How to use logstash with docker?

[mohhef (Mohamed Hefny)]

Hello,

My enviroment:
Host: windows 10
Containers: linux

I am building a spring boot application and I am logging my logs to "C:/elk/spring-boot-elk.log"
I want to have a docker setup such that logstash will be able to read from that file whenever it is updated. I have no idea how should I proceed with this.

my docker file:

version: "3.3"
services:
  elasticsearch:
    image: docker.elastic.co/elasticsearch/elasticsearch:7.9.3
    container_name: elasticsearch
    environment:
      - discovery.type=single-node
    volumes:
      - elasticsearch-data:/usr/share/elasticsearch/data
    ports:
      - 9200:9200
    networks:
      - elknetwork

  kibana:
    container_name: kibana
    image: docker.elastic.co/kibana/kibana:7.9.3
    environment:
      - ELASTICSEARCH_HOSTS=http://elasticsearch:9200    # address of elasticsearch docker container which kibana will connect
    ports:
      - 5601:5601
    depends_on:
      - elasticsearch                                   # kibana will start when elasticsearch has started
    networks:
      - elknetwork

  logstash:
    image: logstash:7.9.3
    container_name: logstash
    links:
      - elasticsearch:elasticsearch
    volumes:
      - ./:/config-dir
    command: logstash -f /config-dir/logstash.conf
    depends_on:
      - elasticsearch
    networks:
      - elknetwork

networks:
  elknetwork:
    driver: bridge

volumes:
  elasticsearch-data:

my logstash.conf file

input {
  file {
    type => "java"
    path => "C:/elk/spring-boot-elk.log"
    start_position => "beginning"
    codec => multiline {
      pattern => "^%{YEAR}-%{MONTHNUM}-%{MONTHDAY} %{TIME}.*"
      negate => "true"
      what => "previous"
    }
  }
}

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

however when running the docker containers, i get this error:

 [2020-10-29T02:59:02,245][ERROR][logstash.javapipeline    ][main] Pipeline error {:pipeline_id=>"main", :exception=>#<ArgumentError: File paths must be absolute, relative path specified: C:/elk/spring-boot-elk.log>, :backtrace=>["/usr/share/logstash/vendor/bundle/jruby/2.5.0/gems/logstash-input-file-4.2.2/lib/logstash/inputs/file.rb:283:in `block in register'", "org/jruby/RubyArray.java:1809:in `each'", "/usr/share/logstash/vendor/bundle/jruby/2.5.0/gems/logstash-input-file-4.2.2/lib/logstash/inputs/file.rb:281:in `register'", "/usr/share/logstash/logstash-core/lib/logstash/java_pipeline.rb:228:in `block in register_plugins'", "org/jruby/RubyArray.java:1809:in `each'", "/usr/share/logstash/logstash-core/lib/logstash/java_pipeline.rb:227:in `register_plugins'", "/usr/share/logstash/logstash-core/lib/logstash/java_pipeline.rb:386:in `start_inputs'", "/usr/share/logstash/logstash-core/lib/logstash/java_pipeline.rb:311:in `start_workers'", "/usr/share/logstash/logstash-core/lib/logstash/java_pipeline.rb:185:in `run'", "/usr/share/logstash/logstash-core/lib/logstash/java_pipeline.rb:137:in `block in start'"], "pipeline.sources"=>["/config-dir/logstash.conf"], :thread=>"#<Thread:0x4fcfe8a8 run>"}

my guess is that logstash can't read the log file because logstash is running on a docker container and thus it will not be able to see my host file.

[Iker (Iker Saint)]

You are right, you need to map the volume to the container with the specific file or folder; for example:

[mohhef (Mohamed Hefny)]

@mohhef

    depends_on:

Thank you for your reply,
I am a bit new to docker but from my understanding. When you mount a volume, you transfer the files from the host to the docker container. Is that correct?

What if I want to keep logging to my log file on the host and I want docker to also have the updated log files?

[Iker (Iker Saint)]

It doesn't work like that, there are two main ways to use "Volumes"

1. "Volumes": The volume is in your disk as a file, the container see the volume as a folder in an specific path (Mount point), the host can't see the volume contents directly.
2. "Bind Mount": You create a volume that binds directly to a file or folder on the host, the container see the volume as a folder or a file in a specific path (Mount Point), the host can access directly the volume and modify his content, these changes can be seen by the container in real time.

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