Lesson 8

When replicas don't help

Break it

This app is mostly writes. Turn traffic up to 3,000 requests per second, then add read replicas.

Users

1,000 req/s

Load balancer

splits evenly

2%

App servers

× 4

26%

Cache

Not added

Off

DB primary

reads + writes

70%

Read replicas

None

Off

Traffic1,000 req/s

Read replicas0

p50 latency

174 ms

Failed requests

0.0%

Monthly cost

$320