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Fluentd vs Fluent Bit: How to Choose in 2024

Better Stack Team
Updated on February 2, 2024

Centralizing logs, rather than manually navigating through them on individual systems, is widely recognized as an efficient strategy for log analysis. This process is simplified using log collectors that efficiently collect logs from various sources and direct them to a chosen destination for thorough log management.

The real challenge arises in selecting an appropriate log collector. Fluentd and Fluent Bit are prominent contenders within this domain, each with distinct advantages.

This article will provide a detailed comparison of Fluentd and Fluent Bit, exploring their advantages, limitations, and advising on scenarios where one might be more appropriate than the other.

Let's get started!

What is Fluentd?

Fluentd, developed by Treasure Data in 2011, is an open-source, vendor-neutral log collector designed to collect, process, and route logs from various sources to multiple destinations. Its key strength is its flexibility, supporting numerous sources and destinations through its extensive library of over 1000 built-in and third-party plugins. This flexibility is partly due to its pluggable architecture and the use of a high-level language like Ruby, which encourages community contribution.

Notably, Fluentd is recognized for its reliability, featuring mechanisms like memory and file-based buffering to prevent data loss during heavy log generation. It's also scalable for high-volume environments, with configurations available for high availability to handle increasing log demands. This robustness has garnered trust from over 5000 companies worldwide, including major players like Atlassian, AWS, and Microsoft.

Screenshot of FluentD

Learn more: How to Collect, Process, and Ship Log Data with Fluentd

What is Fluent Bit?

Fluent Bit, developed by the same team behind Fluentd at Treasure Data, is an open-source, vendor-neutral log collector designed explicitly for lightweight and resource-constrained environments such as Embedded Linux, Gateways, and containerized ecosystems. Like Fluentd, Fluent Bit is adept at collecting, processing, and routing logs from various sources to different destinations.

Written entirely in C, Fluent Bit is engineered for performance and minimal resource usage. It features a pluggable architecture and offers over 100 plugins. It is noted for its efficiency, reliability, and includes mechanisms for handling backpressure and buffering data in both memory and filesystems to prevent data loss. Fluent Bit is also compatible with a vendor-neutral approach to metrics, allowing integration with systems like Prometheus and OpenTelemetry.

Screenshot of Fluent Bit diagram

Learn more: How to Collect, Process, and Ship Log Data with Fluent Bit

Now that we have a fundamental understanding of Fluentd and Fluent Bit, let's compare these two tools. Our evaluation will be structured around the following key criteria:

# Feature Fluentd Fluent Bit
1 Supported platforms ✔✔ ✔✔
2 Memory usage/performance ✔✔
3 Ecosystem and plugins ✔✔
4 Log parsing ✔✔ ✔✔
5 Event routing ✔✔ ✔✔
6 Transport ✔✔ ✔✔
7 UI & UX design ✔✔
8 Pricing ✔✔ ✔✔

✔ - partial or limited feature

✔✔ - complete feature

1. Supported platforms: Fluent Bit wins

Fluentd is designed using a mix of C and Ruby, with the core and plugins primarily in Ruby, while performance-critical elements like event buffering and low-level I/O operations are in C for enhanced efficiency. This architecture provides solid performance with reasonable resource use. Fluentd is versatile, running on Linux, Windows, and macOS, and its Apache License v2.0 allows for flexibility in deployment as an aggregator or forwarder.

In contrast, Fluent Bit is entirely written in C, ensuring it's lightweight and dependency-free, drawing on the experience gained from developing Fluentd. It can also function as an aggregator and forwarder and is compatible with Linux, Windows, and macOS. Fluent Bit excels with its integration in embedded systems and containers, making it an ideal choice for environments where resources are limited.

While both tools offer cross-platform support and flexibility under the Apache License v2.0, Fluent Bit stands out for its broader suitability, especially in embedded systems and containers, making it the more versatile option for various platforms.

2. Memory Usage/Performance: Fluent Bit wins

Fluentd and Fluent Bit were designed with distinct purposes in mind. Fluent Bit, in particular, is optimized for environments with limited resources like embedded systems or containers. It's recognized for its lightweight design and resource efficiency, with a single instance using less than 1MB, thus maintaining a low memory footprint. This efficiency is attributed to its exclusive use of the C language, renowned for its speed.

On the other hand, Fluentd tends to use more memory, with a single instance typically needing about 40MB. This increased demand is largely due to its extensive use of Ruby, a language known for consuming more memory. This aspect means that while Fluentd is robust, it may not match Fluent Bit's performance levels, even though parts of it are written in the more efficient C language.

When it comes to handling large volumes of logs and scalability, both Fluentd and Fluent Bit are competent. However, Fluent Bit offers optimal efficiency and speed in scenarios where performance and minimal memory usage are crucial.

3. Ecosystem and Plugins: Fluentd wins

Fluentd boasts an extensive ecosystem of plugins that significantly enhance its functionality. These plugins expand Fluentd's support for diverse inputs and filtering sources. The fact that Fluentd's core components are written in Ruby contributes to the ease with which the community of contributors can develop and maintain plugins, often housed in their dedicated repository.

Given Fluentd's more extended presence in the field, its plugin library has flourished to encompass over 1000 plugins. This extensive collection, including many user-contributed options such such as fluent-plugin-anonymizer, fluent-plugin-geoip, and kinesis. All of these are readily available through Fluentd's official plugin page.

Fluent Bit diagram showing the pluggable architecture

Conversely, Fluent Bit boasts a collection of over 100 plugins, organized into categories like input, parsers, filters, and output. Despite its substantial offerings, this library doesn't quite match the breadth found with Fluentd. Moreover, contributing to Fluent Bit's ecosystem might be more challenging due to the need for proficiency in C, a language often perceived as more complex and demanding, especially regarding memory safety.

For users prioritizing a vast and versatile ecosystem with a wide range of plugins, Fluentd is the clear winner, offering an extensive library and a more accessible platform for community contributions.

4. Log parsing: Tie

Fluentd and Fluent Bit excel in log parsing capabilities, offering robust built-in parsers that efficiently handle both structured and unstructured logs without additional plugins.

Fluentd's comprehensive parsing capabilities support various formats, including JSON, regex, and msgpack. It's adept at parsing logs from widely-used platforms such as Nginx, Apache, and Syslog, making it a versatile choice for diverse log management needs.

Similarly, Fluent Bit has a powerful built-in parser set. It efficiently handles structured and unstructured data, with capabilities to parse JSON, regular expressions, and predefined formats from familiar sources like Apache, Nginx, Docker, and Syslog.

In log parsing, they stand as equals, as both Fluentd and Fluent Bit demonstrate the capability to parse logs in common formats without needing third-party support.

Screenshot of Fluent bit parser

5. Event Routing: Tie

Event routing defines the behavior of log forwarding or aggregation to direct log events or data to specified destinations or filters. Both Fluentd and Fluent Bit shares this strength. Both platforms exhibit identical routing capabilities.

The process involves tagging each incoming log from the inputs. These tags are then leveraged to apply routing rules. For instance, logs tagged as "file-logs" can be directed to a destination like a file on the file system, while logs with different tags are forwarded to alternative destinations.

This tagging mechanism is highly efficient, simplifying the routing process compared to other log forwarders that rely on complex if-then-else statements. The tagging approach employed by Fluentd and Fluent Bit is a testament to its effectiveness in managing and routing logs, resulting in a tie between the two platforms in this aspect.

screenshot of Routing in fluent bit

6. Transporting Data: Tie

When transporting data, both Fluentd and Fluent Bit offer output plugins that effectively collect logs from sources and forward them to diverse destinations, including consoles, cloud storage services, local files, and more.

A crucial feature common to both is their configurable buffering system, which temporarily holds log events. This buffer can be set to operate in memory, creating an in-memory queue, or on the disk as files. This buffering mechanism is critical to ensuring data persistence, offering a safety net for log data that allows for retrieval and reprocessing in cases of system restarts or unexpected interruptions.

Ultimately, neither Fluentd nor Fluent Bit takes a distinct lead in transporting data. Both are robust solutions with the tools to ensure data persistence and reliability during log collection and forwarding.

7. User interface: Fluentd wins

Fluentd differentiates itself by offering a user-friendly, web-based user interface that significantly simplifies log data management. This dashboard allows users to monitor logs and metrics and manage configurations effortlessly. It further enhances user experience by enabling the installation, uninstallation, and upgrading of Fluentd services, as well as facilitating essential operations like start and restart:

screenshot of Fluentd interface

In contrast, Fluent Bit does not currently provide a user interface. The existence of an open GitHub issue (#2147) underscores the community's desire for a web UI and marks a notable gap in Fluent Bit's offerings.

Given this disparity, Fluentd holds the upper hand for users who prioritize a robust and intuitive user interface for managing their log data efficiently.

8. Pricing: Tie

Both Fluentd and Fluent Bit stand on equal footing regarding pricing, as they are both available as free and open-source software under Apache License 2.0. Additionally, they have both been acknowledged and graduated by the Cloud Native Computing Foundation, with Fluent Bit notably recognized as a graduated project within the Fluentd ecosystem.

The open-source nature of these tools means users can use them without any subscription fees or hidden costs, providing a vendor-neutral option that doesn't lock users into a specific platform or service.

While users might seek additional services for storing, managing, or analyzing logs from third parties like Better Stack, which may incur costs beyond certain usage limits, the fundamental use of Fluentd and Fluent Bit remains entirely free. Therefore, in terms of direct costs for using the core tools themselves, Fluentd and Fluent Bit are the same, resulting in a tie in pricing.

Aggregating your logs with Better Stack

Once you've picked the tool that works best for you, you'll need to route your logs to a centralized platform for monitoring, storage an analysis.

Better Stack is a robust log management tool that aggregates logs from Fluentd and Fluent Bit. It offers advanced functionalities for parsing, filtering, analyzing, and correlating logs, which is particularly valuable when handling large volumes of data.

Better Stack can be integrated with either Fluentd or Fluent Bit. Below are examples of how to configure each for integration with Better Stack:

For Fluentd:

  @type tail
  path /var/log/logify/app.log
  pos_file /var/log/fluent/file.log.pos
  tag file.logs
  format none

<match file.logs>
  @type logtail
  @id output_logify_logtail
  source_token <your_logify_source_token>
  flush_interval 2 # in seconds

For Fluent Bit:

    Name         tail
    Path         /var/log/logify/app.log
    Tag          filelogs

    name    http
    match   filelogs
    tls     On
    port    443
    uri     /
    header  Authorization Bearer <your_logify_source_token>
    header  Content-Type application/msgpack
    format  msgpack
    retry_limit 5

Once you're logs start coming through, you will see them in the live tail page:

Screenshot of Live tail in Better Stack

From there, you can create dashboards to visualize and monitor your data. You also have the ability to set up customized alerts and notifications through various channels such as phone, email, or webhooks, ensuring you're promptly alerted to any critical log-related events:

Screenshot of Better Stack configured with the necessary options

An outstanding feature of Better Stack is its ability to alert users to irregularities within their logs, enhancing the overall monitoring and security posture. Despite its advanced features and integration capabilities, Better Stack remains affordable, making it an attractive alternative for comprehensive log management.

In summary, while Fluentd and Fluent Bit are exceptional at log collection and forwarding, Better Stack complements these tools by providing a robust log management solution with advanced features and integration capabilities.

Final thoughts

Fluentd and Fluent Bit emerge as powerful and versatile tools in log forwarding and processing. Fluent Bit stands out for its low memory footprint and high performance, making it particularly suitable for systems with stringent memory requirements. On the other hand, Fluentd, while requiring a bit more memory, excels with its extensive community of plugins, offering robust solutions for diverse log processing needs.

Choosing the right tool depends on your requirements and the platforms you intend to run them on. If memory constraints are a primary consideration, Fluent Bit is an excellent choice for such environments. However, Fluentd, with its rich plugin ecosystem, becomes a compelling option for scenarios demanding extensive log processing capabilities.

Ultimately, before making a final decision, it's advisable to benchmark both tools against your specific use case. Consider the trade-offs between memory usage, performance, and the features offered by each tool.

Thanks for reading, and happy logging!

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