Setting a trace id in nginx load balancer

Question

I'm using nginx as a load balancer in front of several upstream app servers and I want to set a trace id to use to correlate requests with the app server logs. What's the best way to do that in Nginx, is there a good 3rd party module for this?

Otherwise a pretty simple way would be to base it off of timestamp (possibly plus a random number if that's not precise enough) and set it as an extra header on the request, but the only set_header command I see in the docs is for setting a response header.

Answer 1

nginx 1.11.0 added the new variable $request_id which is a unique identifier, so you can do something like:

   location / {       proxy_pass http://upstream;       proxy_set_header X-Request-Id $request_id;    } 

See reference at http://nginx.org/en/docs/http/ngx_http_core_module.html#var_request_id

Answer 2

In most cases you don't need a custom module, you can simply set a header with a combination of embedded variables of http_core_module which is (most probably) unique. Example:

  location / {       proxy_pass http://upstream;       proxy_set_header X-Request-Id $pid-$msec-$remote_addr-$request_length;   } 

This would yield a request id like "31725-1406109429.299-127.0.0.1-1227" and should be "unique enough" to serve as a trace id.