Originating traffic from container from a specific IP address

Apps and Virtualization
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1

Hi,

I’ve just upgraded from 24.04 to 24.10, and am struggling to get things back to the way they were in terms of networking with my custom apps.

Before, I had some containers bound to specific IP addresses on the local network such that outbound connections from those containers would come from a specific IP address on the TrueNAS box. However, I’m struggling to do this now that we’ve moved away from k8s.

To be clear, I can bind ports to a specific IP address such that the box will listen for connections on the correct IP address. It’s traffic originating from the containers that I need to come from specific IP addresses. At the moment it all comes from the first IP address on the TrueNAS’s interface.

I’ve tried setting com.docker.network.bridge.host_binding_ipv4 on the Docker network in the custom app YAML but it doesn’t seem to make any difference in this sense. All the other solutions I can find online involve custom iptables rules which I’d obviously like to avoid.

Is there another way of reproducing the behaviour I was able to get with 24.04?

Many thanks!

2

Use the com.docker.network.host_ipv4 option on the bridge network. It will add the correct iptables SNAT rule.

Here is the setup I used to verify that it works. Tested on TrueNAS Scale 24.10.0.2.

# Add secondary IP Adresss
$ sudo ip addr add 192.168.0.201/24 dev eno4

# Create bridge network "testnet"
$ sudo docker network create --driver=bridge --subnet=10.7.8.0/24 --gateway=10.7.8.1 --opt=com.docker.network.host_ipv4=192.168.0.201 testnet

# Verify that docker created the correct SNAT rule
$ sudo iptables-save | grep -i SNAT
-A POSTROUTING -s 10.7.8.0/24 ! -o br-3ffdb8cd1871 -j SNAT --to-source 192.168.0.201

# Launch test container
$ sudo docker run --rm --network=testnet docker.io/alpine/curl http://192.168.0.198:8000

# Test Result: Destination machine correctly sees 192.168.0.201 as the source ip
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3

Amazing, thank you! That works like a charm.

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