The Amazon Builders' Library is a collection of articles written by principal engineers at Amazon that explain how Amazon builds scalable and resilient systems. The library focuses on various topics, including avoiding insurmountable queue backlogs, which is the main topic of the latest article in this series. To measure availability and latency for SQS, metrics such as the number of messages going into the dead-letter queue (DLQ) are used to gauge availability, while message age can be used to measure latency. In multi-tenant systems, fairness throttling is crucial to prevent a single customer from monopolizing resources and affecting other customers' workloads. Amazon's strategies for building multi-tenant systems include separating workloads into separate queues, shuffle-sharding, sidelining excess traffic, and dropping old messages by specifying message time-to-live. These strategies aim to avoid backlogs, limit threads and resources per workload, send backpressure upstream, and use delay queues to put off work until later.