Docker creates a new volume everytime I do docker compose up

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I have a docker-compose file that spins up several services. I just got an error stating I ran out of disk space so I typed "docker system df" and saw I have 21 volumes. If I have 3 docker containers with each having a volume attached to them, why its showing me a total count of 21 volumes?

I am using AWS EC2. This is my compose file, is there anything wrong with the way I have the volumes set? The postgres data got persisted when I shutdown and restart, I am just confused aboutthe volume size and the message that I can not rebuild due to no space on a T2 Large instance.

version: "3"
services:
  nftapi:
    env_file:
      - .env
    build:
      context: .
    ports:
      - '443:5000'
    depends_on: 
      - postgres
    volumes: 
      - .:/app
      - /app/node_modules
    networks:
      - postgres
      
  postgres:
    container_name: postgres
    image: postgres:latest
    ports:
    - "5432:5432"
    volumes:
    - /data/postgres:/data/postgres
    env_file:
    - docker.env
    networks:
    - postgres
 
  pgadmin:
    links:
    - postgres:postgres
    container_name: pgadmin
    image: dpage/pgadmin4
    ports:
    - "8080:80"
    volumes:
    - /data/pgadmin:/root/.pgadmin
    env_file:
    - docker.env
    networks:
    - postgres
 
networks:
  postgres:
    driver: bridge

enter image description here

docker amazon-web-services amazon-ec2
2 Answers

if your main containers are up and running run

docker volume prune

and it should remove any volumes that are detached or unused by any container i make it a habit to run periodically on my aws instance

docker system prune
user_93735970

A Docker image's Dockerfile can contain a VOLUME directive. This is an instruction to Docker that tells it that some container directory contains data that needs to be persisted, and Docker should always ensure a volume of some sort is mounted on that directory.

More specifically, the postgres image declares

VOLUME /var/lib/postgresql/data

Your Compose setup doesn't mount anything on that specific directory. Because of this, Docker creates an anonymous volume and mounts it there for you. This isn't specific to the postgres image and other containers in your stack may have similar local data directories. Those anonymous volumes are what you're seeing in the docker system df output (docker volume ls will also show them).

In a later question you also note that Compose has trouble finding these anonymous volumes, and it's better to not rely on this functionality. Make sure you're mounting a host directory or named volume for these data directories via Compose volumes:.

user_100081730
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