The classic configuration format is Fluent Bit’s section-based notation for defining services, inputs, filters, and outputs. It resembles a Fluentd configuration file and remains important for compatibility with Fluent Bit’s established install base, although YAML is becoming the preferred direction for newer features. section 2.2 section 2.2.2
Use these rules when writing a classic-format file:
- Place section directives such as [SERVICE], [INPUT], [FILTER], and [OUTPUT] at the left margin; declaration case is insignificant. section 2.2.2
- Indent each section property consistently, using spaces rather than placing the property and value on separate lines. section 2.2.2
- Repeat [INPUT] or [OUTPUT] blocks to define multiple sources or destinations, and assign tags or output formats as needed. section 2.2.2
Minimal classic-format pipeline
A small configuration can emit dummy records to standard output: [service] flush 1 [input] name dummy dummy {"hello":"my world"} tag dummy1 [output] match * name stdout Run it with `fluent-bit -c hello-world.conf`. The same pipeline can be represented in YAML, but classic notation keeps the service, input, and output blocks visually direct.
