Missing documentation of Google DNS fallback 8.8.8.8 and 8.8.4.4

[MyNameIsLame]

Is this a docs issue?

• [x] 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.