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How to Collect Logs with Fluentd?

How to Collect Logs with Fluentd

Logs are an essential part of any software application, providing valuable insight into how the system is running and any errors that may be occurring. Collecting logs can be a complex task, particularly in a distributed environment with multiple services and applications. Fluentd is an open-source data collector that can help simplify the process of collecting and forwarding logs from different sources. In this article, we will provide a step-by-step guide on how to collect logs with Fluentd.


  • A server or virtual machine with Fluentd installed
  • Access to the log files or sources that you want to collect logs from

Step 1: Install Fluentd

The first step is to install Fluentd on the server or virtual machine that will be responsible for collecting logs. Fluentd can be installed on various operating systems, including Linux, macOS, and Windows. The installation instructions will vary depending on the operating system you are using, but you can find detailed installation instructions on the Fluentd website.

Step 2: Configure Fluentd

Once Fluentd is installed, the next step is to configure it to collect logs. Fluentd uses configuration files to determine which logs to collect and where to send them. The configuration files are written in a simple syntax, making it easy to customize the configuration to your needs. The configuration files are typically located in the /etc/fluentd/ directory.

Here is an example configuration file that collects logs from a file and forwards them to Elasticsearch:

@type tail
path /var/log/messages
pos_file /var/log/td-agent/messages.pos
tag system
format syslog

<match system>
@type elasticsearch
hosts localhost:9200
index_name system-%Y.%m.%d

This configuration file collects logs from the /var/log/messages file, applies the syslog format to them, and forwards them to Elasticsearch. The logs are tagged with the system tag, and the index name in Elasticsearch is based on the date.

Step 3: Start Fluentd

Once Fluentd is configured, the next step is to start the Fluentd service. On Linux, you can start the service using the following command:

sudo service td-agent start

This command will start the Fluentd service and begin collecting logs based on the configuration file.

Step 4: Verify Logs are Collected

To verify that Fluentd is collecting logs correctly, you can check the Fluentd logs or view the logs in the destination that you specified in the configuration file. For example, if you are forwarding logs to Elasticsearch, you can view the logs using the Kibana interface.

Step 5: Additional Configuration Options

Fluentd provides many configuration options that allow you to customize the way logs are collected and forwarded. Here are a few examples:

  • Input plugins: Fluentd supports various input plugins, such as tail, syslog, and TCP. Each input plugin has its configuration options that you can use to customize how the logs are collected.
  • Output plugins: Fluentd supports various output plugins, such as Elasticsearch, MongoDB, and AWS S3. Each output plugin has its configuration options that you can use to customize how the logs are forwarded.
  • Filters: Fluentd supports filters that allow you to modify or parse log data before it is sent to the output destination.

With this guide, you should now have a basic understanding of how to collect logs with Fluentd. Fluentd is a powerful tool that can simplify the process of collecting logs in a distributed environment, and with its many configuration options, you can customize it to meet your specific needs.

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  • That's it for this post. Keep practicing and have fun. Leave your comments if any.

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