Instead of re-downloading uncacheable documents, users can get a lightweight 304 Not Modified response regardless of which server they hit.
For that, the documents must respond with the same
Last-Modified time header from all servers. The same
applies when using the
ETag header on Nginx as it generates them using that time.
For preserving modification times, deploy copying over with
By the way, send a
response header too. It prevents Chrome® from sometimes
showing a 304 with a stale page. For example, when restoring a
session, or when offline without a registered service worker.