Cleaning up messy distributed logs, part 1

Logging is an important part of software lifecycle. It is used in every stage, from the beginning, through testing, deployment, staging, production. I find neat logs soothing, they increase my confidence in running software providing visibility when required.

Having said that I have taken a task to work on logs in a distributed system I’m working on. Since we push everything through ELK stack this is what I have inherited.

Unfiltered messy kibana logs

It looks like a mess, but this is because kibana does not have any sensible default configuration in our setup. After looking more closely there is another issue. I have marked it with red.

Unfiltered messy kibana logs with tags marked with red

So time to look at how logstash is configured as there is a problem with how grok filter is set up. Before doing that it is worth explaining how can you configure logstash as it will help in understanding my configuration, and maybe explain briefly what logstash is.

Easiest way to describe purpose of this tool is by citing introduction taken from the documentation.

Logstash is an open source data collection engine with real-time pipelining capabilities. Logstash can dynamically unify data from disparate sources and normalize the data into destinations of your choice.

How do you configure it? Simply, by taking the plugins you wish and putting them into your configuration file. Plugins are:

  • input plugins, they are sources of events fed to logstash. list
  • filter plugins, used for processing of event data. list
  • output plugins, send data to particular destination. list
  • codec plugins, can be part of input or output plugins and can change the data. list

In my case configuration is a bit complex and what’s most important grok is not configured correctly (So it seems but there might be something else as well in play). Some of the plugins may be redundant as well but this is not my concern now.

      input {
        gelf { }
        heartbeat { }
        syslog {
          port => 5145
      filter {
        ruby {
          code => "
            event.to_hash.keys.each { |k| event[ k.gsub('"'.'"','"'_'"') ] = 
            event.remove(k) if k.include?'"'.'"' }
        grok {
          match => {
            "message" => [
              # Logspout
              "%{SYSLOG5424PRI}%{NONNEGINT:ver} +(?:%{TIMESTAMP_ISO8601:ts}|-) 
              +(?:%{NOTSPACE:proc}|-) +(?:%{WORD:msgid}|-) 
              +(?:%{SYSLOG5424SD:sd}|-|) +%{GREEDYDATA:msg}"
      output {
        elasticsearch {
          hosts => ["elasticsearch:9200"]
        stdout {
          codec => rubydebug

This is the state now, further on I’ll describe as I go, my quest to make logs great again.

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