Logstash - Supported Outputs | Adglob Infosystem Pvt Ltd

In this guide we will learn about Supported Outputs in Logstash. Logstash provides multiple Plugins to support various data stores or search engines. The output events of logs can be sent to an output file, standard output or a search engine like Elasticsearch. There are three types of supported outputs in Logstash, which are −

Standard Output
File Output
Null Output

Let us now discuss each of these in detail.

Standard Output (stdout)

It is used for generating the filtered log events as a data stream to the command line interface. Here is an example of generating the total duration of a database transaction to stdout.

logstash.conf

This config file contains a stdout output plugin to write the total sql_duration to a standard output.

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 {
   if [logger] == "TRANSACTION_END" {
      stdout {
         codec => line{format => "%{sql_duration}"}
      }
   }
}

Note − Please install the aggregate filter, if not installed already.

>logstash-plugin install Logstash-filter-aggregate

Run Logstash

We can run Logstash by using the following command.

>logstash –f logsatsh.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

stdout (it will be command prompt in windows or terminal in UNIX)

This is the total sql_duration 320 + 200 = 520.

File Output

Logstash can also store the filter log events to an output file. We will use the above-mentioned example and store the output in a file instead of STDOUT.

logstash.conf

This Logstash config file direct Logstash to store the total sql_duration to an output log file.

input {
   file {
      path => "C:/tpwork/logstash/bin/log/input1.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 {
   if [logger] == "TRANSACTION_END" {
      file {
         path => "C:/tpwork/logstash/bin/log/output.log"
         codec => line{format => "%{sql_duration}"}
      }
   }
}

Run logstash

We can run Logstash by using the following command.

>logstash –f logsatsh.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

The following code block shows the output log data.

Null Output

This is a special output plugin, which is used for analyzing the performance of input and filter Plugins.

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