ChamplainTechJournals/sysadmin-ii-sys265/labs/lab03-docker.md

Containerization with Docker

set up docker01 - Ubuntu 20.04 cloud server

IP Address: 10.0.5.12 (change web01 address to 10.0.5.20)
Default Gateway: 10.0.5.2
DNS: 10.0.5.5

changing hostname. it is different on Ubuntu Cloud

• in /etc/cloud/cloud.cfg:

preserve_hostname: true
hostname: docker01-charlotte (add this line under)
fqdn: docker01-charlotte.charlotte.local (add this line under)

• change hostname for 127.0.1.1 in /etc/hosts file

• finally, sudo hostnamectl hostname docker01-charlotte
• update DNS records on mgmt01 (remember to change web01 record too)

docker installation

https://www.digitalocean.com/community/tutorials/how-to-install-and-use-docker-on-ubuntu-20-04

update and install prerequisite packages, this will let apt use packages over HTTPS

sudo apt update
sudo apt install apt-transport-https ca-certificates curl software-properties-common

add the GPG key

curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -

add docker repo to APT sources

sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu focal stable"

validate installation is from docker repo. Notice that docker-ce is not installed, but the candidate for installation is from the Docker repository for Ubuntu 20.04 (focal).

apt-cache policy docker-ce | head

install docker

sudo apt install docker-ce

check status

sudo systemctl status docker

executing the docker command without sudo:

add user to the docker group, apply the new group membership, and logout/log back in

sudo usermod -aG docker charlotte
su - charlotte

using docker

downloading images

search for images availabe on Docker Hub

docker search <image-name>

download from Dockuer Hub

docker pull <image-name>

see installed images

docker images

docker-compose

• https://www.digitalocean.com/community/tutorials/how-to-install-and-use-docker-compose-on-ubuntu-20-04

"Docker Compose is a tool that allows you to run multi-container application environments based on definitions set in a YAML file."

download the 1.29.2 release and save the executable file at /usr/local/bin/docker-compose

sudo curl -L "https://github.com/docker/compose/releases/download/1.29.2/docker-compose-$(uname -s)-$(uname -m)" -o /usr/local/bin/docker-compose

make docker-compose executable:

sudo chmod +x /usr/local/bin/docker-compose

verify installation

docker-compose --version

The following command pulls down an Arch Linux based docker image, invokes it in a container, and runs /bin/echo "HELLO SYS265 SNOWY DAYS '' before deleting the container.

docker run --rm archlinux:latest /bin/echo "HELLO SYS265 SNOWY DAYS"

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docker run command syntax (example)

• e.g. The following command will pull down the image, application and dependencies associated with a simple python web application. docker run -d -P training/webapp python app.py

• docker: CLI for interacting with docker

• run: create and start a new container

• -d (or --detach): the container runs in the background.

  • useful for non-interactive services, like webservers and databases

• -P (or --publich-all): automatically publishes all exposed ports of the container to random host ports.

  • This allows external access to the services running in the container without having to specify port mappings manually.

• training/webapp: the docker image from which the container is created

  • In this case, an image named webapp that is located in the training repository

• python: command that will be executed inside the container once it starts

• app.py: argument passed to the python command

  • the Python script app.py should be executed by the Python interpreter when the container starts.

• docker run httpd will automatically set up an apache web server in the container

to stop docker process

docker stop <container ID>

dockerized WordPress

https://github.com/docker/awesome-compose/tree/master/wordpress-mysql

• create a directory docker-wp
• create compose.yml

Caution

Absolutely never use a tab in a docker-compose.yml file

services:
  db:
    # We use a mariadb image which supports both amd64 & arm64 architecture
    image: mariadb:10.6.4-focal
    # If you really want to use MySQL, uncomment the following line
    #image: mysql:8.0.27
    command: '--default-authentication-plugin=mysql_native_password'
    volumes:
      - db_data:/var/lib/mysql
    restart: always
    environment:
      - MYSQL_ROOT_PASSWORD=somewordpress
      - MYSQL_DATABASE=wordpress
      - MYSQL_USER=wordpress
      - MYSQL_PASSWORD=wordpress
    expose:
      - 3306
      - 33060
  wordpress:
    image: wordpress:latest
    ports:
      - 80:80
    restart: always
    environment:
      - WORDPRESS_DB_HOST=db
      - WORDPRESS_DB_USER=wordpress
      - WORDPRESS_DB_PASSWORD=wordpress
      - WORDPRESS_DB_NAME=wordpress
volumes:
  db_data:

• docker compose up -d
• wait...it's really that easy?
  • yes

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showing how containers use the same kernel as the host

• example: the following commands will:
  • Print out the current version of Ubuntu on docker01. cat /etc/lsb-release
  • Print out the current version of docker01's linux kernel. echo "Current Kernel is: $(uname -a)"
  • Invoke a container of the stored Ubuntu image as well as an interactive bash command prompt, and print out the kernel being used by the Ubuntu container. docker run -it archlinux /bin/uname -a
• as you can see, both the docker container(archlinux) and the host(docker01-charlotte) are using the same kernels