The blog network where a tracking cookie killed every cache

The blog network where a tracking cookie killed every cache

A portfolio of 60 niche blogs ran on one WordPress multisite. Pageviews were healthy but the edge hit ratio sat at 12%. Every visitor got a session cookie set on the homepage, and the CDN's default rule treated any request carrying a cookie as uncacheable. So almost nothing cached.

The content was static. The cookie was the saboteur.

What we changed: added an edge rule to ignore cookies on all GET requests to non-admin paths, and stripped the Set-Cookie header from cacheable responses so the edge would store them. Logged-in /wp-admin paths stayed bypassed.

Hit ratio jumped from 12% to 96% in a day. Origin requests fell from 1.4M/day to 90k. TTFB in Chicago dropped from 410ms to 24ms, and the shared host's load average fell from 6.2 to 0.8.

The number that mattered: hit ratio 12% to 96%.