In environments without internet access and without a DNS resolver (fully offline setups), the use of socket.gethostbyname("host.docker.internal") causes a 15-second delay on every request due to DNS resolution timeout. This is particularly problematic when DEBUG = True is required during development or internal deployments.

Details:
I encountered this issue in a system that must remain completely offline (air-gapped). There is no DNS resolver available, and thus, any DNS lookup (such as for host.docker.internal) results in a timeout of ~15 seconds. The following code snippet demonstrates the issue:

    if not settings.DEBUG:
        return False

    # Test: settings
    if request.META.get("REMOTE_ADDR") in settings.INTERNAL_IPS:
        return True

    # Test: Docker
    try:
        # This is a hack for docker installations. It attempts to look
        # up the IP address of the docker host.
        # This is not guaranteed to work.
        docker_ip = (
            # Convert the last segment of the IP address to be .1
            ".".join(socket.gethostbyname("host.docker.internal").rsplit(".")[:-1])
            + ".1"
        )

This logic gives no way to avoid the DNS lookup if DEBUG = True. The delay occurs on every request, making development/debugging extremely painful in such setups.

Additionally, tools like the Django Debug Toolbar exacerbate the issue by triggering this DNS lookup repeatedly, which compounds the delay.

Suggested Solution:
Introduce a configurable way to bypass the host.docker.internal resolution in known offline environments. Perhaps a try-except with a timeout or a setting that disables Docker IP detection entirely.

Environment:

Offline setup (no DNS resolver, no internet)

Docker-based deployment

Django (with Debug Toolbar in development)