Missing documentation of Google DNS fallback 8.8.8.8 and 8.8.4.4

Is this a docs issue?

• My issue is about the documentation content or website

Type of issue

I can't find what I'm looking for

Description

Summary

Add a note to the documentation indicating that Docker falls back to Google DNS if no non-localhost DNS is defined.

Details

In one of my projects, I started a Docker container on a device without internet access and with no configured DNS other than localhost.
Inside the container, some DNS requests timed out after a long delay. I expected the DNS requests to fail immediately.

Upon checking the dockerd log, I found the following line during startup:

No non-localhost DNS nameservers are left in resolv.conf. Using default external servers: [nameserver 8.8.8.8 nameserver 8.8.4.4]

I reviewed the DNS section of the networking chapter, but found no mention of this behavior. I only discovered it referenced in another issue: https://github.com/moby/moby/issues/23910

Am I missing something?

Edit: Tested with Docker version 24.0.5, build ced0996

Location

https://docs.docker.com/engine/network/#dns-services

Suggestion

Maybe add a simple sentence to the chapter:

In case no non-localhost DNS is defined in the `/etc/resolve.conf`, a fallback to `8.8.8.8` and `8.8.4.4` will be added.

Exact formulation and placement is of course open for discussion.

Start with the DNS services section of the networking chapter at the linked documentation location and review its existing DNS behavior coverage. Add a note explaining the fallback to 8.8.8.8 and 8.8.4.4 when no non-localhost DNS is configured, then verify the rendered documentation and wording.