v5.1.2

KNOWLEDGE BASE

Release Notes v5.1.2

Fluent Bit is a Fast and Lightweight Telemetry Agent for Linux, BSD, macOS and Windows. We are proud to announce the availability of Fluent Bit v5.1.2.

For people upgrading from previous versions, please read the Upgrading Notes section of our documentation:

https://docs.fluentbit.io/manual/5.1/installation/upgrade_notes

Fluent Bit v5.1.2 is a maintenance release that improves retry isolation, engine lifecycle reliability, metrics ingestion, and storage accounting. It also expands Google Cloud Storage authentication and formatting options, adds built-in JSON multiline parsing, and introduces namespace-aware controls for Systemd and Kubernetes workloads.

The release contains 126 commits since v5.1.1, with fixes and expanded coverage across the engine, configuration and reload paths, metrics processing, cloud outputs, storage, platform integrations, and test suite.

What’s new ?

Core

• engine: improve startup and shutdown coordination, including reliable shutdown when Fluent Bit is embedded as a library
• output retries: isolate retry payload state by route so Elasticsearch and OpenSearch can retry partial bulk failures without losing successful acknowledgements
• metrics: ingest queued and Forward metrics contexts atomically and support bounded OpenTelemetry metric batches
• configuration: validate service properties, honor environment-provided log levels alongside configuration files, and preserve relative parser paths during hot reload
• multiline: add a built-in JSON parser for multiline JSON objects and validate incomplete boundaries
• networking: recycle HTTP connections correctly and improve connection cleanup
• storage and logging: add overflow-safe accounting checks, strengthen log-suppression behavior, and release resources on initialization failures
• tests: expand engine lifecycle, hot reload, multiline, metrics batching, retry, storage-boundary, platform, and cloud-output coverage

Libraries

• cmetrics: upgrade to v2.2.2, including support for batching OpenTelemetry metric encoding by data-point limits

Plugins

Inputs

• Node Exporter Metrics
  • add macOS stat and thermal-zone metrics, expire stale network metrics, and improve collector boundary handling
• Systemd
  • add journal namespace selection when supported by the installed systemd library
• Forward
  • ingest every metrics context in batched payloads as one atomic operation
• Windows Event Log
  • handle configurations where every missing channel is intentionally ignored without terminating the process

Processors & Filters

• Kubernetes
  • support namespace-level exclusion with pod-level overrides and reject invalid override values
• Multiline
  • make the new built-in JSON multiline parser available to the filter and Tail input

Outputs

• Google Cloud Storage
  • add Application Default Credentials and Workload Identity Federation authentication
  • add Parquet compression choices and a unify_tag option for buffering multiple tags into one object
• Amazon S3
  • improve restored-buffer accounting and clean up orphaned or retry-exhausted files
• Elasticsearch and OpenSearch
  • retry only failed items from partial bulk responses while preserving delivery acknowledgements
• OpenTelemetry
  • split large metric payloads into batches that respect configured data-point limits
• Splunk
  • add time_key to select a record field for the HTTP Event Collector event timestamp
• Prometheus Remote Write
  • expire metrics that have remained stale for one hour
• Kafka
  • preserve infinite shutdown-grace configurations while continuing to honor finite grace periods
• Loki
  • isolate remove_keys accessor caches across plugin instances and improve thread-local cleanup
• Azure Blob and Azure Data Explorer
  • improve error-path cleanup and prevent authentication tokens from appearing in logs

Join us

We want to hear from you. Our community keeps growing, and you can be part of it:

• Github: http://github.com/fluent/fluent-bit
• Slack: CNCF Slack, channel #fluent-bit (https://communityinviter.com/apps/cloud-native/cncf)
• Twitter: @fluentbit