Only try resolving the docker gateway IP once per server startup and add some diagnostics

[matthiask]

Description

Please include a summary of the change and which issue is fixed. Please also
include relevant motivation and context. Your commit message should include
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Fixes #2113.

Checklist:

• I have added the relevant tests for this change.
• I have added an item to the Pending section of docs/changes.rst.

[dr-rompecabezas]

Made a general comment. Hope it helps!

[dr-rompecabezas]

This is working fine for me but I am not confident I have correctly reproduced a proper testing environment. These are the steps I took to test and my findings.

I bootstrapped a Django app using Django Cookiecutter with the Docker option, then installed the debug toolbar from your repo by replacing the pinned version with the following (and modifying the Dockerfile to install git):

git+https://github.com/matthiask/django-debug-toolbar.git@2113-dns-resolving

Then, I successfully built and ran the containers, cut off access to the Internet, and commented out the INTERNAL_IPS setting.

$ docker compose -f docker-compose.local.yml run --rm django python manage.py shell
[+] Creating 3/3
 ✔ Container djdt_docker_local_mailpit   Running                                                                                                                            0.0s 
 ✔ Container djdt_docker_local_redis     Running                                                                                                                            0.0s 
 ✔ Container djdt_docker_local_postgres  Running                                                                                                                            0.0s 
wait-for-it: waiting 30 seconds for postgres:5432
wait-for-it: postgres:5432 is available after 0 seconds
PostgreSQL is available
Python 3.12.9 (main, Mar 18 2025, 01:37:06) [GCC 12.2.0]
Type 'copyright', 'credits' or 'license' for more information
IPython 9.0.2 -- An enhanced Interactive Python. Type '?' for help.
Tip: Use `%timeit` or `%%timeit`, and the  `-r`, `-n`, and `-o` options to easily profile your code.

In [1]: from django.conf import settings

In [2]: settings.INTERNAL_IPS
Out[2]: []

Then, I confirmed the toolbar is showing and I see the following variables in the WSGI environ section of the Headers panel.

REMOTE_ADDR 	192.168.65.1
REMOTE_HOST 	192.168.65.1

I did not see any of the debug statements from this file printed in docker logs.

Honestly, I don't know what else to do to test. Perhaps you can give me some ideas tomorrow when we meet.

[matthiask]

Thank you @dr-rompecabezas

We discussed this in the Djangonauts call and come to the conclusion that we're following a different implementation strategy to fix this. I'm closing the PR.