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Docker

🌐 Resources 🔗

Docker Architecture

Container - a way to package application will all the necessary dependencies and configuration

  • portable standardized artifact for efficient development and deployment

    • Devs & Ops work together to package the app in a container

    • No environment config needed on server (only Container Runtime)

  • layers of images

    • Linux base image

    • other layers

    • Application image

Container repositories

Docker - open source containerization platform

Docker image - the actual package file, artifact, consisting of layers

Docker container - started application, a running environment, virtual file system, port binding

Virtual machines - virtualize the OS Kernel and the Application layer - full copy of the OS, abstraction of physical hardware

Containers - multiple containers share the OS Kernel - abstraction of the app layer

Docker Engine

Docker Engine acts as a client-server application with:

  • Server - dockerd, managing images & containers

    • Container Runtime

    • Volumes

    • Network

    • build images

  • API - interact with Docker Server

  • CLI - docker client

Docker Network

Libnetwork implements Container Network Model (CNM) which formalizes the steps required to provide networking for containers while providing an abstraction that can be used to support multiple network drivers.

docker network ls
    NETWORK ID     NAME      DRIVER    SCOPE
    964fd24a27a1   bridge    bridge    local
    446ad1bfc60e   host      host      local
    d1be7e105231   none      null      local

Docker Compose

Docker Compose - define and run multiple docker containers applications

  • yaml file to configure application's services

  • easy maintenance and config

Dockerfile

Dockerfile - text file with instructions to build Docker images

  • each instruction results in an image layer

  • used in CI/CD to build the docker image artifact, pushed to Docker (remote or local) repositories

  • each image is based on another base image (FROM <image>)

Dockerfile

FROM <image>

# Comment
INSTRUCTION arguments

# e.g.
ENV SOME_ENV=value

# run commands inside the container
RUN mkdir -p /home/app

RUN ...

# copy files from host to container
COPY . /home/app

# entrypoint command
CMD ["command","arguments"]

Docker Repositories

Public repositories

Public repositories (container registries)

Image naming in Docker - registryDomain/imageName:tag

# e.g. DockerHub
docker pull docker.io/library/ubuntu # default
# same as
docker pull ubuntu

# e.g. Push image to private my-repo
# Login to private my-repo
docker tag <my-repo/my-app:version>
docker push <my-repo/my-app:version>

Docker Volumes

Volumes - persist container generated and used data, by mounting a folder from the physical host file system into the Docker virtual file system

  • databases

  • stateful applications

  • data automatically replicated

  • Host, Anonymous, Named volumes

Host Path - /var/lib/docker/volumes

Docker Engine Install - Ubuntu Linux

# Install Docker Engine via APT repository

for pkg in docker.io docker-doc docker-compose docker-compose-v2 podman-docker containerd runc; do sudo apt-get remove $pkg; done

sudo apt update -y && sudo apt install -y ca-certificates curl gnupg

sudo sh -c '
    curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /usr/share/keyrings/docker.gpg
    sudo chmod a+r /usr/share/keyrings/docker.gpg

    echo "deb [arch="$(dpkg --print-architecture)" signed-by=/usr/share/keyrings/docker.gpg] https://download.docker.com/linux/ubuntu "$(. /etc/os-release && echo "$VERSION_CODENAME")" stable" | sudo tee /etc/apt/sources.list.d/docker.list

    sudo apt update && sudo apt install -y docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin
'

sudo systemctl enable docker --now
sudo gpasswd -a "${USER}" docker

# On Debian and Ubuntu, the Docker service starts on boot by default, if not run
sudo systemctl enable docker.service
sudo systemctl enable containerd.service

# Reboot and Test
reboot
docker run hello-world

Commands

docker pull <image>

# e.g.
docker pull postgres
docker pull ubuntu
docker pull alpine
docker pull redis
# without tag, the latest version is downloaded

docker run <image>
# detached mode
docker run -d <image> 

# use containers
docker start <container_id>
docker stop <container_id>

docker images
docker ps
# list running and exited containers
docker ps -a

# e.g. with image:tag
docker run redis:4.0

# Map a free port on HOST machine
docker run -p6000:6379 -d redis
docker run -p6001:6379 -d redis:4.0

# fetch logs
docker logs <container_id>
docker logs <container_id> -f
docker logs <container_name>

# name a container
docker run -p6000:6379 -d --name redis-latest redis

# new bash session in the container
docker exec -it <container_id> /bin/bash
docker exec -it <container_id> /bin/sh
docker network ls

# e.g.
docker network create test-network
docker compose -f docker-compose.yaml up
docker compose -f docker-compose.yaml down
# Build Dockerfile
docker build -t my-app:1.0 .

# Remove containers and images
docker rm <container_id>
docker rmi <image_id>
# Push to container registry

docker login
- reponame
- username
- password

docker tag <repo-name>:<image-version>
docker push <tagged-image>

docker pull <repo-name>:<image-version>
# registryDomain/imageName:tag
# Named Volumes
docker run -v name:/var/lib/mysql/data

# Host Volumes
docker run -v /home/mount/data:/var/lib/mysql/data

# Anonymous Volumes
docker run -v /var/lib/mysql/data

Labs

git clone https://gitlab.com/nanuchi/developing-with-docker.git
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