Running UpSnap from a bridge?

[Jaxel]

I try to keep all my Docker containers bridged, rather than on my host network. I'm having trouble configuring UpSnap for this.

This is my Docker compose:

services:
  upsnap:
    image: ghcr.io/seriousm4x/upsnap:latest
    container_name: upsnap
    restart: unless-stopped
    network_mode: bridge
    ports:
      - 8090:8090
    volumes:
      - ./data:/app/pb_data

The problem I am having is that running a network scan in UpSnap doesn't find any of my devices. If I switch the network_mode to host, it can find my devices; but as I said, I'm trying to keep all my containers bridged.

What would I need to do, to get this working?

[seriousm4x]

I just did a little digging if thats possible.
The first answer that came up was this: https://stackoverflow.com/a/67018294

But I've found a blog post which might help you: https://www.devwithimagination.com/2020/06/15/homebridge-docker-and-wake-on-lan/
It's using a bridged network with a fixed ip address. Let me know if you can get it to work.

[MirisWisdom]

Steps which worked on my end:

1. Create an external network bridge: docker network create biscuit-network
2. In Docker Compose, link the UpSnap container to the created network bridge:

services:
  upsnap:
    # ...

networks:
  default:
    name: biscuit-network
    external: true

3. On the Docker host, instruct sysctl with the following parameters:

sudo su

interface=$(docker network inspect biscuit-network --format '{{.Id}}')
interface=br-${interface:0:12}

sysctl net.ipv4.icmp_echo_ignore_broadcasts=0
sysctl net.ipv4.conf.all.bc_forwarding=1
sysctl net.ipv4.conf.${interface}.bc_forwarding=1

Tips:

You can persist the sysctl declarations, e.g. in /etc/sysctl.d/99-upsnap.conf.

To manually get the name of your bridge interface on the host, invoke docker network ls and refer to the NETWORK ID column; then, prepend the value with br-, e.g. br-0946aec19ca1.

You can also confirm it with:

ip a | grep 0946aec19ca1

# 6: br-0946aec19ca1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default 
#     link/ether 02:42:65:c0:2e:a2 brd ff:ff:ff:ff:ff:ff
#     inet 172.18.0.1/16 brd 172.18.255.255 scope global br-0946aec19ca1
#        valid_lft forever preferred_lft forever
#     inet6 fe80::42:65ff:fec0:2ea2/64 scope link proto kernel_ll 
#        valid_lft forever preferred_lft foreve