This article discusses the post-installation steps for the new Fluentd users assuming that Fluentd has been installed using the td-agent package.

System Administration

Configuration File

After the successful installation, a td-agent instance will be up and running with a predefined template configuration file.

The default path for this configuration file is:

/etc/td-agent/td-agent.conf

You may edit this configuration file according to your own use case.

After editing the configuration file, restart td-agent using systemctl command:

$ sudo systemctl restart td-agent

Logging

By default, td-agent writes its operation logs to the following file:

/var/log/td-agent/td-agent.log

For more verbose logs, read the article on Troubleshooting.

Connect to the Other Services

How It Works

In Fluentd, the most important part of data input/output is managed by plugins. Each plugin knows how to interface with an external endpoint and is solely responsible for managing one pipeline to forward data streams.

Plugins use a certain naming convention. For example, if it receives data and interfaces with Apache Kafka, it is called in_kafka. In the same way, if it publishes data and connects to MongoDB, it is called out_mongo.

The following configuration uses the in_forward plugin as an input source and out_file plugin as an output endpoint:

<source>
  @type forward
  port 9999
</source>
<match app.**>
  @type file
  path /var/log/app/data.log
  compress gzip
</match>

Plugin Management

Fluentd manages plugins as Ruby gems but stores them in their dedicated directory separated from the normal Ruby gems.

A special program td-agent-gem is used to manage plugin gems. For example, the following command installs a plugin to connect to S3 (including both in_s3 and out_s3 plugins):

 $ sudo /usr/sbin/td-agent-gem install fluent-plugin-s3

Available Plugins

See the List Of All Plugins to explore the available third-party plugins.

Note that a number of plugins are bundled with the standard distribution of td-agent so you do not need to install them manually.

Configuration Syntax

Data Source

A configuration file consists of a number of setting blocks or sections e.g. <source>. Each block contains a set of options for a specific data endpoint.

For example, if you want to create an endpoint to receive data from syslog, you need to add a <source> block and set up its settings like this:

<source>
  @type syslog
  port 5140
  tag system
</source>

The @type parameter specifies which plugin to use. Note that the plugin type prefix i.e. in_, out_, etc. is not needed here. In this example, the input plugin is specified as syslog, not in_syslog.

Output Endpoint

To add an output endpoint for the data stream, you need to define a <match> block. Syntactically, <match> is slightly different from <source> in the sense that it requires a filter expression as an argument.

For example, if you want to output events tagged with debug.log, you need to mention this tag as an argument in <match> like this:

<match debug.log>
  @type kafka2
  port 5140
  brokers kafka-server:9092
  tag system
  # ...
</match>

The wildcard character * can be used in the filter expression. For example, debug.* matches debug.log, debug.foo, etc.

To catch all the descendent tags, use double asterisks **. For example, debug.** matches not only debug.log, but also debug.log.bar or debug.log.level.critical, etc.

Further Reading

• ​Configuration File Syntax​

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 2 License.