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Change The State of The Container

WARNING: This Kata is behaving strangely in when using the meta-docker approach. Be warned that your container might freeze up.

Docker Documentation References:

docker exec

docker start

docker stop

Other References:

apk

vim

Intent

The purpose of this kata is to familarize yourself with the notion that the containers disk and states is independet of the image that created it.

Overview

In this exercise we will start a container, install the vim editor, create a document, demonstrate that the document is saved on the containers disk, stop and restart the container, and demonstrate that the document is still saved on the disk. Finally we will stop the container again.

Kata Steps

Start the Container

Command

docker start docker_katas_nginx

Output

thought:DockerKata rich$ docker start docker_katas_nginx
docker_katas_nginx

Execute the apk update command

Note: This updates the images list of available packages to install

Command

docker exec docker_katas_nginx apk update

Output

thought:DockerKata rich$ docker exec docker_katas_nginx apk update
fetch http://dl-cdn.alpinelinux.org/alpine/v3.5/main/x86_64/APKINDEX.tar.gz
fetch http://dl-cdn.alpinelinux.org/alpine/v3.5/community/x86_64/APKINDEX.tar.gz
v3.5.2-84-gf3deae790a [http://dl-cdn.alpinelinux.org/alpine/v3.5/main]
v3.5.2-81-gf4d50b1370 [http://dl-cdn.alpinelinux.org/alpine/v3.5/community]
OK: 7962 distinct packages available

Execute the apk add vim command

Note: This installs vim on the running container

Command

docker exec docker_katas_nginx apk add vim

Output

thought:DockerKata rich$ docker exec docker_katas_nginx apk add vim
(1/5) Installing lua5.2-libs (5.2.4-r2)
(2/5) Installing ncurses-terminfo-base (6.0-r7)
(3/5) Installing ncurses-terminfo (6.0-r7)
(4/5) Installing ncurses-libs (6.0-r7)
(5/5) Installing vim (8.0.0329-r0)
Executing busybox-1.25.1-r0.trigger
OK: 45 MiB in 31 packages

Use vim on the container

Command

docker exec -it docker_katas_nginx vim

Note: We will disucss the -it option on exec in a later step

Output

  • You should find yourself in a vim session.
  • Insert some text and save the file using <ESC> :w simple.txt
  • Then exit vim using <ESC> :q

List files on the container to see the document you created in the prevoius step

Command

docker exec docker_katas_nginx ls

Output

thought:DockerKata rich$ docker exec -it docker_katas_nginx ls
bin         home        mnt         run         srv         usr
dev         lib         proc        sbin        sys         var
etc         media       root        simple.txt  tmp

Stop the Container

Command

docker stop docker_katas_nginx

Output

thought:DockerKata rich$ docker stop docker_katas_nginx
docker_katas_nginx

Restart the Container

Command

docker start docker_katas_nginx

Output

thought:DockerKata rich$ docker start docker_katas_nginx
docker_katas_nginx

List files on the container to see the document you created in the prevoius step

Command

docker exec docker_katas_nginx ls

Output

thought:DockerKata rich$ docker exec -it docker_katas_nginx ls
bin         home        mnt         run         srv         usr
dev         lib         proc        sbin        sys         var
etc         media       root        simple.txt  tmp

Note: that your file persisted in the conainer between stops and starts, however the image used to create this container does not contain the changes (installation of vim and the simple.txt file), so additional containers created from that image will not have these things. In the next kata we will demonstrate how to create an image from a container.

Stop the Container

Command

docker stop docker_katas_nginx

Output

thought:DockerKata rich$ docker stop docker_katas_nginx
docker_katas_nginx

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