Fluent Bit

Overview

Fluent Bit is a free, open-source agent for collecting and processing logs, metrics, and traces. It suits teams that want to operate telemetry infrastructure themselves, especially across constrained systems and cloud environments. Its range of pipeline tools is substantial for a self-hosted project, but compatibility needs checking at the plugin and filter level.

Key features

Fluent Bit can collect telemetry at the edge or act as a central aggregator, giving operators one agent for different stages of a pipeline. More than 100 built-in input, filter, analytics, and output plugins cover a broad set of collection and routing needs. Outputs include Splunk, Elasticsearch, OpenSearch, and Kafka; teams can also write plugins in C, Lua, Golang, or WebAssembly. This extensibility helps when standard integrations are not enough, though it rewards teams prepared to manage their own deployment.

It processes logs, metrics, and traces, with built-in parsers for JSON, Regex, LTSV, and Logfmt. Prometheus and OpenTelemetry metrics compatibility helps it fit into systems using those standards. Stream processing adds SQL queries, aggregation windows, forecasting, and data analysis, making Fluent Bit useful for more than basic forwarding.

The project is designed for high throughput with low resource consumption, a practical fit for constrained environments. Backpressure handling and memory or filesystem buffering help manage uneven delivery rates. Integrated TLS and SSL support is available for network input and output plugins. These capabilities provide useful operational safeguards, but do not remove the need to verify the support of each required plugin or filter on the target platform.

Pricing

Open-source Fluent Bit costs nothing under the Apache License 2.0 and uses self-hosted deployment. The free plan supports logs, metrics, traces, transform rules, multi-destination routing, and data enrichment. There is no paid tier to unlock those capabilities in this plan; the trade-off is that teams operate the deployment themselves and must account for platform-specific support.

Platforms

Fluent Bit supports Linux, macOS, Windows, and self-hosted deployments. Official packages and installation guidance also cover containers and selected BSD and IBM Z Linux environments. Not every plugin or filter works on BSD or every other platform, so check the specific components needed before settling on a deployment target.

Who it's for

Fluent Bit is a strong fit for operators who need a lightweight telemetry agent with broad input, processing, and output options, and who want control over where it runs. Its edge-agent and central-collector roles suit teams building pipelines across more than one environment. It is less suitable for readers seeking a managed service or a uniform plugin experience across operating systems.

Pros and cons

Pros

• Broad telemetry coverage: Logs, metrics, and traces can move through one agent, with support for Prometheus and OpenTelemetry metrics.
• Extensible pipeline: More than 100 built-in plugins, multiple output destinations, and support for custom plugins offer flexibility in collection and delivery.
• Free and permissively licensed: Apache License 2.0 and self-hosted deployment make the project available without a paid plan.
• Designed for constrained systems: High throughput and low resource consumption align with edge and resource-limited deployments.

Cons

• Platform support varies: Some plugins and filters are not supported on BSD or every other platform, which can constrain otherwise portable pipelines.
• Self-hosted operation: Teams must run and manage the agent deployment themselves rather than choosing a managed plan.

Alternatives

Edge Delta is worth considering for teams interested in a freemium alternative with a free plan and a 14-day free trial.

Bindplane may suit teams that want a free plan with stated limits of one user, 10 projects, and 100 GB/day of combined telemetry, alongside unlimited collectors.

Cribl Edge offers a free plan capped at 1 TB/day, 100 Edge Nodes, and one Fleet, making those explicit capacity limits useful for comparison.

Honeycomb is an alternative for teams looking for a free plan capped at 20 million events and 100 million metric data points per month, with two triggers.

syslog-ng is another free, open-source option, with an open-source edition under GPL/LGPL licensing.

Tenzir offers a community plan with 1 TB/day ingress and 1 TB edge storage for teams comparing against a project with stated capacity allowances.

AWS Distro for OpenTelemetry is a free option for readers looking at an OpenTelemetry-focused project that contributes enhancements and fixes upstream.

Cribl Stream is another freemium option, with a free plan allowing up to 1 TB/day and unlimited pipelines and routes.

Verdict

Choose Fluent Bit if you want a free, self-hosted agent that combines telemetry collection, processing, and routing across edge and central deployments. Its plugin breadth and support for logs, metrics, and traces are the main reasons to choose it. Look elsewhere if you need managed operation or depend on plugins and filters whose support is uneven across your target platforms.