logging proxy activity in nginx

I am using rewrite and proxy_pass and I am having some intermittent issues with the site I am proxying said rewrites too. Is there a means to log the proxy activity so I that I can debug this problem?

I am not an expert, but having the same problem here what I did in my nginx.conf :

log_format upstreamlog '[$time_local] $remote_addr - $remote_user - $server_name to: $upstream_addr: $request upstream_response_time $upstream_response_time msec $msec request_time $request_time';

access_log  /var/log/nginx/access.log upstreamlog;

The first line define a new format, and then you tell access_log to use it