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Send Apache Logs to S3

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

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 three (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 a one-node configuration. Please install the following software on the same node:

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

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
  path /var/log/apache2/access_log
  pos_file /var/log/td-agent/apache2.access_log.pos
  <parse>
    @type apache2
  </parse>
  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. @type apache2 in <parse>: 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>
    @type file
    path /var/log/td-agent/s3
    timekey 3600  # 1 hour
    timekey_wait 10m
    chunk_limit_size 256m
  </buffer>

  time_slice_format %Y%m%d%H
</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 timekey condition has been met. To change the output frequency, please modify the timekey value. To write objects every minute, please use timekey 60 with smaller timekey_wait like timekey_wait 10s.

Conclusion

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

Learn More

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.