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Docker firewall question (lemmy.ml)

submitted 3 weeks ago* (last edited 3 weeks ago) by [email protected] to c/[email protected]

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I've recently learned that UFW firewall rules do not affect Docker containers. I am looking into learning firewall rules in depth but in the meantime I want make sure I don't fuck something up, so here are a few questions:

1- On a host that drops all incoming connections (configured through UFW), if I have a container with only a single port mapping 127.0.0.1:8080:80 is there any way to access this container through the public internet, what about 8080:80 or no port mapping at all?

2- How do I drop all incoming connections to all Docker containers and do I need to do that? Similar to ufw default deny incoming?

3- Is there a way to see all incoming/outgoing connections of all containers?

Thanks in advance and any resource advice for securing docker for dummies is appreciated.

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[–] [email protected] 10 points 3 weeks ago (1 children)

With Docker, the internal network is just a bridge interface. The reason most firewall rules don't apply is a combination of:

Containers have their own namespace including network namespace, so each container have a blank iptables just for them.
For container communication, that goes through the FORWARD table, not the INPUT/OUTPUT ones.
Docker adds its own rules to ensure that this works as expected.

The only thing that should be affected by the host firewall is the proxy service Docker uses to listen on a port on the host and send it to the container.

When using Docker, each container acts like an independent machine, and your host gets configured to act as a router. You can firewall Docker containers, the rules just need to be in the right place to work.

[–] [email protected] 1 points 3 weeks ago* (last edited 3 weeks ago)

Thanks, just to clarify, even if I deny all forwards on the host using UFW, that still won't have an affect on Docker because Docker inserts its rules above UFW rules. Correct?