I have an nginx loadbalancer which just proxies requests to a few upstream servers.
Now, what I would like to do is:
For one out of ten requests, I want to measure the response time of nginx (in milliseconds) and forward that value to an InfluxDB metric database.
I'm not sure how I can make this work. My initial idea was to leverage the "access_by_lua_block" functionality, but if I understand correctly, this is executed before the request is sent to the upstream server. Is there a way to execute lua-code after a response is received from the upstream server?
Just to be clear: I want to the response time of the nginx loadbalancer itself, not of the upstream application server. My final goal is to compare the response times of the loadbalancer with the response times of the upstream servers, to identify potential bottlenecks in the loadbalancer configuration.