This is more of a bug report, at least I think it is a bug. But then I'm not sure if it's a LibreELEC bug or a bug with the Docker addon.
I'm trying to set up Miniflux in Docker on LibreELEC, I've used the Portainer addon to set up the stack and have been following Installation Instructions - Documentation
The result here should be two containers (postgres & miniflux), both placed in their own isolated bridge network by Docker (with IPs somewhere in 172.16.0.0/12). The miniflux container should be able to connect to the postgres container on port 5432 within that isolated network.
What I've found is that the Home-v4 firewall settings (haven't tested Public) prevent this.
When I disable LibreELEC's firewall in the LibreELEC settings addon and restart Docker, the miniflux container starts successfully and can communcate with the postgres container on its network. Looking at iptables -L -v confirms this, with packets showing up in the correct interface in the forward chain and hitting the isolation stages.
Though, when the Home firewall rules are enabled, packets between the two containers get rejected with connection refused somewhere and don't show up in docker's chains.
I don't know enough about iptables to get to the core of the issue, so I'm hoping someone can help with this.