DNS resolution failing

[cabadam]

I have a brand new installation of netbox running through Docker. It appears that hostnames will not resolve within the container. The default dashboard widget for "NetBox News" displays an error:

There was a problem fetching the RSS feed: HTTPSConnectionPool(host='api.netbox.oss.netboxlabs.com', port=443): Max retries exceeded with url: /v1/newsfeed/ (Caused by NameResolutionError("<urllib3.connection.HTTPSConnection object at 0xffffa9d12750>: Failed to resolve 'api.netbox.oss.netboxlabs.com' ([Errno -3] Temporary failure in name resolution)"))

I was trying to configure OIDC authentication and when selected it logs:

<class 'social_core.exceptions.AuthConnectionError'>

Connection error: HTTPSConnectionPool(host='my.oidc.hostname', port=443): Max retries exceeded with url: /oidc-path/.well-known/openid-configuration (Caused by NameResolutionError("<urllib3.connection.HTTPSConnection object at 0xffffa8c00d40>: Failed to resolve 'my.oidc.hostname' ([Errno -3] Temporary failure in name resolution)"))

Python version: 3.12.3
NetBox version: 4.4.5-Docker-3.4.1
Plugins: None installed

I launched a /bin/bash shell into the netbox container to try to troubleshoot, saw that dig was not available. I wanted to try to install it, and when I ran "apt-get update", that command failed with:

W: Failed to fetch http://ports.ubuntu.com/ubuntu-ports/dists/noble/InRelease Temporary failure resolving 'ports.ubuntu.com'
W: Failed to fetch http://ports.ubuntu.com/ubuntu-ports/dists/noble-updates/InRelease Temporary failure resolving 'ports.ubuntu.com'
W: Failed to fetch http://ports.ubuntu.com/ubuntu-ports/dists/noble-backports/InRelease Temporary failure resolving 'ports.ubuntu.com'
W: Failed to fetch http://ports.ubuntu.com/ubuntu-ports/dists/noble-security/InRelease Temporary failure resolving 'ports.ubuntu.com'
W: Failed to fetch http://packages.nginx.org/unit/ubuntu/dists/noble/InRelease Temporary failure resolving 'packages.nginx.org'
W: Some index files failed to download. They have been ignored, or old ones used instead.

Looking up these hostnames from the Docker host as well as from other containers running on the same host works fine. I tried rebooting the entire host, no change.

Is there something odd about DNS in this application/environment?

[cabadam]

Well, answering my own question. I forgot this Docker environment (not netbox specific) DOES have a DNS quirk that requires me to manually specify the DNS server for containers.

For Netbox, I fixed this by modifying docker-compose.override.yml to add:

services:
  netbox:
    dns:
      - 192.168.86.28