How to enable ETag headers on Nginx for static files?

Upgrade your Nginx.

Syntax:     etag on | off;
Default:    etag on;

Context:    http, server, location

This directive appeared in version 1.3.3.

Enables or disables automatic generation of the “ETag” response header field for static resources.

Source: http://nginx.org/en/docs/http/ngx_http_core_module.html#etag