Logstash - Filters

Logstash uses filters in the middle of the pipeline between input and output. The filters of Logstash measures manipulate and create events like Apache-Access. Many filter plugins used to manage the events in Logstash. Here, in an example of the Logstash Aggregate Filter, we are filtering the duration every SQL transaction in a database and computing the total time.

Installing the Aggregate Filter Plugin

Installing the Aggregate Filter Plugin using the Logstash-plugin utility. The Logstash-plugin is a batch file for windows in bin folder in Logstash.

>logstash-plugin install logstash-filter-aggregate

logstash.conf

In this configuration, you can see three ‘if’ statements for Initializing, Incrementing, and generating the total duration of transaction, i.e., the sql_duration. The aggregate plugin is used to add the sql_duration, present in every event of the input log.

input {
   file {
      path => "C:/tpwork/logstash/bin/log/input.log"
   }
} 
filter {
   grok {
      match => [
         "message", "%{LOGLEVEL:loglevel} - 
            %{NOTSPACE:taskid} - %{NOTSPACE:logger} - 
            %{WORD:label}( - %{INT:duration:int})?" 
      ]
   }
   if [logger] == "TRANSACTION_START" {
      aggregate {
         task_id => "%{taskid}"
         code => "map['sql_duration'] = 0"
         map_action => "create"
      }
   }
   if [logger] == "SQL" {
      aggregate {
         task_id => "%{taskid}"
         code => "map['sql_duration'] ||= 0 ;
            map['sql_duration'] += event.get('duration')"
      }
   }
   if [logger] == "TRANSACTION_END" {
      aggregate {
         task_id => "%{taskid}"
         code => "event.set('sql_duration', map['sql_duration'])"
         end_of_task => true
         timeout => 120
      }
   }
}
output {
   file {
      path => "C:/tpwork/logstash/bin/log/output.log"    
   }
}

Run Logstash

We can run Logstash by using the following command.

>logstash –f logstash.conf 

input.log

The following code block shows the input log data.

INFO - 48566 - TRANSACTION_START - start
INFO - 48566 - SQL - transaction1 - 320
INFO - 48566 - SQL - transaction1 - 200
INFO - 48566 - TRANSACTION_END - end

output.log

As specified in the configuration file, the last ‘if’ statement where the logger is – TRANSACTION_END, which prints the total transaction time or sql_duration. This has been highlighted in yellow color in the output.log.

{
   "path":"C:/tpwork/logstash/bin/log/input.log","@timestamp": "2016-12-22T19:04:37.214Z",
   "loglevel":"INFO","logger":"TRANSACTION_START","@version": "1","host":"wcnlab-PC",
   "message":"8566 - TRANSACTION_START - start\r","tags":[]
}
{
   "duration":320,"path":"C:/tpwork/logstash/bin/log/input.log",
   "@timestamp":"2016-12-22T19:04:38.366Z","loglevel":"INFO","logger":"SQL",
   "@version":"1","host":"wcnlab-PC","label":"transaction1",
   "message":" INFO - 48566 - SQL - transaction1 - 320\r","taskid":"48566","tags":[]
}
{
   "duration":200,"path":"C:/tpwork/logstash/bin/log/input.log",
   "@timestamp":"2016-12-22T19:04:38.373Z","loglevel":"INFO","logger":"SQL",
   "@version":"1","host":"wcnlab-PC","label":"transaction1",
   "message":" INFO - 48566 - SQL - transaction1 - 200\r","taskid":"48566","tags":[]
}
{
   "sql_duration":520,"path":"C:/tpwork/logstash/bin/log/input.log",
   "@timestamp":"2016-12-22T19:04:38.380Z","loglevel":"INFO","logger":"TRANSACTION_END",
   "@version":"1","host":"wcnlab-PC","label":"end",
   "message":" INFO - 48566 - TRANSACTION_END - end\r","taskid":"48566","tags":[]
}