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I have set up an Nginx server to proxy requests between certain IP and an App Engine app. With one instance everything worked as expected, the requests when through etc.

But, when I setup an Instance Group using the image as before to create the instances in the group my App Engine app gets requests from those instances even when I don't send traffic there. They're just accessed on / path and /nginx_status path, each 2-3 seconds.

What could be causing this behavior? How instances in group are different than "solo" instances?

EDIT: this behavior only happens when there's a load balancer in place, without the load balancer the servers behave as expected.

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  • Are you using load balancer for your instance group? – Kamran Jan 10 '16 at 21:24
  • I did at first, but I turned it off to see if it's what's causing the problem. So no load balancer now. – MeLight Jan 11 '16 at 08:13
  • Ok, just looked now, I had a partially configured load balancer. Why would it keep pinging the servers in the instance group though? – MeLight Jan 11 '16 at 08:40
  • Load Balancer sends health check requests to each instance at the specified frequency: https://cloud.google.com/compute/docs/load-balancing/health-checks – Kamran Jan 13 '16 at 02:56
  • @Kamran thanks for input. The doc doesn't say much about the url of the check. Is there a way to tell that it was health check from the logs? – MeLight Jan 13 '16 at 13:40
  • If you're using HTTP(S) Load balancer, both external and health check requests will hit the web server from 130.211.0.0/22 range as source IP addresses. Thus, distinguishing the external and health check traffic will be difficult through the source IP address. However, you can run the web server on multiple ports; one of the ports will be dedicated for the health-check. Configure the health check to use that port, and then you can filter the health check traffic on your proxy using the destination port. – Kamran Jan 14 '16 at 00:04
  • http://serverfault.com/questions/655067/is-it-possible-to-make-nginx-listen-to-different-ports?answertab=votes#tab-top – Kamran Jan 14 '16 at 00:05

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