Fluentd is a dominant observability-data collector in the Fluent ecosystem. Its pluggable integrations make it useful for connecting varied sources and targets, gathering logs and metrics, and preparing data for tools that render or analyze it. section 1.3 section 1.1.2
Fluentd and Fluent Bit are complementary rather than mutually exclusive. They communicate seamlessly, including through the forward plugin, so deployments can blend both tools or migrate gradually. Fluentd remains particularly suited to non-cloud-native environments with broad adapter needs and accessible custom-plugin skills. section 1.3 section 1.4 section 3.9
A Fluentd pipeline can be understood through its configuration directives:
- `<system>` sets node-wide behavior, such as the log level. section 2.2.1
- `<source>` defines an input, such as a Dummy source that emits `{"hello": "my world"}`. section 2.2.1
- `<match *>` routes matching events to an output; the example sends every event to stdout. section 2.2.1
Minimal stdout pipeline
A small Fluentd configuration can set `log_level info`, create a Dummy input, and match all tags to the stdout output. It demonstrates the basic flow: generate an event, match it, and write it to the console. section 2.2.1
Table 2.4 Classic Fluent Bit vs. Fluentd configuration comparison
|
Classic Fluent Bit
|
Fluentd
|
|---|---|
[SERVICE]
flush 1
daemon Off
log_level info
# define the Dummy source
[INPUT]
name Dummy
dummy {"hello": "my world"}
# Accept all log events regardless of tag and write
# them to the console
[OUTPUT]
name stdout
match *
|
<system>
log_level info
</system>
# define the Dummy source
<source>
@type Dummy
dummy {"hello": "my world"}
</source> # after a directive
# Accept all log events regardless of tag and write them to the console
<match *>
@type stdout
</match>
|
Compare Fluentd’s XML-style directives with Fluent Bit’s bracketed configuration syntax when planning coexistence or migration. section 2.2.1
For Kubernetes-centered and containerized deployments, Fluent Bit is described as the lighter choice and has OpenTelemetry support. Fluentd is not therefore automatically legacy: selecting between them depends on architecture, existing adapters, and operational constraints. section 1.4 section 1.3.5
