Amazon ELB not working and throwing 500 Server Error - django

Question

Created Amazon Load Balancer with 2 EC2 micro instance behind.
2 EC2 micro instances are having python services.
Services are running fine and responding while directly calling them
Services NOT running when we call them via public DNS of Load Balancer. ELB throws 500 error.
Example of Direct calling EC2 instances services:
ec2-54-200-1-2.us-west-2.compute.amazonaws.com/myservice ==> returns data
Example of calling Load Balancer:
test-12345678.us-west-2.elb.amazonaws.com/myservice ==> returns 500 error
Further points:
DJANGO property ALLOWED_HOSTS is set to ['*'] but did not work.
Using HTTP protocol i.e. Mapping Load Balancer Protocol = HTTP with port 80 to Instance Protocol = HTTP with port 80

Answer 1

I acknowledge this is a very old question but I used a solution that I believe is better and doesn't jeopardize the security of the system by setting the ALLOWED_HOSTS = ['*'].
Here's a piece of Middleware class I wrote that I feel can be reused at will.
It inherits from CommonMiddleware and it is the one who should be used instead of CommonMiddleware in the MIDDLEWARE_CLASSES setting in settings.py.
from django.middleware.common import CommonMiddleware
from django.conf import settings
from django.http.response import HttpResponse
from django.utils import importlib
class CommonWithAllowedHeartbeatMiddleWare(CommonMiddleware):
"""
A middleware class to take care of LoadBalancers whose HOST headers might change dynamically
but are supposed to only access a specific path that returns a 200-OK status.
This middleware allows these requests to the "heartbeat" path to bypass the ALLOWED_HOSTS mechanism check
without jeopardizing the rest of the framework.
(for more details on ALLOWED_HOSTS setting, see: https://docs.djangoproject.com/en/1.5/ref/settings/#allowed-hosts )
settings.HEARTBEAT_PATH (default: "/heartbeat/"):
This will be the path that is cleared and bypasses the common middleware's ALLOWED_HOSTS check.
settings.HEARTBEAT_METHOD (default: None):
The full path to the method that should be called that checks the status.
This setting allows you to hook a method that will be called that can perform any kind of health checks and return the result.
If no method is specified a simple HttpResponse("OK", status_code=200) will be returned.
The method should expect the HttpRequest object of this request and return either True, False or a HttpResponse object.
- True: middleware will return HttpResponse("OK")
- False: middleware will return HttpResponse("Unhealthy", status_code=503) [status 503 - "Service Unavailable"]
- HttpResponse: middleware will just return the HttpResponse object it got back.
IMPORTANT NOTE:
The method being called and any method it calls, cannot call HttpRequest.get_host().
If they do, the ALLOWED_HOSTS mechanism will be called and SuspeciousOperation exception will be thrown.
"""
def process_request(self, request):
# Checking if the request is for the heartbeat path
if request.path == getattr(settings, "HEARTBEAT_PATH", "/heartbeat/"):
method_path = getattr(settings, "HEARTBEAT_METHOD", None)
# Checking if there is a method that should be called instead of the default HttpResponse
if method_path:
# Getting the module to import and method to call
last_sep = method_path.rfind(".")
module_name = method_path[:last_sep]
method = method_path[(last_sep+1):]
module = importlib.import_module(module_name)
# Calling the desired method
result = getattr(module, method)(request)
# If the result is alreay a HttpResponse object just return it
if isinstance(result, HttpResponse):
return result
# Otherwise, if the result is False, return a 503-response
elif not result:
return HttpResponse("Unhealthy", status_code=503)
# Just return OK
return HttpResponse("OK")
# If this is not a request to the specific heartbeat path, just let the common middleware do its magic
return CommonMiddleware.process_request(self, request)
Of course I realize that this mechanism bypasses the CommonMiddleware altogether, but it does that only when the heartbeat path is requested, so I feel this is a little price to pay.
Hope somebody else finds it useful.