Which version of Ruby does fluentd support?

Latest fluentd works on Ruby 2.5 or later.

Though the minimum required version is Ruby 2.5 or later, we recommend using fluentd with more newer stable version.

What is the difference between v1 or v0.14?

No difference. v1 is built on top of v0.14. Use v1 for a newer installation. We use v1 or v1.x on our document.


I have a weird timestamp value, what happened?

The timestamps of Fluentd and its logger libraries depend on your system's clock. It is highly recommended that you set up NTP on your nodes so that your clocks remain synced with the correct clocks.

I installed td-agent/fluent-package and want to add custom plugins. How do I do it?

Use the bundled gem system. See this section for more information.

How can I match (send) an event to multiple outputs?

You can use the copy output plugin to send the same event to multiple output destinations.

How can I use environment variables to configure parameters dynamically?

Use "#{ENV['YOUR_ENV_VARIABLE']}". For example:

some_field "#{ENV['FOO_HOME']}"

Note that it must be double quotes, not single quotes.

Fluentd raises an error for host:port. Why?

There are several reasons:

  • If you get Address already in use error, another process has already

    used host:port. Check port conflict between processes/plugins.

  • If you get Permission denied error, you likely tried to use a well-known

    port without permission. Search well-known ports for how to use well-known ports.

    Use capabilities or something.

If you get other errors, Google it.

fluentd raises tzinfo conflict error after installed plugins

Fluentd supports tzinfo v1.1 or later and recent td-agent / fluent-package / official images install tzinfo v2 by default. The problem is several plugins depend on ActiveSupport and ActiveSupport doesn't support tzinfo v2. To resolve this problem, there are 2 approaches.

  • Uninstall tzinfo v2 and install tzinfo v1.1 manually

  • Update plugin to remove ActiveSupport dependency. ActiveSupport is mainly for Ruby on Rails,

    so using ActiveSupport for several convenient methods is overengineering.

Former is easier approach.

I got no patterns matched in the log, why?

This means that the event is emitted but there is no <match> directive for it. For example, if you emit the event with foo.bar tag, you need to define <match> for foo.bar tag like <match foo.**>.

See also: Lifecycle of a Fluentd event or Config File

File buffer does not work properly, why?

file buffer has limitations. Check buf_file article.

I got encoding error inside the plugin. How to fix it?

You may hit "\xC3" from ASCII-8BIT to UTF-8 like UndefinedConversionError in the plugin. This error happens when string encoding is set to ASCII-8BIT but the actual content is UTF-8. Fluentd and all its plugins treat the logs as ASCII-8BIT by default but some libraries assume that the log encoding is UTF-8. This is why this error occurs.

There are several approaches to avoid this problem:

  • Set encoding correctly:

  • Use yajl(Yajl.load/Yajl.dump) instead of json when error happens

    inside JSON.parse/JSON.dump/to_json.

Fluentd warns Oj is not installed, and falling back to Yajl for json parser.

If you are using Alpine Linux, you need to install ruby-bigdecimal to use Oj as the JSON parser. Please Execute the following command to see if the warning persists:

# apk add --update ruby-bigdecimal

Plugin Development

How do I develop a custom plugin?

Please refer to the Plugin Development Guide.


How can I parse <my complex text log>?

If you are willing to write Regexp, fluentd-ui's in_tail editor or Fluentular is a great tool to verify your Regexps.

If you do NOT want to write any Regexp, look at the Grok parser.

If this article is incorrect or outdated, or omits critical information, please let us know. Fluentd is an open-source project under Cloud Native Computing Foundation (CNCF). All components are available under the Apache License 2.0.

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