Give internet access to a docker container network

nat-masquerade-docker.md

If you docker container has no internet connection maybe you docker network neither have it.

1. Get virtual container bridge name:

network_name=$(docker inspect --format '{{ range $key, $value := .NetworkSettings.Networks }}{{ $key }}{{ end }}' $container)
etwork_id=$(docker network inspect -f {{.Id}} $network_name)
bridge_name="br-${network_id:0:12}"

2. Obtain IP network address of the virtual bridge:

IP=$(ip addr show $bridge_name | grep 'inet ' | awk '{print $2}')	

3. Masquerade all outgoing traffic from the $IP subnet:

sudo iptables -t nat -A POSTROUTING ! -o $bridge_name -s $IP -j MASQUERADE

4. Check it:

user@host:~$ docker exec -u 0 -it $container /bin/bash 
root@772bc683889a:/var/www/html# ping 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=118 time=12.1 ms
64 bytes from 8.8.8.8: icmp_seq=2 ttl=118 time=9.50 ms
64 bytes from 8.8.8.8: icmp_seq=3 ttl=118 time=4.98 ms
^C
--- 8.8.8.8 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2003ms
rtt min/avg/max/mdev = 4.979/8.850/12.070/2.931 m