Mount host path

 

  • -v has yet another major use case, which can only be accomplished through -v option.
  • Mount the host directory into container.
  • docker run -v @host_path:@container_path -it busybox
    • host path must be absolute.
    • container path is absolute as well.
docker run -v $(pwd)/volume/:/my-volume -it busybox
  • We can use $(pwd) to get absolute path for current directory.
  • With above command, we are mounting /volume directory that relative to where build process was started.

Simple example

  • Let's try this with busybox first.
  • docker run -v $(pwd)/volume/:/my-volume -it busybox
  • Create a file under /my-volume inside the container.
  • You will see that file in host directory as well, under "CURRENT_DIR"/volume.

Using volume for persistence storage

  • Using volume on these case doesn't make sense.
  • We are creating a file and checking if it exists in subsequent runs.
  • But consider this scenario when you run mysql image.
  • You would want to persist the data that you created inside container.
  • It doesn't matter how many times you restart your container, we must not lose the data.

Using to persist mysql data

  • mysql stores its data inside /var/lib/mysql/.
  • So if we map our host path with /var/lib/mysql/, we will be able to persist mysql data.
  • If you try to run the mysql image it expects couple of Environment Variable.
    • MYSQL_ROOT_PASSWORD
    • MYSQL_DATABASE
docker run \
       -v $(pwd)/volume/mysql-data:/var/lib/mysql/ \
       -e MYSQL_ROOT_PASSWORD=test \
       -e MYSQL_DATABASE=test \
       mysql:5.7

I am using -e options to pass in Environment Variables to container.

  • I am deliberately not passing -it when running container.
  • Default CMD for mysql image is used for starting mysql
  • If we override it my passing Shell executable, to attach the pseudo tty, it won't start the mysql.
  • After container is running, we can attach container tty into host terminal.
  • You already learned this but in case you forgot. To attach the pseudo tty for a running container we use docker container exec -it @container(id/name) sh
docker container exec -it 750d0ddbbe51 sh
  • Login to mysql from container terminal.
  • Create a table and insert some data into that table.
> mysql -u root -p

mysql> USE test;
Database changed

mysql> CREATE TABLE student(id INT(11), name VARCHAR(255));
Query OK, 0 rows affected (0.02 sec)

mysql> INSERT INTO student VALUES (1, 'Aman');
Query OK, 1 row affected (0.01 sec)

mysql> SELECT * FROM student;
+------+------+
| id   | name |
+------+------+
|    1 | Aman |
+------+------+
1 row in set (0.00 sec)
  • Now you stop the running container and run a new one, with same path ($(pwd)/volume/mysql-data) mapped to /var/lib/mysql/
  • You will see data is still present.
docker run \
     -v $(pwd)/volume/mysql-data:/var/lib/mysql/ \
     -e MYSQL_ROOT_PASSWORD=test \
     -e MYSQL_DATABASE=test \
     mysql:5.7