Free Alternative To Splunk

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 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 24.04. If you're not familiar with Fluentd, please learn more about Fluentd first.

Prerequisites

• Java runtime (OpenJDK - JRE 21)

• Fluentd

• Elasticsearch

• Kibana

• Fluentd Elasticsearch Plugin

You can install Fluentd via major packaging systems.

• Installation

Java for Elasticsearch

Please confirm that Java version 21 or higher is installed:

$ java --version
openjdk 21.0.5 2024-10-15
OpenJDK Runtime Environment (build 21.0.5+11-Ubuntu-1ubuntu124.04)
OpenJDK 64-Bit Server VM (build 21.0.5+11-Ubuntu-1ubuntu124.04, mixed mode, sharing)

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-8.17.1-linux-x86_64.tar.gz
$ tar -xf elasticsearch-8.17.1-linux-x86_64.tar.gz
$ cd elasticsearch-8.17.1

Once the installation is complete, start Elasticsearch:

$ ./bin/elasticsearch

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.

$ curl -O https://artifacts.elastic.co/downloads/kibana/kibana-8.17.1-linux-x86_64.tar.gz
$ tar -xf kibana-8.17.1-linux-x86_64.tar.gz
$ cd kibana-8.17.1-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 (fluent-package)

You can install Fluentd via major packaging systems.

• Installation

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

See Plugin Management section how to install fluent-plugin-elasticsearch on your environment.

We'll configure fluent-package (Fluentd) to interface properly with Elasticsearch. Please modify /etc/fluent/fluentd.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
  host localhost
  user elastic
  password (ELASTIC_USER_PASSWORD_HERE)
  logstash_format true
  scheme https
  ssl_verify false
  include_timestamp 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 fluentd:

$ sudo systemctl start fluentd

Set Up rsyslogd

The final step is to forward the logs from your rsyslogd to fluentd. Please create the file with following line to /etc/rsyslog.d/90-fluentd.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:

$ 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 patterns 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 fluentd configuration, using filter_stdout will be useful. All the logs including errors can be found at /etc/fluent/fluentd.log.

<filter syslog.**>
  @type stdout
</filter>

<match syslog.**>
  @type elasticsearch
  host localhost
  user elastic
  password (ELASTIC_USER_PASSWORD_HERE)
  logstash_format true
  scheme https
  ssl_verify false
  include_timestamp 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.