Answer a question

I created a Docker volume as such:

sudo docker volume create --driver=local --name=es-data1 --opt type=none --opt o=bind --opt device=/usr/local/contoso/data1/elasticsearch/data1

• /usr/local/contoso/data1/elasticsearch/data1 is a symlink.

And I'm instantiating three Elasticsearch Docker containers in my docker-compose.yml file as such:

version: '3.7'
services:
  elasticsearch:
    image: docker.elastic.co/elasticsearch/elasticsearch:7.6.0
    logging:
      driver: none
    container_name: elasticsearch1
    environment:
      - node.name=elasticsearch1
      - cluster.name=docker-cluster
      - cluster.initial_master_nodes=elasticsearch1
      - bootstrap.memory_lock=true
      - "ES_JAVA_OPTS=-Xms1G -Xmx1G"
      - http.cors.enabled=true
      - http.cors.allow-origin=*
      - network.host=_eth0_          
    ulimits:
      nproc: 65535
      memlock:
        soft: -1
        hard: -1
    cap_add:
      - ALL
    # privileged: true
    deploy:
      replicas: 1
      update_config:
        parallelism: 1
        delay: 10s
      resources:
        limits:
          cpus: '1'
          memory: 1G
        reservations:
          cpus: '1'
          memory: 1G
      restart_policy:
        condition: unless-stopped
        delay: 5s
        max_attempts: 3
        window: 10s
    volumes:
      - es-logs:/var/log
      - es-data1:/usr/share/elasticsearch/data
    networks:
      - elastic
      - ingress
    ports:
      - 9200:9200
      - 9300:9300
    healthcheck:
      test: wget -q -O - http://127.0.0.1:9200/_cat/health
  elasticsearch2:
    image: docker.elastic.co/elasticsearch/elasticsearch:7.6.0
    logging:
      driver: none
    container_name: elasticsearch2
    environment:
      - node.name=elasticsearch2
      - cluster.name=docker-cluster
      - cluster.initial_master_nodes=elasticsearch1
      - bootstrap.memory_lock=true
      - "ES_JAVA_OPTS=-Xms1G -Xmx1G"
      - "discovery.zen.ping.unicast.hosts=elasticsearch1"
      - http.cors.enabled=true
      - http.cors.allow-origin=*
      - network.host=_eth0_          
    ulimits:
      nproc: 65535
      memlock:
        soft: -1
        hard: -1
    cap_add:
      - ALL
    # privileged: true
    deploy:
      replicas: 1
      update_config:
        parallelism: 1
        delay: 10s
      resources:
        limits:
          cpus: '1'
          memory: 1G
        reservations:
          cpus: '1'
          memory: 1G
      restart_policy:
        condition: unless-stopped
        delay: 5s
        max_attempts: 3
        window: 10s
    volumes:
      - es-logs:/var/log
      - es-data2:/usr/share/elasticsearch/data
    networks:
      - elastic
      - ingress
    ports:
      - 9201:9200
    healthcheck:
      test: wget -q -O - http://127.0.0.1:9200/_cat/health
  elasticsearch3:
    image: docker.elastic.co/elasticsearch/elasticsearch:7.6.0
    logging:
      driver: none
    container_name: elasticsearch3
    environment:
      - node.name=elasticsearch3
      - cluster.name=docker-cluster
      - cluster.initial_master_nodes=elasticsearch1
      - bootstrap.memory_lock=true
      - "ES_JAVA_OPTS=-Xms1G -Xmx1G"
      - "discovery.zen.ping.unicast.hosts=elasticsearch1"
      - http.cors.enabled=true
      - http.cors.allow-origin=*
      - network.host=_eth0_          
    ulimits:
      nproc: 65535
      memlock:
        soft: -1
        hard: -1
    cap_add:
      - ALL
    # privileged: true
    deploy:
      replicas: 1
      update_config:
        parallelism: 1
        delay: 10s
      resources:
        limits:
          cpus: '1'
          memory: 1G
        reservations:
          cpus: '1'
          memory: 1G
      restart_policy:
        condition: unless-stopped
        delay: 5s
        max_attempts: 3
        window: 10s
    volumes:
      - es-logs:/var/log
      - es-data3:/usr/share/elasticsearch/data
    networks:
      - elastic
      - ingress
    ports:
      - 9202:9200
    healthcheck:
      test: wget -q -O - http://127.0.0.1:9200/_cat/health
volumes:
  es-data1:
    driver: local
    external: true
  es-data2:
    driver: local
    external: true
  es-data3:
    driver: local
    external: true
  es-logs:
    driver: local
    external: true     
networks:
  elastic:
    external: true
  ingress:
    external: true

My Problem:

• The Elasticsearch containers are persisting index data to both the host filesystem and the mounted symlink.

My Question:

• How do I modify my configuration so that the Elasticsearch containers are only persisting index data to the mounted symlink?

Answers

It seems to be the default behavior of the local volume driver that the files are additionally stored on the host machine. You can change the volume settings in your docker-compose.yml to prevent the docker from persisting (copying) files on the host file system (see nocopy: true), like so:

version: '3.7'
services:
  elasticsearch:
    ....
    volumes:
      - type: volume
        source: es-data1
        target: /usr/share/elasticsearch/data
        volume:
          nocopy: true
    ....
volumes:
  es-data1:
    driver: local
    external: true

You may also want to check this question here: Docker-compose - volumes driver local meaning. So, there seem to be some docker volume plugins that are made specifically for the portability reasons; such as flocker or hedvig. But I didn't use a plugin for such purpose, so I can't really recommend one, yet.