Apache load balancer logging question
You can use the Custom log format to do that. One way I think you can do is to add the environment variable to the log.
mod_proxy_balancer (that I suppose you are using) exports BALANCER_WORKER_NAME variable that is the name of the Worker used for the request. You can use the %{BALANCER_WORKER_NAME}e directive on your Custom Log format string to get that logged. This is an example of the default debian 'combined' log format with the directive added:
LogFormat "%h %l %u %t \"%r\" %>s %b \"%{Referer}i\" \"%{User-Agent}i\" \"%{BALANCER_WORKER_NAME}e\"" combined