Logstash overview in Elasticsearch

Introduction

Logstash helps collect and organize data from many places so you can understand it better. It makes messy data neat and ready to use.

You want to gather logs from different servers into one place.

You need to change or clean data before saving it.

You want to send data to Elasticsearch for searching.

You want to combine data from many sources into one stream.

You want to monitor your systems by analyzing collected data.

Syntax

Elasticsearch

input {
  plugin_name {
    # plugin settings
  }
}

filter {
  plugin_name {
    # plugin settings
  }
}

output {
  plugin_name {
    # plugin settings
  }
}

Logstash uses three main parts: input to get data, filter to change data, and output to send data.

Each part uses plugins that do specific jobs like reading files or sending data to Elasticsearch.

Examples

This example reads a system log file and prints the data to the screen in a readable format.

Elasticsearch

input {
  file {
    path => "/var/log/syslog"
    start_position => "beginning"
  }
}

output {
  stdout {
    codec => rubydebug
  }
}

This example gets data from Beats, parses Apache logs, and sends the data to Elasticsearch.

Elasticsearch

input {
  beats {
    port => 5044
  }
}

filter {
  grok {
    match => { "message" => "%{COMMONAPACHELOG}" }
  }
}

output {
  elasticsearch {
    hosts => ["localhost:9200"]
  }
}

Sample Program

This simple Logstash config reads input from the keyboard, adds a greeting field, and prints the result.

Elasticsearch

input {
  stdin {}
}

filter {
  mutate {
    add_field => { "greeting" => "Hello, Logstash!" }
  }
}

output {
  stdout {
    codec => rubydebug
  }
}

Important Notes

Logstash runs as a service and reads its configuration from files.

Filters can change, add, or remove data fields to make data useful.

Outputs send data to many places like files, Elasticsearch, or other systems.

Summary

Logstash collects data from many sources and prepares it for analysis.

It uses input, filter, and output sections to organize data flow.

It is useful for monitoring, searching, and understanding data from systems.

Practice

1. What is the primary role of Logstash in the Elastic Stack?

easy

A. To store data in a database

B. To visualize data with dashboards

C. To collect, process, and forward data from various sources

D. To secure the Elastic Stack with authentication

Solution

1. Step 1: Understand Logstash's function

   Logstash is designed to collect and process data from many sources before sending it to storage or analysis tools.

2. Step 2: Compare with other Elastic Stack components

   Elasticsearch stores data, Kibana visualizes it, and security features handle authentication, so these are not Logstash's main roles.

3. Final Answer:

   To collect, process, and forward data from various sources -> Option C

4. Quick Check:

   Logstash = Data collection and processing [OK]

Hint: Remember: Logstash handles data input and processing [OK]

Common Mistakes:

• Confusing Logstash with Elasticsearch or Kibana
• Thinking Logstash stores data permanently
• Assuming Logstash manages security

2. Which section in a Logstash configuration file defines where data comes from?

easy

A. filter

B. input

C. output

D. codec

Solution

1. Step 1: Identify configuration sections

   Logstash config files have three main sections: input, filter, and output.

2. Step 2: Match section to purpose

   The input section specifies data sources, filter modifies data, and output sends data elsewhere.

3. Final Answer:

   input -> Option B

4. Quick Check:

   Data source = input section [OK]

Hint: Input section = data source definition [OK]

Common Mistakes:

• Choosing filter or output instead of input
• Confusing codec with input
• Thinking output defines data source

3. Given this Logstash config snippet:

input { stdin { } } filter { mutate { add_field => { "new_field" => "value" } } } output { stdout { codec => rubydebug } }

What will happen when you type 'hello' and press enter?

medium

A. The input 'hello' is printed with an added field 'new_field' set to 'value'

B. The input 'hello' is discarded and nothing is printed

C. An error occurs because 'add_field' is not valid here

D. The input 'hello' is printed without any changes

Solution

1. Step 1: Analyze input and filter

   The input reads from standard input (stdin). The filter adds a new field named 'new_field' with value 'value' to each event.

2. Step 2: Analyze output

   The output prints the event to stdout using rubydebug codec, which shows all fields including added ones.

3. Final Answer:

   The input 'hello' is printed with an added field 'new_field' set to 'value' -> Option A

4. Quick Check:

   Filter adds field, output shows it [OK]

Hint: Filter adds fields; output shows full event [OK]

Common Mistakes:

• Thinking input is discarded
• Believing add_field causes error
• Assuming output prints raw input only

4. Identify the error in this Logstash config snippet:

input { file { path => "/var/log/syslog" } } filter { grok { match => { "message" => "%{SYSLOGTIMESTAMP:timestamp}" } } } output { elasticsearch { hosts => ["localhost:9200"] } }

medium

A. Elasticsearch output hosts must be a string, not an array

B. Missing closing brace in filter section

C. Grok pattern syntax is incorrect

D. File input path should be an array, not a string

Solution

1. Step 1: Check file input syntax

   The 'path' option for file input expects an array of strings, not a single string.

2. Step 2: Verify other sections

   Filter grok syntax and output hosts as array are correct according to Logstash documentation.

3. Final Answer:

   File input path should be an array, not a string -> Option D

4. Quick Check:

   File path = array required [OK]

Hint: File input path must be an array even for one file [OK]

Common Mistakes:

• Using string instead of array for file path
• Misreading grok pattern syntax
• Thinking output hosts must be string

5. You want to collect logs from multiple servers, add a tag with the server name, and send all logs to Elasticsearch. Which Logstash configuration approach is best?

hard

A. Use multiple input sections with file paths and add tags in filter section, then output to Elasticsearch

B. Use one input section with a wildcard path and add tags in output section

C. Use multiple output sections for each server and add tags in input section

D. Use filter section only to read files and add tags, then output to Elasticsearch

Solution

1. Step 1: Understand data collection from multiple servers

   Multiple input sections allow specifying different file paths per server.

2. Step 2: Add tags in filter section

   The filter section is the right place to add tags like server names to enrich data.

3. Step 3: Output all processed logs to Elasticsearch

   The output section sends all enriched logs to Elasticsearch for indexing.

4. Final Answer:

   Use multiple input sections with file paths and add tags in filter section, then output to Elasticsearch -> Option A

5. Quick Check:

   Input for sources + filter for tags + output to ES [OK]

Hint: Input for sources, filter for tags, output to Elasticsearch [OK]

Common Mistakes:

• Adding tags in output section
• Using filter to read files (wrong place)
• Multiple outputs instead of inputs for servers