This document provides an introduction to Apache Kafka. It begins with an overview of Kafka as a distributed messaging system that is real-time, scalable, low latency, and fault tolerant. It then covers key concepts such as topics, partitions, producers, consumers, and replication. The document explains how Kafka achieves fast reads and writes through its design and use of disk flushing and replication for durability. It also discusses how Kafka can be used to build real-time systems and provides examples like connected cars. Finally, it introduces Apache Metron as an example of a cyber security solution built on Kafka.