This article explains how to set up Fluentd with Graylog. Graylog is a popular log management server powered by Elasticsearch and MongoDB. You can combine Fluentd and Graylog to create a scalable log analytics pipeline.

Prerequisites

• Basic Understanding of Fluentd

• Linux Server (Ubuntu 18.04 LTS was used for this guide.)

How to Setup Graylog + Fluentd

Dependencies

Install the dependencies with the following command:

$ sudo apt install mongodb-server openjdk-8-jre-headless uuid-runtime

Elasticsearch

Graylog requires Elasticsearch, which can be instantly launched using the following commands:

# Note that Graylog 2.4 doesn't support Elasticsearch 6.X.
$ wget https://artifacts.elastic.co/downloads/elasticsearch/elasticsearch-5.6.13.tar.gz
$ tar -xzf elasticsearch-5.6.13.tar.gz
$ cd elasticsearch-5.6.13

Elasticsearch is ready. Start it with:

$ ./bin/elasticsearch

Graylog

In this article, we will use Graylog 2.4.

$ wget https://packages.graylog2.org/repo/packages/graylog-2.4-repository_latest.deb
$ sudo dpkg -i graylog-2.4-repository_latest.deb

Update the package cache and install graylog-server:

$ sudo apt update
$ sudo apt install graylog-server

Open /etc/graylog/server/server.conf and configure the following parameters:

1. password_secret

2. root_password_sha2.

3. web_enable

For root_password_sha2, run echo -n ROOT_PASSWORD | sha256sum and set the hash. Also you need to set web_enable to true to access the web interface.

Now let's start Graylog:

$ sudo systemctl start graylog-server

Prepare Graylog for Fluentd

Go to http://localhost:9000 and log into the web interface.

To log in, use admin as the username and YOUR_PASSWORD as the password (the one you have set up for root_password_sha2).

Once logged in, click on System in the top nav. Next, click on Inputs from the left navigation bar. (Or, simply go to http://localhost:9000/system/inputs.

Then, from the dropdown, choose GELF UDP and click on Launch new input, which should pop up a modal dialogue, Select the Node and fill the Title. Then, click Save.

Now, Graylog2 is ready to accept messages from Fluentd over UDP. It's time to configure Fluentd.

Fluentd

See the download page for all the options. Here, we are using the deb package:

$ wget http://packages.treasuredata.com.s3.amazonaws.com/3/ubuntu/bionic/pool/contrib/t/td-agent/td-agent_3.2.1-0_amd64.deb
$ sudo dpkg -i td-agent_3.2.1-0_amd64.deb

Then, install the out_gelf plugin to send data to Graylog. Currently, the GELF plugin is not available on RubyGems, so we need to download the plugin file and place it in /etc/td-agent/plugin:

$ wget https://raw.githubusercontent.com/emsearcy/fluent-plugin-gelf/master/lib/fluent/plugin/out_gelf.rb
$ sudo mv out_gelf.rb /etc/td-agent/plugin

We also need to gem-install GELF's Ruby client:

$ sudo /usr/sbin/td-agent-gem install gelf

Configure /etc/td-agent/td-agent.conf as follows:

<source>
  @type syslog
  tag graylog2
</source>
​
<match graylog2.**>
  @type gelf
  host 0.0.0.0
  port 12201
  <buffer>
    flush_interval 5s
  </buffer>
</match>

Open /etc/rsyslog.conf and add the following line to the file:

*.* @127.0.0.1:5140

Finally, restart rsyslog and Fluentd with the following commands:

$ sudo systemctl restart rsyslog
$ sudo systemctl restart td-agent

Visualize the Data Stream

When you log back into Graylog, you should be seeing a graph like this (wait for events to flow in):

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.