gocrazy

Systems · Week 3

CDN for live and near-live media

Session 1 2 min read 2h

Cache hierarchies, signed paths, and origin shield patterns for media.

signed-urls soft-ttl

CDN for live and near-live media

Business constraint

Live commentary clips and thumbnails hit a global audience. Origin egress is expensive and fragile.

Naive v0

Every player hits origin. Or cache forever and serve wrong clip after edit. Unsigned URLs leak.

Failure drill

Origin bandwidth cliffs. Cache stampedes on popular clip keys. Hotlinking drains budget. Stale takedown content remains public.

Evolution path

Iteration 1

CDN with short TTL + soft purge. Origin shield to collapse regional misses. Separate cache keys for variants.

Iteration 2

Signed URLs with expiry for private or licensed media. Rotate signing keys with overlap.

Iteration 3

Drill purge and stampede: ensure single-flight at origin shield.

Implementation cut

Treat CDN as part of the miss-control system. Document purge authority and signing key ops.

Numbers

Origin offload %. Purge propagation time. Unauthorized fetch rate after expiry.

Pattern tags

Self-check

  1. What is an origin shield for?
  2. Why soft TTL on media?
  3. How do signed URLs fail closed?
  4. What belongs in the cache key?
  5. How do you drill a takedown?

Walkthrough

Recordings will appear here when published. Until then, work the failure drill and lab locally — pause after each iteration and write the metric that moved.