Highly Available, Fault-Tolerant Pull Queries in ksqlDB

What this post added

This post details the engineering efforts to make pull queries remain highly available in the face of server failures by implementing faster failure detection via heartbeating and enabling lag-aware routing to standby replicas, allowing ksqlDB to operate as an AP system under certain conditions. It explains the trade-offs between CP and AP systems using the CAP and PACELC theorems, and describes the implementation of a ksqlDB server mesh for heartbeating and the use of KIP-535 for standby routing and lag-aware routing.