"Purge all" is not a deploy step

"Purge all" is not a deploy step
A Stockholm fashion site purged their entire CDN cache on every deploy, ten times a day, thinking a clean slate was safer. Each purge dumped 200k objects, and the cold cache crushed their origin for 20 minutes after.
The myth: full purge guarantees correctness. The reality: 99% of those objects hadn't changed, and the stampede of misses doubled their cloud bill.
What we changed: we switched to tag-based purging. Each deploy purged only the cache tags for changed templates, leaving the rest warm.
Result: post-deploy origin load flatlined, cache-hit ratio stayed above 90% through deploys, and their monthly origin egress dropped by $1,400.
Surgical purges beat scorched earth. Invalidate what changed, nothing else.
The number that mattered: $1,400/month saved on origin egress.