Problem

I am running a docker container (snapcast server) and need to run it in host mode.

Before I ran it in host mode I forwarded ports 1704, 1705 and 1780 (where the Web UI is reachable on port 1780) in my docker-compose.yml and everything worked when doing it like that.
When I changed my docker-compose to use network_mode: host the container started as expected and logs looked normal.

However the Web UI is not reachable (and connections via the other ports cannot be made).

What I did / what my understanding is

As far as I understood a docker container in network_mode:host is running directly on the host container and thus uses the ports of the host directly wihtout any port mappings so I expected to be able to reach the container just like I did when it ran normally (as I mapped port 1705:1705 and so on).

I tried to look at the open ports using netstat -tunlp, when I do that I see that a TCP listening on all three ports is active which is why I really do not understand why this does not work.

Netstat output:

tcp        0      0 0.0.0.0:1780            0.0.0.0:*               LISTEN      4132631/snapserver   
tcp        0      0 0.0.0.0:1704            0.0.0.0:*               LISTEN      4132631/snapserver  
tcp        0      0 0.0.0.0:1705            0.0.0.0:*               LISTEN      4132631/snapserver

So I have a container that seems to start normally and a “confirmation” that there is active listening on the ports I need yet I cannot make a connection.

Furthermore I have trid to do the same with another container. When I changed the compose file to use network_mode: host and restarted the container it was reachable just like it was before so I do not think that it is a docker config problem.

Resources needed for reproduction

Dockerfile

FROM alpine:edge AS builder
WORKDIR /snapcast

RUN apk add npm curl alpine-sdk
RUN npm install --silent --save-dev -g [email protected]
RUN wget https://github.com/badaix/snapweb/archive/refs/tags/v0.7.0.tar.gz 
RUN tar xzf v0.7.0.tar.gz --directory /
WORKDIR /snapweb-0.7.0
RUN npm ci
RUN npm run build


FROM alpine:edge

RUN echo "https://dl-cdn.alpinelinux.org/alpine/edge/testing/" >> /etc/apk/repositories
RUN echo "https://dl-cdn.alpinelinux.org/alpine/edge/community/" >> /etc/apk/repositories
RUN apk add --no-cache gdb librespot snapcast dbus avahi avahi-compat-libdns_sd

COPY --from=builder /snapweb-0.7.0/dist /usr/share/snapserver/snapweb
COPY snapserver.conf /etc/snapserver.conf
COPY startup.sh startup.sh
RUN chmod +x ./startup.sh

EXPOSE 1704 1705 1780
ENTRYPOINT [ "./startup.sh" ]

startup.sh used by Dockerfile

#!/usr/bin/env sh

dbus-daemon --system
avahi-daemon --no-chroot &
/usr/bin/snapserver $EXTRA_ARGS

snapserver.conf used by Dockerfile

[stream]
source = tcp://0.0.0.0?name=Snapserver

[http]
doc_root = /usr/share/snapserver/snapweb

docker-compose.yml

version: '3'
services:
  snapserver:
    image: tiko/snapcastserver:latest
    container_name: snapserver
    restart: unless-stopped
    network_mode: host
    volumes:
      - /root/snapcastserver/snapserver.conf:/etc/snapserver.conf

Reproduction steps

1. Build the image using my Dockerfile (remembre to tag accordingly and change dockerfile to use correct image)
2. Start the container using my docker-compose.yml
3. The WebUI should be reachable on your-ip:1780 but it isn’t for me

Any help is appreciated, thank you!