Docker tutorial

Installation will take place on a Digital Ocean droplet with Ubuntu 18.04

1. Installing some tools (optional)

apt update
apt install git mc htop screen -y

2. Install docker

apt update
apt install apt-transport-https ca-certificates curl software-properties-common -y
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -
add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu bionic stable"
apt update
apt-cache policy docker-ce
apt install docker-ce -y

To test the status of docker service:

systemctl status docker

3. Run a docker image in a container

docker run hello-world

The output will be something like this

Unable to find image 'hello-world:latest' locally
latest: Pulling from library/hello-world
1b930d010525: Pull complete
Digest: sha256:41a65640635299bab090f783209c1e3a3f11934cf7756b09cb2f1e02147c6ed8
Status: Downloaded newer image for hello-world:latest

Hello from Docker!
This message shows that your installation appears to be working correctly.

To generate this message, Docker took the following steps:
 1. The Docker client contacted the Docker daemon.
 2. The Docker daemon pulled the "hello-world" image from the Docker Hub.
    (amd64)
 3. The Docker daemon created a new container from that image which runs the
    executable that produces the output you are currently reading.
 4. The Docker daemon streamed that output to the Docker client, which sent it
    to your terminal.

To try something more ambitious, you can run an Ubuntu container with:
 $ docker run -it ubuntu bash

Share images, automate workflows, and more with a free Docker ID:
 https://hub.docker.com/

For more examples and ideas, visit:
 https://docs.docker.com/get-started/

Note that the container prints the message and exists immediately.

4. Runing a docker image with interactive shell

docker run -it ubuntu

Note that any change you make in the container is persistent between the container restarts.

5. List running containers

docker ps

6. List all containers (active and inactive)

docker ps -a

7. Start a stopped container

docker start d9b100f2f636

where d9b100f2f636 is the CONTAINER ID that is listed in the docker ps -a command

8. Keep the container running

docker run -d ubuntu tail -f /dev/null

where ubuntu is the image name

9. Stop a running container

docker stop d9b100f2f636

where d9b100f2f636 is the CONTAINER ID that is listed in the docker ps -a command

docker stop -t=30 d9b100f2f636

-t=30 will allow the container to gracefully stop

10. Remove (delete) a container

docker rm d9b100f2f636

where d9b100f2f636 is the CONTAINER ID that is listed in the docker ps -a command

11. SSH into a running container

docker exec -it d9b100f2f636 /bin/bash

where d9b100f2f636 is the CONTAINER ID that is listed in the docker ps -a command

12. List available images

docker images

13. Search for images

docker search ubuntu

Default limit is 25. To list more results use --limit 100 option.
The images are listed from https://hub.docker.com/

14. Create a custom image

mkdir DOCKER-IMAGE-TEST
cd DOCKER-IMAGE-TEST
nano Dockerfile

and paste

FROM ubuntu
MAINTAINER Gigel <user@email.tld>

RUN apt-get update --fix-missing && apt-get install -y apache2

EXPOSE 80

CMD ["service", "apache2", "start"]

create the image by running

docker build -t ubuntu:apache2 .

after it completes, the images will be in the list of images

15. Delete an image

docker rmi Image

where Image is the image name

16. Clean up docker

docker system prune

It will delete images, containers, volumes, and networks — that are dangling (not associated with a container).

17. Exposing ports to the ouside of containers (local machine)

docker run -p 127.0.0.1:80:80 -d ubuntu:apache2 tail -f /dev/null

to make sure the port is exposed, run

netstat -tulnap | grep LISTEN

18. Examples

Run MariaDB server

docker run --name some-mariadb -p 127.0.0.1:3307:3306 -e MYSQL_ROOT_PASSWORD=my-secret-pw -d mariadb

the exposed MariaDB port used is 3307. to check it, run netstat -tulnap | grep LISTEN

to login to MariaDB server, run:

mysql -P 3307 -h 127.0.0.1 -u root -p

to SSH into the Docker container, run:

docker exec -it some-mariadb bash

more info https://hub.docker.com/_/mariadb

Useful links

• https://www.digitalocean.com/community/tutorials/how-to-install-and-use-docker-on-ubuntu-18-04
• http://phase2.github.io/devtools/common-tasks/ssh-into-a-container/
• https://www.digitalocean.com/community/tutorials/how-to-share-data-between-the-docker-container-and-the-host
• https://www.mirantis.com/blog/how-do-i-create-a-new-docker-image-for-my-application/
• https://www.digitalocean.com/community/tutorials/how-to-remove-docker-images-containers-and-volumes
• https://stackoverflow.com/questions/30209776/docker-container-will-automatically-stop-after-docker-run-d/46898038
• https://serverfault.com/questions/924779/docker-cron-not-working
• https://github.com/francarmona/docker-ubuntu16-apache2-php7/blob/master/Dockerfile
• https://github.com/laradock/laradock
• https://github.com/wsargent/docker-cheat-sheet