[Docker-compose] How to use unnamed and named volumes of volumes. Bind mount

This is a personal memo.

How to use the volume specified by docker or docker-compose.

Difference between two volumes in docker-compose.yml

There is a difference between (1) outer volumes and (2) volumes in services in docker-compose.yml.


version: "3.7"

volumes:
  todo-mysql-data:

services:
  mysql:
    image: mysql:5.7
    volumes:
      - todo-mysql-data:/var/lib/mysql

Volumes in the same hierarchy as version prepares volumes with the specified name.

This is called a named volume.

volumes:
  todo-mysql-data:

--Volumes can be shared by multiple containers. --It does not disappear even if you delete the container (it does not depend on the container)

## ② volumes in services

Volumes in each service are called ** bind mount ** and are distinguished from volumes.

** Represents the process of mounting (sharing) the directory inside the container and the directory on the host side **.

services:
  mysql:
    image: mysql:5.7
    volumes:
      - todo-mysql-data:/var/lib/mysql

In the above example, the volume todo-mysql-data is mounted on / var / lib / mysql in the container.

Now you can sync the data in / var / lib / mysql to the volume.

## How to write a bind mount There are several ways to write a bind mount.

item	Bind mount	Contents
Named volume	datavolume:/var/lib/mysql	Mount the specified volume on the specified directory in the container
Anonymous volume	/var/lib/data	Specify only the directory in the container. A hash value volume is assigned. (It disappears when the container is deleted)
Share root directory(Relative path)	.:app	Mounts the specified directory in the container on the running directory on the host side.
Specified by absolute path	/opt/data:/var/lib/mysql	Mount the specified directory in the container to the specified directory on the host side.

I often see descriptions like .: App.

By doing this, the data in the container can be reproduced on the host side. (Without this, the data cannot be seen on the host side)

item	Named volume	Anonymous volume
Main applications	・(1)Sharing a volume with multiple containers (example: db)(2)Exclude from synchronization to host side(Example: node_module)	Data that you don't need to share with other containers but want to keep (eg log)
Delete container	Remains (container independent)	Disappear