How to properly setup custom handler404 in django?

As we discussed, your setup is correct, but in settings.py you should make DEBUG=False. It's more of a production feature and won't work in development environment(unless you have DEBUG=False in dev machine of course).

Debug should be False and add to view *args and **kwargs. Add to urls.py handler404 = 'view_404'

def view_404(request, *args, **kwargs):
return redirect('https://your-site/404')

If I didn't add args and kwargs server get 500.

All the other answers were not up to date. Here's what worked for me in Django 3.1:

urls.py

from django.conf.urls import handler404, handler500, handler403, handler400
from your_app_name import views

handler404 = views.error_404
handler500 = views.error_500

views.py

def error_404(request, exception):
   context = {}
   return render(request,'admin/404.html', context)

def error_500(request):
   context = {}
   return render(request,'admin/500.html', context)

Note, you will have to edit this code to reflect your app name in the import statement in urls.py and the path to your html templates in views.py.