Fluentd is an open-source "unified logging layer" that collects, buffers, filters and routes log/event data between hundreds of possible data sources and destinations using a common JSON-based event format. Created in 2011 by Sadayuki Furuhashi (co-founder of Treasure Data), Fluentd joined the Cloud Native Computing Foundation as an incubating project in 2016 and graduated in 2019 — the sixth project to do so, after Kubernetes, Prometheus, Envoy, CoreDNS and containerd. It is free under the Apache 2.0 license, widely used in Kubernetes/container logging pipelines, and maintained today by a community of named maintainers backed primarily by Chronosphere (which acquired Calyptia, founded by Fluentd/Fluent Bit's creators, in 2024).