Docker and Iptables
Using iptables on docker host.
Issue : Docker Iptables Punch Through
Lets take following example:
A docker email container with port 25 and 587 (`-p 25:25 -p 587:587)
A docker web server container with port 80 and 443 (`-p 80:80 -p 443:443)
Iptables rules setup to block traffic from 10.10.10.0/24 to port 25, 587, 80, 443:
-A -s 10.10.10.0/24 -p tcp -m multiport --dports 25,587 -j DROP -A -s 10.10.10.0/24 -p tcp -m multiport --dports 80,443 -j DROP
But 10.10.10.0/24 traffic will bypass the above two rules and reach the email and web containers. That is because docker is using its own chain for routing traffic for its containers.
Fix : Custom Chain and DOCKER-USER
Docker does provide a specific chain,
DOCKER-USER, for us to setup custom rules that need to be applied to container traffic.
To reduce effort applying rules to both default INPUT chain and DOCKER-USER chain, we will create our own chain and append it to them.
As shown above, we will always add our rules to
my_chain, and it will be automatically applied to both