docker-compose save/load images to another host

Question

I have found this, but it does not work for me.

My (really) simple docker-compose.yml:

version: '3.1'

services:

  wordpress:
    image: wordpress
    restart: always
    ports:
      - 8080:80
    environment:
      WORDPRESS_DB_PASSWORD: example

  mysql:
    image: mysql:5.7
    restart: always
    environment:
      MYSQL_ROOT_PASSWORD: example

Starting:

docker-compose up

After made some change to containers (install plugins and themes on wordpress).

docker-compose stop
docker commit main_mysql_1 test-mysql
docker commit main_wordpress_1 test-wordpress
docker save test-mysql > test-mysql.tar
docker save test-wordpress > test-wordpress.tar

Save the two tar files on another machine and load them:

docker load -i ./test-mysql.tar
docker load -i ./test-wordpress.tar

Now change the docker-compose.yml to:

version: '3.1'

services:

  wordpress:
    image: test-wordpress
    restart: always
    ports:
      - 8080:80
    environment:
      WORDPRESS_DB_PASSWORD: example

  mysql:
    image: test-mysql
    restart: always
    environment:
      MYSQL_ROOT_PASSWORD: example

But the container started is wordpress from scratch. Nothing of work done (plugin, themes, etc) was preserved.

What is my mistake? I don't want to use online repository for these private purposes.. Could you suggest a more simple and powerful procedure for pass container between two hosts?

---

A workaround with volumes:

version: '3.1'

services:

  wordpress:
    container_name: GREB_wordpress      
    image: wordpress
    restart: always
    ports:
      - 8080:80
    environment:
      WORDPRESS_DB_PASSWORD: example
    volumes:
      - ./www:/var/www/html  

  mysql:
    container_name: GREB_mysql
    image: mysql:5.7
    restart: always
    environment:
      MYSQL_ROOT_PASSWORD: example
    volumes:
      - ./mysql_data:/var/lib/mysql  

Answer 1

First of all, docker volumes are not part of an image and/or a container. So these should be saved further the docker images (docker save).

For a better understanding of docker file system, volumes, ro/rw layer, could be read http://container-solutions.com/understanding-volumes-docker/.

Figure out if our image use volumes (seek "Volumes" key):

docker inspect image_name

You have different advantage to use volumes (refer to docker documentation for well understand) such as I/O performance.

A the end, for backup volumes:

• Simply backup volumes folder e.g. tar -cvzPf volume_name_backup.tar.gz /var/lib/docker/volumes/VOLUME_NAME...and restore them in the same place
• Backup, restore, or migrate data volumes through another docker container
• In case of db image (like my case with mysql) you can also dump the db: docker exec mysql_container /usr/bin/mysqldump -u root --password=root --all-databases > mysql_dump_backup.sql