Improve logging

[exussum12]

Currently its almost impossible to know which host actually handled the request, this extra variable logs the upstream server too

[buchdag]

Hi ! Thanks for the PR !

Do you have a before PR / after PR example of the log ?

[exussum12]

Sure.
Easiest to set up scenario is

Terminal 1
docker run -p 80:80 -v /var/run/docker.sock:/tmp/docker.sock:ro jwilder/nginx-proxy

Terminal 2
docker run -e VIRTUAL_HOST=test.local nginx:latest

Terminal 3
docker run -e VIRTUAL_HOST=test.local nginx:latest

The proxy will load balance between the two
Terminal 4

curl 127.0.0.1 -H "Host: test.local"
curl 127.0.0.1 -H "Host: test.local" 

One request is served by each and the resulting logs are

nginx.1    | test.local 172.17.0.1 - - [11/Jun/2021:10:09:37 +0000] "GET / HTTP/1.1" 200 612 "-" "curl/7.74.0"
nginx.1    | test.local 172.17.0.1 - - [11/Jun/2021:10:09:41 +0000] "GET / HTTP/1.1" 200 612 "-" "curl/7.74.0"

After this change

nginx.1    | test.local 172.17.0.1 - - [11/Jun/2021:10:14:41 +0000] "GET / HTTP/1.1" 200 612 "-" "curl/7.74.0" "172.17.0.4:80"
nginx.1    | test.local 172.17.0.1 - - [11/Jun/2021:10:14:42 +0000] "GET / HTTP/1.1" 200 612 "-" "curl/7.74.0" "172.17.0.3:80"

The last param makes it easier work see where the request ended up.

I added to the end to prevent breaking any existing awk scripts which people have have written

[buchdag]

Seems okay to me, I have no objection to merging this but I'm a bit concerned by people relying on load balancing with nginx-proxy. This was never intended as a feature, is untested and kinda just work "by accident".

[exussum12]

Its not just load balancing it helps with, another use case is confirming you are going to the correct container in a default fall back. Eg nginx doesn't match as expected, and serves the default vhost instead.

The load balancing case just makes it clear that the number changes.