Volumes are managed by Docker and is the preferred way of persisting, sharing data.
Key Points#
- Volume drivers allows to
- Store volumes on remote hosts or cloud providers,
- Encrypt the contents of volumes.
- Volumes does not increase the size of the containers using it.
- Volume’s contents exist outside the lifecycle of a given container.
root@docker>docker volume ls
DRIVER VOLUME NAME
local c9ad85b13e22062f4eeefd9b65ae102c19856bea73622189f1a3393727c9b3e7Options to define volumes#
One an define a volume using either -v or --mount.
--mount#
Option --mount is more explicit and allows one to avoid mistakes.
It consists of multiple key-value pairs, separated by commas and each consisting of a
<key>=<value>tuple.
The option type can be either of
- volume
- bind
- tempfs
-v or --volume#
The order of information provided is very important for this option.
-vor--volumeConsists of three fields, separated by colon characters (:).
root@docker>docker volume
Usage: docker volume COMMAND
Manage volumes
Commands:
create Create a volume
inspect Display detailed information on one or more volumes
ls List volumes
prune Remove all unused local volumes
rm Remove one or more volumes
Run 'docker volume COMMAND --help' for more information on a command.Experiment time#
You can simply create a volume without specifying any name
root@docker>docker volume create
502f4ffc940ead1fc8cfaed65a9829b17aac322f9b4125b57e3a2e66f113a658docker volume ls will return the listing which will show the volume just created.
You can give name to volumes too.
root@docker>docker volume create my-volume
my-volumeroot@docker>docker volume ls
DRIVER VOLUME NAME
local my-volumeroot@docker>docker volume inspect my-volume
[
{
"CreatedAt": "2020-07-31T07:06:07Z",
"Driver": "local",
"Labels": {},
"Mountpoint": "/var/lib/docker/volumes/my-volume/_data",
"Name": "my-volume",
"Options": {},
"Scope": "local"
}
]deleting a volume is equally simple
root@docker>docker volume rm my-volume
my-volumeHow about attaching a volume to a container?
Step 1: Create a volume#
root@docker>docker volume create myvol
myvol
root@docker>docker volume ls
DRIVER VOLUME NAME
local myvolStep 2: Refer to the volume#
docker run -d --mount src=myvol,dst=/app --name my_nginx nginx:latestUnable to find image 'nginx:latest' locally
latest: Pulling from library/nginx
6ec8c9369e08: Pull complete
d3cb09a117e5: Pull complete
7ef2f1459687: Pull complete
e4d1bf8c9482: Pull complete
795301d236d7: Pull complete
Digest: sha256:0e188877aa60537d1a1c6484b8c3929cfe09988145327ee47e8e91ddf6f76f5c
Status: Downloaded newer image for nginx:latest
cee753ad7a48ccd4b1039391f7c10e8b710404472fce82e474319760e65bc89fInspecting the image can show the mount
root@docker>docker container inspect my_nginx"Mounts": [
{
"Type": "volume",
"Name": "myvol",
"Source": "/var/lib/docker/volumes/myvol/_data",
"Destination": "/app",
"Driver": "local",
"Mode": "z",
"RW": true,
"Propagation": ""
}
]If you look carefully there is a RW property which can be defined as false if you use the option ro, readonly in the option.
root@docker>ls -als /var/lib/docker/volumes/myvol/_data
total 0
0 drwxr-xr-x. 2 root root 6 Jul 31 07:12 .
0 drwxr-xr-x. 3 root root 19 Jul 31 07:12 ..Inspecting the volume myvol
root@docker>docker inspect myvol
[
{
"CreatedAt": "2020-07-31T07:12:00Z",
"Driver": "local",
"Labels": {},
"Mountpoint": "/var/lib/docker/volumes/myvol/_data",
"Name": "myvol",
"Options": {},
"Scope": "local"
}
]The syntax in the --mount can be simplified by using --volume
docker run -d -v myvol:/app --name my_nginx nginx:latestPlease note if you are creating service you have to use the --mount option as the -v is not supported for docker service create
local volume driver
