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Logging · head to head

Fluentd vs Loki

Fluentd logo

Fluentd

Logging

Open Source Data Collector for Unified Logging

From
Free
Rated
-
Full reviewWebsite
Loki logo

Loki

Logging

Like Prometheus but for Logs

From
Free
Rated
-
Full reviewWebsite

The short version

  • Each has a real cost: Fluentd fluentd needs more than 60 MB of memory at runtime, against roughly 450 KB for Fluent Bit; Loki the Grafana Cloud free tier caps log ingestion at 50 GB a month with 14 day retention
  • They diverge on capability: Fluentd covers Log collection, Loki covers Log aggregation.
  • Prices and features above were last checked on 30 August 2026.

Where they differ

Only the attributes on which Fluentd and Loki actually diverge.

Attributes where Fluentd and Loki differ
AttributeFluentdLoki
Founded20112014

Identical on both: starting price (Free), pricing model (open-source), free tier (Yes), platforms (Web, Api), user rating (Not yet rated), category (Logging).

What each one covers

Drawn from each product's published feature list. An absence here means we hold no record of it - not that the product lacks it.

Only in Fluentd

  • Log collection
  • Data parsing
  • Filtering and buffering
  • Event routing

Only in Loki

  • Log aggregation
  • Label-based indexing
  • Real-time log streaming
  • LogQL query language

Both cover

  • API
  • Webhooks
  • REST
  • Web support
  • Api support

What people use each for

The jobs each tool is most often brought in to do.

Fluentd

  • Unified log collection and routing from many sources to many destinationsnot Loki
  • Parsing and transforming log records before forwardingnot Loki
  • Aggregating logs from containers into Elasticsearch, S3 or a SIEMnot Loki

Loki

  • Aggregating application and infrastructure logs with label based indexingnot Fluentd
  • Querying logs alongside metrics in Grafananot Fluentd

Where each one falls short

Documented limitations, not opinions. Every one is a constraint you would hit in normal use.

Fluentd

  • Fluentd needs more than 60 MB of memory at runtime, against roughly 450 KB for Fluent Bit
  • Fluentd is built as a Ruby gem and depends on other gems, so a Ruby runtime is required
  • Its capability comes from over 1,000 external plugins rather than built in functionality, so each added input or output is a separate dependency
  • The Fluent Bit documentation states that cloud providers have switched from Fluentd to Fluent Bit for performance and compatibility and calls Fluent Bit the next generation solution

Loki

  • The Grafana Cloud free tier caps log ingestion at 50 GB a month with 14 day retention
  • Paid log pricing is split across three separate meters, at $0.050 per GB processed, $0.400 per GB written and $0.100 per GB retained
  • Retaining logs is billed separately from ingesting them, so keeping data costs on an ongoing basis rather than once
  • The Pro plan carries a $19 a month platform fee before any usage charges

Pricing, plan by plan

Fluentd

Free
  • FreeFree
    • Log collection
    • Data parsing
    • Filtering and buffering

Loki

Free
  • FreeFree
    • Log aggregation
    • Label-based indexing
    • Real-time log streaming

Which should you pick?

Choose Fluentd if

  • You need log collection.
  • You want to start without paying.
  • You work on Web, Api.
  • You also want data parsing.
Fluentd review

Choose Loki if

  • You need log aggregation.
  • You want to start without paying.
  • You work on Web, Api.
  • You also want label-based indexing.
Loki review

Questions people ask

Is Fluentd or Loki better?
Neither clearly leads. Fluentd starts at Free and Loki at Free, and user ratings are close enough to be indistinguishable. Choose on capability and platform support.
Which is cheaper, Fluentd or Loki?
Fluentd starts at Free and Loki at Free.
Does Fluentd or Loki run on more platforms?
Both run on Web, Api, so platform support will not decide this one for you.
Can I use Fluentd for free?
Both have a free tier, so you can try either at no cost before committing.
What is Fluentd best used for?
Fluentd is most often used for unified log collection and routing from many sources to many destinations, parsing and transforming log records before forwarding, aggregating logs from containers into elasticsearch, s3 or a siem. Of those, unified log collection and routing from many sources to many destinations and parsing and transforming log records before forwarding are not what Loki is typically brought in for.
What can Fluentd do that Loki cannot?
Fluentd covers Log collection, Data parsing, Filtering and buffering, Event routing. Loki covers Log aggregation, Label-based indexing, Real-time log streaming, LogQL query language. Both handle API, Webhooks, REST, Web support.

Answered from the vendors’ own pages

Fluentd: How much does Fluentd cost?

Fluentd is free and open-source under the Apache 2 License from the Cloud Native Computing Foundation (CNCF). There are no subscription fees, licensing costs, or commercial pricing tiers.

Source
Loki: What does it cost to use Grafana Loki?

Loki is open source and free under the AGPLv3 license for self-hosted deployments. Grafana's managed Cloud Logs service includes a free tier up to 50GB of logs at no cost.

Source
Loki: Are there paid options for Loki beyond the free tier?

Yes. Grafana Cloud Logs offers paid tiers for teams and enterprises, and Enterprise Logs provides self-managed options with expert support for organizations with data localization or privacy requirements.

Source
Loki: What license does open source Loki use?

Loki is released under the AGPLv3 license, which requires you to share modifications and publish your source code if you deploy modifications publicly.

Source
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