This article explains how to use Fluentd's Amazon S3 Output plugin (out_s3) to aggregate semi-structured logs in real-time.

Background

​Fluentd is an advanced open-source log collector originally developed at Treasure Data, Inc. One of the main objectives of log aggregation is data archiving. Amazon S3, the cloud object storage provided by Amazon, is a popular solution for data archiving.

This article will show you how to use Fluentd to import Apache logs into Amazon S3.

Mechanism

Fluentd does 3 things:

1. It continuously "tails" the access log file.

2. It parses the incoming log entries into meaningful fields (such as

   ip, path, etc.) and buffers them.

3. It writes the buffered data to Amazon S3 periodically.

Install

For simplicity, this article will describe how to set up an one-node configuration. Please install the following software on the same node.

• ​Fluentd​

• ​Amazon S3 Output Plugin​

• Your Amazon Web Services Account

• Apache (with the Combined Log Format)

The Amazon S3 Output plugin is included in the latest version of Fluentd's deb/rpm package. If you want to use Ruby Gems to install the plugin, please use gem install fluent-plugin-s3.

• ​Debian Package​

• ​RPM Package​

• ​Ruby gem​

Configuration

Let's start configuring Fluentd. If you used the deb/rpm package, Fluentd's config file is located at /etc/td-agent/td-agent.conf. Otherwise, it is located at /etc/fluentd/fluentd.conf.

Tail Input

For the input source, we will set up Fluentd to track the recent Apache logs (typically found at /var/log/apache2/access_log) The Fluentd configuration file should look like this:

<source>
  @type tail
  format apache2
  path /var/log/apache2/access_log
  pos_file /var/log/td-agent/apache2.access_log.pos
  tag s3.apache.access
</source>

Please make sure that your Apache outputs are in the default \'combined\' format. `format apache2` cannot parse custom log formats. Please see the in_tail article for more information.

Let's go through the configuration line by line.

1. type tail: The tail Input plugin continuously tracks the log file.

   This handy plugin is included in Fluentd's core.

2. format apache2: Uses Fluentd's built-in Apache log parser.

3. path /var/log/apache2/access_log: The location of the Apache log.

   This may be different for your particular system.

4. tag s3.apache.access: s3.apache.access is used as the tag to

   route the messages within Fluentd.

That's it! You should now be able to output a JSON-formatted data stream for Fluentd to process.

Amazon S3 Output

The output destination will be Amazon S3. The output configuration should look like this:

<match s3.*.*>
  @type s3
​
  aws_key_id YOUR_AWS_KEY_ID
  aws_sec_key YOUR_AWS_SECRET/KEY
  s3_bucket YOUR_S3_BUCKET_NAME
  path logs/
  buffer_path /var/log/td-agent/s3
​
  time_slice_format %Y%m%d%H
  time_slice_wait 10m
  utc
​
  buffer_chunk_limit 256m
</match>

The match section specifies the regexp used to look for matching tags. If a matching tag is found in a log, then the config inside <match>...</match> is used (i.e. the log is routed according to the config inside). In this example, the s3.apache.access tag (generated by tail) is always used.

Test

To test the configuration, just ping the Apache server. This example uses the ab (Apache Bench) program.

$ ab -n 100 -c 10 http://localhost/

Then, log into your AWS Console and look at your bucket.

WARNING: By default, files are created on an hourly basis (around xx:10). This means that when you first import records using the plugin, no file is created immediately. The file will be created when the time_slice_format condition has been met. To change the output frequency, please modify the time_slice_format value. To write files every minute, please use %Y%m%d%H%M for the time_slice_format.

Conclusion

Fluentd + Amazon S3 makes real-time log archiving simple.

Learn More

• ​Fluentd Architecture​

• ​Fluentd Get Started​

• ​Amazon S3 Output plugin​

If this article is incorrect or outdated, or omits critical information, please let us know. Fluentd is a open source project under Cloud Native Computing Foundation (CNCF). All components are available under the Apache 2 License.