Another simple solution would be to write a custom MIDDLEWARE which will give the response to ELB before the ALLOWED_HOSTS is checked. So now you don't have to load ALLOWED_HOSTS dynamically.

The middleware can be as simple as:

project/app/middleware.py

from django.http import HttpResponse
from django.utils.deprecation import MiddlewareMixin

class HealthCheckMiddleware(MiddlewareMixin):
def process_request(self, request):
if request.META["PATH_INFO"] == "/ping/":
return HttpResponse("pong")

settings.py

MIDDLEWARE = [
'corsheaders.middleware.CorsMiddleware',
'app.middleware.HealthCheckMiddleware',
'django.middleware.security.SecurityMiddleware',
'django.contrib.sessions.middleware.SessionMiddleware',
'django.middleware.common.CommonMiddleware',
'django.middleware.csrf.CsrfViewMiddleware',
...
]

Django Middleware reference https://docs.djangoproject.com/en/dev/topics/http/middleware/