[dahumpty]

Its interesting to note that the the boweb-production servers of "www" don't have read-replicas (asynchronous replication) for read scalability. Anyone know why? Typically, one would use read-replicas to alleviate read workloads on the master.

[ceejayoz]

Most likely the www servers are serving almost entirely static, cached content. Hell, they might not actually see any actual public traffic - they might just serve as CDN origins.

[scottvdp]

This is 100% correct. We also generated static snapshots of the origin and mirrored to S3. In the instance of something going awry with our primary origin servers, we could fail back to S3 as an origin.

EDIT: I'll add that our origin offload for WWW hovered around 98%.