What is the difference between Fluentd and Logstash?

Logstash is an open-source server data processing pipeline that dynamically ingests data from multiple sources, transforms it, and sends it to selected destinations. It is part of the ELK stack (Elasticsearch, Logstash, Kibana).

Fluentd is an open-source data collector for unified logging. It has a modular structure and is more lightweight compared to Logstash, making it suitable for microservices architectures and deployment on edge nodes.

Main differences:

Criterion	Fluentd	Logstash
Architecture	Proprietary, lightweight	JVM-based, resource-intensive
Performance	High, low resource consumption	Can be high with large data volumes
Plugins	Over 1000 available plugins	Less than 200 available plugins
Plugin language	Ruby, C	Ruby
Flexibility	High, modular	Less flexible
Parsing	Uses Ruby DSL	Uses Grok
Operating system	Linux, macOS, Windows	Linux, macOS, Windows

Example Fluentd configuration for log collection and sending to Elasticsearch:

# source plugin to collect logs from a file
<source>
  @type tail
  path /var/log/myapp/access.log
  pos_file /var/log/td-agent/pos/access.log.pos
  tag myapp.access
  format apache
</source>

# match plugin to send logs to Elasticsearch
<match myapp.access>
  @type elasticsearch
  host elasticsearch.example.com
  port 9200
  logstash_format true
  logstash_prefix myapp
  index_name myapp_logs
  type_name myapp_type
</match>

Example Logstash configuration for log collection and sending to Elasticsearch:

# input plugin to collect logs from a file
input {
  file {
    path => "/var/log/myapp/access.log"
    start_position => "beginning"
  }
}

# filter plugin to parse log data
filter {
  grok {
    match => { "message" => "%{COMBINEDAPACHELOG}" }
  }
}

# output plugin to send logs to Elasticsearch
output {
  elasticsearch {
    hosts => ["elasticsearch.example.com:9200"]
    index => "myapp-logs-%{+YYYY.MM.dd}"
  }
}