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 bes

Answer 1

Old question, new answer suitable for nginx verions 1.3.8, 1.2.5 and above.

You can use a combination of $connection and $connection_requests now. Just define your own variable in the server block:

server {
    ...
    set  $trace_id  $connection-$connection_requests;
    ...
}

This id is going to be unique across nginx unless the server gets restarted.

$connection - The connection serial number. This is a unique number assigned by nginx to each connection. If multiple requests are received on a single connection, they will all have the same connection serial number. Serial numbers reset when the master nginx process is terminated, so they will not be unique over long periods of time.

$connection_requests - The number of requests made through this $connection.

Then, in your location block, set the actual trace ID:

location / {
    ...
    proxy_set_header X-Request-Id $trace_id;
    ...
}

Bonus: Make $trace_id unique even after server restarts:

set  $trace_id  $connection-$connection_requests-$msec;

$msec - The current unix timestamp in seconds, with millisecond resolution (float).