​Splunk is a great tool for searching logs, but its high cost makes it prohibitive for many teams. In this article, we present a free and open-source alternative to Splunk by combining three open source projects: Elasticsearch, Kibana, and Fluentd.

​Elasticsearch is an open-source search engine well-known for its ease of use. Kibana is an open-source Web UI that makes Elasticsearch user friendly for marketers, engineers and data scientists alike.

By combining these three tools (Fluentd + Elasticsearch + Kibana) we get a scalable, flexible, easy to use the log search engine with a great Web UI that provides an open-source Splunk alternative, all for free.

In this guide, we will go over the installation, setup, and basic use of this combined log search solution. This article was tested on Ubuntu 16.04 and CentOS 7.4. If you're not familiar with Fluentd, please learn more about Fluentd first.

Prerequisites

Java for Elasticsearch

Please confirm that Java version 8 or higher is installed:

$ java -version
openjdk version "1.8.0_151"
OpenJDK Runtime Environment (build 1.8.0_151-b12)
OpenJDK 64-Bit Server VM (build 25.151-b12, mixed mode)

Set Up Elasticsearch

To install Elasticsearch, please download and extract the Elasticsearch package as shown below:

$ curl -O https://artifacts.elastic.co/downloads/elasticsearch/elasticsearch-6.1.0.tar.gz
$ tar -xf elasticsearch-6.1.0.tar.gz
$ cd elasticsearch-6.1.0

Once the installation is complete, start Elasticsearch:

$ ./bin/elasticsearch

Note: You can also install Elasticsearch (and Kibana) using RPM/DEB packages. For details, please refer to the official instructions.

Set Up Kibana

To install Kibana, download it from the official website and extract it. Kibana is an HTML/CSS/JavaScript application (download). Use the binary for 64-bit Linux systems. For this article, we download the binary for macOS.

$ curl -O https://artifacts.elastic.co/downloads/kibana/kibana-6.1.0-linux-x86_64.tar.gz
$ tar -xf kibana-6.1.0-linux-x86_64.tar.gz
$ cd kibana-6.1.0-linux-x86_64

Once the installation is complete, start Kibana i.e. ./bin/kibana. You can modify its configuration file (config/kibana.yml).

$ ./bin/kibana

Access http://localhost:5601 in your browser.

Set Up Fluentd (td-agent)

In this section, we'll install td-agent, the stable release of Fluentd. Please refer to the guides below for detailed instructions:

• ​Debian Package​

• ​RPM Package​

• ​Ruby gem​

Next, we'll install the Elasticsearch plugin for Fluentd: fluent-plugin-elasticsearch. Then, install fluent-plugin-elasticsearch as follows:

$ sudo /usr/sbin/td-agent-gem install fluent-plugin-elasticsearch --no-document

We'll configure td-agent (Fluentd) to interface properly with Elasticsearch. Please modify /etc/td-agent/td-agent.conf as shown below:

# get logs from syslog
<source>
  @type syslog
  port 42185
  tag syslog
</source>
​
# get logs from fluent-logger, fluent-cat or other fluentd instances
<source>
  @type forward
</source>
​
<match syslog.**>
  @type elasticsearch
  logstash_format true
  <buffer>
    flush_interval 10s # for testing
  </buffer>
</match>

fluent-plugin-elasticsearch comes with a logstash_format option that allows Kibana to search through the stored event logs in Elasticsearch.

Once everything has been set up and configured, start td-agent:

# init
$ sudo /etc/init.d/td-agent start
# or systemd
$ sudo systemctl start td-agent.service

Set Up rsyslogd

The final step is to forward the logs from your rsyslogd to fluentd. Please add the following line to /etc/rsyslog.conf, and restart rsyslog. This will forward the local syslogs to Fluentd, and Fluentd in turn will forward the logs to Elasticsearch.

*.* @127.0.0.1:42185

Please restart the rsyslog service once the modification is complete:

# init
$ sudo /etc/init.d/rsyslog restart
# or systemd
$ sudo systemctl restart rsyslog

Store and Search Event Logs

Once Fluentd receives some event logs from rsyslog and has flushed them to Elasticsearch, you can view, search and visualize the log data using Kibana.

For starters, let's access http://localhost:5601 and click the Set up index patters button in the upper-right corner of the screen.

Kibana will start a wizard that guides you through configuring the data sets to visualize. If you want a quick start, use logstash-* as the index pattern, and select @timestamp as the time-filter field.

After setting up an index pattern, you can view the system logs as they flow in:

For more detail on how to use Kibana, please read the official manual.

To manually send logs to Elasticsearch, please use the logger command:

$ logger -t test foobar

When debugging your td-agent configuration, using filter_stdout will be useful. All the logs including errors can be found at /etc/td-agent/td-agent.log.

<filter syslog.**>
  @type stdout
</filter>
​
<match syslog.**>
  @type elasticsearch
  logstash_format true
  <buffer>
    flush_interval 10s # for testing
  </buffer>
</match>

Conclusion

This article introduced the combination of Fluentd and Kibana (with Elasticsearch) which achieves a free alternative to Splunk: storing and searching machine logs. The examples provided in this article have not been tuned.

If you will be using these components in production, you may want to modify some of the configurations (e.g. JVM, Elasticsearch, Fluentd buffer, etc.) according to your needs.

Learn More

• ​Fluentd Architecture​

• ​Fluentd Get Started​

• ​Downloading Fluentd​

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.