Enhancing resiliency in opensearch clusters: An in-depth technical exploration of Admission Control

This post details the implementation and benefits of OpenSearch's Admission Control feature for enhancing cluster resiliency. It explains the 'Why Admission Control?' and 'What is Admission Control?' aspects, including its role in rate-limiting requests based on resource utilization (CPU and IO). The technical breakdown covers the default settings, the three modes (DISABLED, MONITOR, ENFORCED), and provides detailed instructions on how to enable and configure admission control at different levels (transport, CPU/IO override, and specific limits for indexing/search). It also includes sample rejection responses and node stats API output, and discusses strategies for handling rejected requests, such as retries and Dead Letter Queues. The post demonstrates Atlassian's experience with admission control, showing improved search reliability during high indexing loads.