This document provides guidance on scaling Apache Kafka clusters and tuning performance. It discusses expanding Kafka clusters horizontally across inexpensive servers for increased throughput and CPU utilization. Key aspects that impact performance like disk layout, OS tuning, Java settings, broker and topic monitoring, client tuning, and anticipating problems are covered. Application performance can be improved through configuration of batch size, compression, and request handling, while consumer performance relies on partitioning, fetch settings, and avoiding perpetual rebalances.