v4.2.1

Next generation Telemetry Agent for Logs, Metrics and Traces.

December 12, 2025

KNOWLEDGE BASE

Release Notes v4.2.1

Fluent Bit is a Fast and Lightweight Data Processor and Forwarder for Linux, BSD, Windows and macOS. We are proud to announce the availability of Fluent Bit v4.2.1.

Below is a detailed list of changes included in this release…

What’s new ?

Fluent Bit v4.2.1 is a maintenance release that brings enhanced Windows support with improved TLS certificate handling, Docker image enhancements including support for large page sizes, and workflow improvements. This release also includes various plugin updates, configuration documentation improvements, and stability enhancements across multiple input and output plugins.


Core


  • release: update to 4.2.1 (PR #11154)
  • workflows
    • Not to make latest on publishing 4.1 series on GitHub Releases (PR #11166)
    • Remove unused tools from unit-tests workflow for extending available disk space (PR #11184)
    • bump actions/checkout from 5 to 6 (PR #11190)
    • add new commit linter tool (PR #11245)
    • scripts: commit_prefix_check: validate only commits in active PR (PR #11245)
    • scripts: test_commit_lint: add unit test (pytest) (PR #11245)
    • bump actions/checkout from 4 to 6 (PR #11248)
    • bump actions/setup-python from 5 to 6 (PR #11249)
    • bump peter-evans/create-pull-request from 7 to 8 (PR #11275)
    • bump actions/cache from 4 to 5 (PR #11281)
  • tls
    • openssl: Implement flexible certstore loading on Windows (PR #11200)
    • openssl: Handle location prefix more strictly (PR #11200)
  • docs
    • update COMMIT_LINT.md (PR #11245)
    • COMMIT_LINT.md: update instructions for unit tests (PR #11245)
  • dockerfile
    • Docker image to support large page sizes (PR #11164)
    • allow customization of FLB_JEMALLOC_OPTIONS (PR #11164)
    • update to Debian Trixie (PR #11006)
    • install systemd libs from normal repo (PR #11006)
  • github
    • scripts: commit_linter: Extend a capability of prefix inferences (PR #11251)
    • scripts: commit_linter: Fix failing test cases (PR #11251)
  • build: prevent the toolchain from emitting an executable stack (PR #11258)

Plugins


Contributors

On every release, there are many people involved doing contributions to different areas like bug reporting, troubleshooting, documentation and coding, without these contributions from the community, the project won’t be the same and won’t be in the good shape that it is now. So THANK YOU! to everyone who takes part of this journey!

Join us

We want to hear about you, our community is growing, and you can be part of it!, you can contact us at:

Latest Version

New release on December 12, 2025

Fluent Bit v4.2.1 is out!

Check out the Release Notes, read the Updated Documentation or jump directly to the Downloads Section.

We are part of a wide community, no vendor lock-in.