GCP load balancer 502 server error and "backend_connection_closed_before_data_sent_to_client" IIS 10

Question

I have GCP load balancer with 4 IIS 10 web servers. Sporadically it comes with 502-Server error. In the logs it shows it is because of backend_connection_closed_before_data_sent_to_client. I have read thru the article https://cloud.google.com/compute/docs/load-balancing/http/ and it says keepalive timout need to be set to 620 seconds for nginx and apache. How do I do the same in IIS 10.

Faith

Answer 1

Figured this out after raising a ticket google cloud team. I am putting it here so that others can benefit.

Step 1 : Set the timeouts in Google Cloud Load Balancer

There are two timeout settings in Google cloud load balancer.

1. Timeout and
2. Connection draining timeout.

See the screenshot below.

Both the above settings need to be the same. In our case, there are a number of long running requests and it is set to 1800 seconds.

Step 2: Set the connection timeout in IIS 20 second greater than the load balancer setting

Under IIS Site name - go to Advanced settings and then set the Connection Time-out value to 20 seconds more than the load balancer timeout. In my case 1820.

The idea is that the IIS connection should not timeout before load balancer. If it times out then it may leads to backend_connection_closed_before_data_sent_to_client error.

Faith

Answer 2

You can set this in web.config as execution time out attribute in http runtime by default when you set keep alive it sets time out to 120 seconds .If still doesn’t work then may be there is proxy server between your request response process . You have to check that proxy server time out.

I faced the same scenario in gcp and I have setted everything in load balancer level but did not work . Then I found that there was an proxy server between our process . Let me know if you can tell in more detail

Traweek

What is that web.config settings and it should be applicable to IIS 10. – Faith

You might need to check this thread, where they discussed about changing the Keep-alive value on IIS. See if that helps you – Aggressive