Aggregating Apache logs with Fluentd and Amazon S3

17 Oct 2014

HackerEarth infrastructure is hosted on Amazon services. At any given point of time many webservers are running concurrently serving thousands of requests. This generates tons of access and error logs on each server separately. The task here was to parse the logs on all these webservers and store them at one place in a format that can further be used to derive meaningful insights from the data. We tried to accomplish this using fluentd and Amazon S3.


Fluentd does the following things:

  1. Continuously tails apache log files.
  2. Parses incoming entries into meaning fields like ip, address etc and buffers them.
  3. Writes the buffered data to Amazon S3 periodically.


The stable version of fluentd is called td-agent and we are using the same for our purpose here. For ubuntu 12.04 LTS the following shell command will install td-agent on your system.

curl -L | sh

The other supported operating systems and installation methods are listed here.

Please note that if you are installing ruby using Ruby Gems, you will have to install Amazon S3 output plugin separately. This can be done by:

gem install fluent-plugin-s3


Once td-agent is installed you will find a td-agent.conf file in /etc/td-agent/ directory. For parsing apache access logs you will need to add the following configuration:

    type tail                           # for continuosly tailing the log
    format apache2                      # for default format of apache access logs
    time_format %d/%b/%Y:%H:%M:%S %z    # time format in access logs
    path /var/log/apache2/access.log    # path from where log is to be read

    # if td-agent restarts, it starts reading from the
    #last position td-agent read before the restart
    pos_file /var/log/td-agent/apache2.access_log.pos

    tag s3.apache.access                # for identifying the log stream uniquely

<match s3.*.*>
    type s3                             # plugin for writing the log to s3
    aws_key_id <YOUR AWS KEY ID>
    aws_sec_key <YOUR AWS SECRET KEY>
    s3_bucket <YOUR S3 BUCKET NAME>
    path <PATH ON BUCKET>

    #place where the stream is stored before being written on s3
    buffer_path /var/log/td-agent/s3/

    # this specifies the interval at which logs are to written to s3.
    # this format specifies daily writes
    time_slice_format %Y%m%d

    # the amount of time fluentd will wait for old logs to arrive

    time_slice_wait 10m

    buffer_chunk_limit 256m            # max size of a buffer chunk

This configuration is for the default apache access.log file and the filter for this is predefined in td-agent(i.e format apache2). If you want to use some other log format you will need to write a regular expression for parsing those logs.

If you are using vhost_combined format for access logs, all you need to do is to replace apache2 in the second line the source block with this:

format /^(?<virtualhost>[^ ]*)[:](?<port>[^ ]*) (?<host>[^]*)"(?<forwardedfor>[^\"]*)" [^ ]* (?<user>[^ ]*)\[(?<time>[^\]]*)\]"(?<method>\S+)(?: +(?<path>[^ ]*) +\S*)?" (?<code>[^ ]*)(?<size>[^ ]*)(?:"(?<referer>[^\"]*)" "(?<agent>[^\"]*)")?$/

Please refer to this article for other pre-available log formats.


To test your configuration run this command in your terminal

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

Now login to your Amazon console and check the generated logs. With the above configuration you should be sucessfully able to write your apache access logs to Amazon S3 on a daily basis.

Further these logs can be used to analyzed using ElasticSearch and LogStash/Kibana to analyze all the requests that your web servers receive.

This blog is mostly a reproduction of the official fluentd blog with a little detailed expanation.

P.S. I am a developer at HackerEarth Reach out to me at for any suggestion, bugs or even if you just want to chat! Follow me @virendra2334

Posted by Virendra Jain

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