How does Redis + Varnish + FPC work together?

Three layers, each handling different traffic. Varnish sits in front of Magento, it caches full HTML for cacheable pages (category, PDP, CMS) and serves them in < 50ms without ever waking up PHP. FPC (Full Page Cache) is Magento’s own page cache, used as a fallback when Varnish misses. Redis handles two separate jobs: (a) the default-cache for config, layout, blocks, and (b) PHP session storage. We tune all three: Varnish VCL with hole-punching for cart/customer state, FPC tag invalidation, Redis maxmemory + eviction policy, separate Redis databases for cache vs sessions. Done right, your origin only sees logged-in / cart traffic, everything else is served from cache.