This week in caching: full-page cache vs personalization — the real tradeoffs

This week in caching: full-page cache vs personalization — the real tradeoffs

When 'cache the whole page' meets 'but the header shows the username':

— Cache + ESI/fragment holes: cache the page, punch out dynamic blocks via Edge Side Includes or AJAX. Best when 95% is shared and only a sliver is per-user.
— Vary-by-cookie: cache separate copies per segment. Fine for 2-3 audiences (guest/member/admin); cache-explosion disaster if you Vary on a unique session ID.
— Cookie stripping at the edge: drop tracking/analytics cookies before the cache key so anonymous users actually share a cache entry — the single biggest hit-rate fix on most sites.

The failure mode everyone hits: not normalizing cookies, so every visitor gets a unique cache key and your hit rate sits near zero while you wonder why caching 'does nothing'.

Bookmark: Fastly's ESI vs edge-personalization guide.