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Software · head to head

Loki vs Fluentd

Loki logo

Loki

Software

Like Prometheus but for Logs

From
Free
Rated
-
Full reviewWebsite
Fluentd logo

Fluentd

Software

Open Source Data Collector for Unified Logging

From
Free
Rated
-
Full reviewWebsite

The short version

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

Where they differ

Only the attributes on which Loki and Fluentd actually diverge.

Attributes where Loki and Fluentd differ
AttributeLokiFluentd
Founded20142011

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

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 Loki

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

Only in Fluentd

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

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.

Loki

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

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

Where each one falls short

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

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

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

Pricing, plan by plan

Loki

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

Fluentd

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

Which should you pick?

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

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

Questions people ask

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