Data Volumes

• Can be specified in Dockerfile with VOLUME
• They outlive container/image -- they need to be removed manually

VOLUME /var/lib/mysql   # example from official mysql image

Can be also seen in image metadata

~> docker image inspect mysql
    ...
    "Volumes": {
        "/var/lib/mysql": {}
    },
    ...

Or in container metadata

~> docker container inspect mysql
    ...
    "Mounts": [
        {
            "Type": "volume",
            "Name": "60afa8e3350f96256e33a8459b4af4742a45d102ee09d527dd5e44a1fc46d626",
            "Source": "/var/lib/docker/volumes/60afa8e3350f96256e33a8459b4af4742a45d102ee09d527dd5e44a1fc46d626/_data",
            "Destination": "/var/lib/mysql",
            "Driver": "local",
            "Mode": "",
            "RW": true,
            "Propagation": ""
        }
    ],
    "Config": {
    ...
        "Volumes": {
            "/var/lib/mysql": {}
        },
    ...

List volumes and details

~> docker volume ls
DRIVER              VOLUME NAME
local               60afa8e3350f96256e33a8459b4af4742a45d102ee09d527dd5e44a1fc46d626

~> docker volume inspect 60afa8e3350f96256e33a8459b4af4742a45d102ee09d527dd5e44a1fc46d626
[
    {
        "Driver": "local",
        "Labels": null,
        "Mountpoint": "/var/lib/docker/volumes/60afa8e3350f96256e33a8459b4af4742a45d102ee09d527dd5e44a1fc46d626/_data",
        "Name": "60afa8e3350f96256e33a8459b4af4742a45d102ee09d527dd5e44a1fc46d626",
        "Options": {},
        "Scope": "local"
    }
]

Prove that data are safe

# check that we have active container and volume
~> docker container ls
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS        NAMES
2b4303ca2b09        mysql               "docker-entrypoint..."   15 minutes ago      Up 15 minutes       3306/tcp     mysql

# check that we have a volume
~> docker volume ls
DRIVER              VOLUME NAME
local               60afa8e3350f96256e33a8459b4af4742a45d102ee09d527dd5e44a1fc46d626

# remove a container
~> docker container rm -f mysql

# check that no container left
~> docker container ls
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS        NAMES

# volume is still present
~> docker volume ls
DRIVER              VOLUME NAME
local               60afa8e3350f96256e33a8459b4af4742a45d102ee09d527dd5e44a1fc46d626

Named volumes

• Friendly way to assign volumes to containers
• -v name:path

~> docker container run -d --name mysql -e MYSQL_ALLOW_EMPTY_PASSWORD=true -v mysql-db:/var/lib/mysql mysql
8b27c98f1365c834e64dba06d948126fd87e7a49a4902937e732b7ab6cdcbc59

~> docker volume ls
DRIVER              VOLUME NAME
local               60afa8e3350f96256e33a8459b4af4742a45d102ee09d527dd5e44a1fc46d626
local               mysql-db

~> docker volume inspect mysql-db
[
    {
        "Driver": "local",
        "Labels": null,
        "Mountpoint": "/var/lib/docker/volumes/mysql-db/_data",
        "Name": "mysql-db",
        "Options": {},
        "Scope": "local"
    }
]

• Reusing -v name:path doesn't create new volume, but attach to existing one

~> docker container run -d --name mysql2 -e MYSQL_ALLOW_EMPTY_PASSWORD=true -v mysql-db:/var/lib/mysql mysql
0896580e6313ac6fa9b94956e3ccdf301fd6e98dc0f73302632738c7e45a582c

~> docker volume ls
DRIVER              VOLUME NAME
local               60afa8e3350f96256e33a8459b4af4742a45d102ee09d527dd5e44a1fc46d626
local               mysql-db

docker volume create

• required to do this before "docker run" to use custom drivers and labels