Fluentd and Fluent Bit are open-source tools developed by Treasure Data to streamline logging processes in distributed environments, particularly for Kubernetes and Docker. Fluentd, established in 2011 and written in Ruby, is a log aggregator that unifies and processes data from multiple sources into JSON objects, emphasizing scalability and resilience with a wide array of plugins. Fluent Bit, introduced in 2015 and written in C, is designed for high-performance environments with limited resources, acting primarily as a log forwarder with a smaller footprint and plugin ecosystem. While Fluentd handles heavy throughput and complex aggregation tasks, Fluent Bit excels in lightweight data collection and delivery, often serving as an edge device agent. Together, they form an efficient logging pipeline where Fluent Bit collects and forwards data to Fluentd for processing and routing. The growing adoption of Kubernetes bolsters their use, with Fluent Bit's lightweight nature complementing Fluentd's robust capabilities, enhancing observability in modern IT infrastructures.