Container is not able to connect to the internet using the bridge network on Synology DSM 7.2

I tried to install the latest redmine image (5.1.2) after using redmine up to version 4.2.1 since a few years. I found that the actual image is not able to load ruby from the server which seems to be included up to version 5.1.0 of the image. At least 5.1.0 is the last version, which runs on my Synology ds920 (system and packages most recent versions). Also email is not available. So the bridge network seems not to be able to connect to the internet.

I set up a rule in the firewall to enable all ports for the bridge network IPs (172.18.0.0/16). But to no avail.

So: Sameersbn/redmine runs well up to version 5.1.0. Starting from 5.1.1 it doesn ´t boot up as the container cannot load ruby from th servers. It seems that the bridge network is blocked by Synology dsm, so that it is not able to get to the internet. Access to the redmine website is perfectly possible via the configured ports or via reverse proxy on my ds.

I tried to several versions of the image and defined version 5.1.1 onward as the ones where the problems started. The only difference in the container settings where that before 5.1 ruby 2.5 was included whereas starting from 5.1. ruby 3.2 is downloaded from a server.

Even before push emails and notifications could not be sent by the container. (So the principal problem existed from the beginning, it just wasn ´t so visible as I didn’t need notifications then.)

i introduced a rule in the firewall which allowed all ports for the bridge-networks ip addresses. I hoped that that would grant access to the internet for the container. Nothing happened.

I switched to the host network. There redmine booted up to version 5.1.2 but I was not able to get access to the container (defined port 30001 as redmine port and outgoing port of the container.

So there seems to be something fundamentally flawed in the networking settings either on the side of the container or Synology ´s.

An help? The ping-command seems not to be available in the container´s terminal. Is that true?

The report names no repository file, test, or entry point. Start by comparing image versions 5.1.0 and 5.1.1 on Synology DSM 7.2 with the bridge network, checking whether the container can reach the server used to download Ruby; also compare host networking and the reported port mapping. Done means identifying a reproducible networking cause or documenting that it is specific to the Synology environment.