:
iptables -t nat -F POSTROUTING
iptables -t nat -A POSTROUTING -s 172.17.1.0/24 ! -d 172.17.0.0/16 -j MASQUERADE

Add the following rules on host 2:
iptables -t nat -F POSTROUTING
iptables -t nat -A POSTROUTING -s 172.17.2.0/24 ! -d 172.17.0.0/16 -j MASQUERADE

Start the centos container on host 1:
docker run -it --name container1 centos /bin/bash

Start the centos container on host 2:
docker run -it --name container2 centos /bin/bash

root@rancher:~# vi /etc/rc.local

Add routing information, remember to write it before exit! ! ! :
route add -net 172.17.2.0 netmask 255.255.255.0 gw 192.168.102.88