Skip to content

Volumes

Jump to bottom
Rodrigo edited this page Jul 8, 2020 · 3 revisions

There are two kinds of data:

  • Persistent: It's that information we want to keep, for instance, if we have a MySQL database, we want to save all our records.
  • Non-persistent: Non-relevant information. cache, logs, and so on.

By default, every container has its own non-persistent storage (most OS use overlay2 and it stores container information under /var/lib/docker/storage-driver/)

However, we can create volumes and persist our data. How ?

The following command to create a new volume called my-first-volume:

vagrant@ubuntu-xenial:~$ docker volume create my-first-volume
my-first-volume

vagrant@ubuntu-xenial:~$ docker volume ls
DRIVER              VOLUME NAME
local               my-first-volume

vagrant@ubuntu-xenial:~$ docker volume inspect my-first-volume
[
 {
  "CreatedAt": "2019-09-28T09:47:37Z",
  "Driver": "local", ---> By default, Docker creates new volumes with local driver, they are only available on the node they were created 
  "Labels": {},
  "Mountpoint": "/var/lib/docker/volumes/my-first-volume/_data",
  "Name": "my-first-volume",
  "Options": {},
  "Scope": "local"
 }
]

Now, we are going to attach this volume to a container and create a file (test-volume.txt) under path /data:

vagrant@ubuntu-xenial:~$ docker container run -d -it --name test-volume-alpine --mount source=my-first-volume,target=/data alpine 
b7bf95e4a4c2c44a77b1cb6cf083a9958b2b91aff4c826dc71d2d48efe98189d

vagrant@ubuntu-xenial:~$ docker container exec -ti test-volume-alpine /bin/sh
/ # ls
bin    data   dev    etc    home   lib    media  mnt    opt    proc   root   run    sbin   srv    sys    tmp    usr    var
/ # cd data/
/data # ls
/data # echo "Hello World" > test-volume.txt

We leave of our Alpine container (Ctrl-PQ) and verify if test-volume.txt was created under /var/lib/docker/volumes/my-first-volume/_data:

vagrant@ubuntu-xenial:~$ sudo -i

root@ubuntu-xenial:~# cd /var/lib/docker/volumes/my-first-volume/_data

root@ubuntu-xenial:/var/lib/docker/volumes/my-first-volume/_data# ls
test-volume.txt

root@ubuntu-xenial:/var/lib/docker/volumes/my-first-volume/_data# cat test-volume.txt 
Hello World

root@ubuntu-xenial:/var/lib/docker/volumes/my-first-volume/_data# exit
logout

On the other hand, a volume can be shared, for instance, we are going to run another container in order to access to same volume:

vagrant@ubuntu-xenial:~$ docker container run -d -it --name test-volume-alpine2 --mount source=my-first-volume,target=/data alpine 
5d31ea3a636e2858c39cd40fa52cb27b859c60c425ac6b6abfa968f1a90a9962

vagrant@ubuntu-xenial:~$ docker container exec -ti test-volume-alpine /bin/sh
/ # cd data/
/data # ls
test-volume.txt
/data # cat test-volume.txt 
Hello World
/data # read escape sequence

Do you want remove these volumes?, there are two commands to remove volumes:

  • docker volume prune: Delete all volumes that are not mounted into a container (be careful).
  • docker volume rm: Specify which volume you want to delete.
vagrant@ubuntu-xenial:~$ docker container stop test-volume-alpine
test-volume-alpine

vagrant@ubuntu-xenial:~$ docker container stop test-volume-alpine2
test-volume-alpine2

vagrant@ubuntu-xenial:~$ docker container rm test-volume-alpine
test-volume-alpine

vagrant@ubuntu-xenial:~$ docker container rm test-volume-alpine2
test-volume-alpine2

vagrant@ubuntu-xenial:~$ docker volume rm my-first-volume 
my-first-volume

Finally, I am going to show a case that is often used with Docker when it comes to test.

First of all, we create a Nginx container and expose its port:

vagrant@ubuntu-xenial:~$ docker container run -d -p 8080:80 --name nginx nginx
vagrant@ubuntu-xenial:~$ curl localhost:8080
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
    body {
        width: 35em;
        margin: 0 auto;
        font-family: Tahoma, Verdana, Arial, sans-serif;
    }
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>

<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>

<p><em>Thank you for using nginx.</em></p>
</body>
</html>

Secondly, we are going to change Nginx home page:

docker container stop nginx

docker container rm nginx

We create a new index.html:

cat <<EOF >index.html
<!DOCTYPE html>
<html>
 <head>
  <title>Nginx home</title>
  <style>
   body { width: 35em; margin: 0 auto; font-family: Tahoma, Verdana, Arial, sans-serif; }
  </style>
 </head>
 <body>
  <h1>Hello World</h1>
 </body>
</html>
EOF

We run Nginx container by using -v parameter where we specify to mount a file (index.html) under a particular path (/usr/share/nginx/html/index.html):

vagrant@ubuntu-xenial:~$ echo $PWD
/home/vagrant

vagrant@ubuntu-xenial:~$ ls
index.html

vagrant@ubuntu-xenial:~$ docker container run --name nginx -d -p 8080:80 -v $PWD/index.html:/usr/share/nginx/html/index.html nginx
6188219f7a74ca197daf775ca87be0c489f365eea54b96b04c7ca65275a40e38
vagrant@ubuntu-xenial:~$ curl localhost:8080
<!DOCTYPE html>
<html>
 <head>
  <title>Nginx home</title>
  <style>
   body { width: 35em; margin: 0 auto; font-family: Tahoma, Verdana, Arial, sans-serif; }
  </style>
 </head>
 <body>
  <h1>Hello World</h1>
 </body>
</html>

Tidying up:

vagrant@ubuntu-xenial:~$ docker container stop nginx
nginx

vagrant@ubuntu-xenial:~$ docker container rm nginx
nginx

vagrant@ubuntu-xenial:~$ docker image rm $(docker image ls -qa)
Untagged: nginx:latest
Untagged: nginx@sha256:aeded0f2a861747f43a01cf1018cf9efe2bdd02afd57d2b11fcc7fcadc16ccd1
Deleted: sha256:f949e7d76d63befffc8eec2cbf8a6f509780f96fb3bacbdc24068d594a77f043
Deleted: sha256:301c5d89cad94a6a99703841b021cf7df4326d2f14715c52b4b27893b13e02c0
Deleted: sha256:c3172409dcf95530cce7aad6a4c16a476fec9c43ac38426e9487b43efd246357
Deleted: sha256:2db44bce66cde56fca25aeeb7d09dc924b748e3adfe58c9cc3eb2bd2f68a1b68
Untagged: alpine:latest
Untagged: alpine@sha256:72c42ed48c3a2db31b7dafe17d275b634664a708d901ec9fd57b1529280f01fb
Deleted: sha256:961769676411f082461f9ef46626dd7a2d1e2b2a38e6a44364bcbecf51e66dd4
Deleted: sha256:03901b4a2ea88eeaad62dbe59b072b28b6efa00491962b8741081c5df50c65e0

vagrant@ubuntu-xenial:~$ rm index.html
Clone this wiki locally