docs: administration: hot-reload: document relative path resolution (#2700)

Document how Fluent Bit resolves relative file references and the hot reload fix from fluent-bit d94fd89ce.

Add a Relative paths section listing the references this affects: parsers_file, plugins_file, upstream high availability files, and the stream processor streams_file
Describe the two-step resolution: the path as written relative to the process working directory first, then the directory holding the main configuration file
Note that absolute paths are used as provided and aren’t retried
Record that Fluent Bit 5.1.3 and greater preserves the configuration directory across a hot reload, that earlier versions lost it, and that absolute paths are the workaround on those versions
Document that a failure to preserve the directory halts the reload, keeps the previous configuration running, and logs a specific message

Signed-off-by: Eric D. Schabell eric@schabell.org

description: High Performance Telemetry Agent for Logs, Metrics and Traces

Fluent Bit documentation

Fluent Bit is a fast and lightweight telemetry agent for logs, metrics, and traces for Linux, macOS, Windows, and BSD family operating systems. Fluent Bit has been made with a strong focus on performance to allow the collection and processing of telemetry data from different sources without complexity.

Features

High performance: High throughput with low resources consumption
Data parsing
- Convert your unstructured messages using Fluent Bit parsers: JSON, Regex, LTSV and Logfmt
Metrics support: Prometheus and OpenTelemetry compatible
Reliability and data integrity
- Backpressure handling
- Data buffering in memory and file system
Networking
- Security: Built-in TLS/SSL support
- Asynchronous I/O
Pluggable architecture and extensibility: Inputs, Filters and Outputs:
- Connect nearly any source to nearly any destination using preexisting plugins
- Extensibility:
  - Write input, filter, or output plugins in the C language
  - Wasm: Wasm Filter Plugins or Wasm Input Plugins
  - Write Filters in Lua or Output plugins in Golang
Monitoring: Expose internal metrics over HTTP in JSON and Prometheus format
Stream Processing: Perform data selection and transformation using basic SQL queries
- Create new streams of data using query results
- Aggregation windows
- Data analysis and prediction: Time series forecasting
Portable: Runs on Linux, macOS, Windows and BSD systems

Release notes

For more details about changes in each release, refer to the official release notes.

If you are upgrading from the Fluent Bit 4.2 series, start with What’s new in Fluent Bit v5 and Upgrade notes.

Fluent Bit, Fluentd, and CNCF

Fluent Bit is a CNCF graduated sub-project under the umbrella of Fluentd.

Fluent Bit was originally created by Eduardo Silva and is now sponsored by Palo Alto Networks. As a CNCF-hosted project, it’s a fully vendor-neutral and community-driven project.

License

Fluent Bit, including its core, plugins, and tools, is distributed under the terms of the Apache License v2.0.