What do HTTP cache statuses mean?
$upstream_http_x_cache status can be either "MISS”, “BYPASS”, “EXPIRED”, “UPDATING”, or “HIT”.
MISS - the content is not found in cache. It will get the content from the origin, cache it, and return the content.
BYPASS - no caching, it get the content straight from the origin.
EXPIRED - cache time limit reach, but no content change on origin.
UPDATING - cache time limit reach, cache getting new content change on origin.
HIT - the content is found in cache, it return the content from the cache.