Docker

Docker is a software available since 2013 that among other features performs operating-system-level virtualization also known as containerization

Features

Docker offer the following features:

• Package an application and its dependencies in a virtual container that can run on any Linux server (docker images)
• Pull or push docker images to a container repository/container registry (docker pull, docker push). By default docker hub but you can specify any other registry.

Installing Docker

You can read official Docker documentation about installing Docker on your system: https://docs.docker.com/install/.

On macOS you can follow official documentation https://docs.docker.com/docker-for-mac/install/ which requires to create and account to download installer. You can also try: brew cask install docker or try to follow https://pilsniak.com/how-to-install-docker-on-mac-os-using-brew/ instructions:

brew install docker docker-compose docker-machine(to install docker and docker-compose)

brew cask install virtualbox

docker-machine create --driver virtualbox default

docker-machine ls

docker-machine env default

eval $(docker-machine env default)

docker run hello-world (will pull hello-world image and run it on docker)

On Ubuntu: snap install docker (officially provided by Canonical)

Binaries

Following binaries will be installed: docker-init, docker-proxy, docker and dockerd

Verifying Docker installation

Once installed the Docker daemon, called "dockerd" should be running. You can also run docker run hello-world to verify docker correct installation.

Configuration files

• Ubuntu: /etc/docker/daemon.json

Docker Releases (Docker Engine release notes)

• https://docs.docker.com/engine/release-notes/
• https://github.com/docker/docker-ce/releases

Use: docker version to check your version. You can download Docker CE source code from GitHub.

Docker Command Line

You can read official docker command line documentation in https://docs.docker.com/engine/reference/commandline/docker/. Before being able to run docker commands you will have to install Docker on your machine.

Some typical task using containers:

Docker verification commands

• Verify correct installation: docker run hello-world

You will see some message similar to this one:

Unable to find image 'hello-world:latest' locally
latest: Pulling from library/hello-world
ca4f61b1923c: Pull complete
Digest: sha256:97ce6fa4b6cdc0790cda65fe7290b74cfebd9fa0c9b8c38e979330d547d22ce1
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://cloud.docker.com/

For more examples and ideas, visit:
 https://docs.docker.com/engine/userguide/

Docker image and container creation

• Create a new docker image base on alpine linux distribution and login into the new container: docker run -it alpine sh
• Create a new docker image: docker build
  • Create a new docker image by creating a new text file with instructions, usually called Dockerfile: docker build -f /path/to/a/Dockerfile .
• Create a container: docker create
• Generate a mediawiki:1.27 image: docker build --tag mediawiki:1.27 . (you can use -t or --tag)
• Execute or run a container based on mediawiki:1.27 image: docker run --name wikiFGA -p 0.0.0.0:9090:80 -d mediawiki:1.27

Docker Container Operation

• Start an existing container: docker start CONTAINER_ID OR CONTAINER_NAME. See also docker run and differences.
• Stop an running container: docker stop container_id

• Show only running containers:
  • docker container ls or docker ps . (docker container ls) introduced in 2017 in Docker 1.13 (There is no difference between both commands)

• Show containers (running or not):
  • docker ps -a : https://docs.docker.com/engine/reference/commandline/ps/
  • docker container ls -a . See also docker-compose ps

• Login/Connect into a running container:
  • docker exec -it <my_container_name> bash
  • docker exec -it <my_container_name> sh

• Start stopped containers: docker start $(docker ps -a -q -f status=exited)
• Restart all containers: docker restart $(docker ps -aq) previously docker restart $(docker ps -q)-a all -q quiet

• Start configuration behavior and restart policy

• docker container update

See also: docker compose and docker stack

Docker images management

• List created images: docker images, docker image ls (both commands seems to perform the same action, note it is image instead of images)
• Images are stored in docker info | grep "Docker Root Dir"
• docker image rm. See also: docker rm CONTAINER
• docker rmi IMAGE_ID

Docker Network command line commands

• docker network ls
• docker network inspect
• Deprecated: docker --link
• docker network create NETWORK_NAME

Docker resource limitation

• Limit container CPU usage to 0.5 cpus: docker run -it --cpus=".5" docker_image /bin/bash
• Limit memory requires your kernel to have functionality activated, you can check it executingdocker info. See https://docs.docker.com/install/linux/linux-postinstall/ and docker-compose resource limitation example: Version 3 resouces

Docker: Working with remote repositories/registries

You will be using mainly the following commands docker login, docker logout, docker pull and docker push. Docker registry allow to configure notifications. . Docker has a public repository called Docker Hub and cloud providers offer repositories services such as AWS Elastic Container Registry (ECR).

Docker Information

• docker version https://docs.docker.com/engine/reference/commandline/version/
• docker info https://docs.docker.com/engine/reference/commandline/info/
• docker stats https://docs.docker.com/engine/reference/commandline/stats/
• docker system info https://docs.docker.com/v17.12/edge/engine/reference/commandline/system_info/
• docker system events https://docs.docker.com/v17.12/edge/engine/reference/commandline/system_events/
• docker system df
• docker top [CONTAINER_NAME or CONTAINER_ID] https://docs.docker.com/engine/reference/commandline/top/
• docker inspect CONTAINER_ID|IMAGE_ID https://docs.docker.com/engine/reference/commandline/inspect/ also available for: container, image, volume, network, node, service, or task
• docker images, docker images -q
• docker image inspect
• docker image ls or docker image ls --no-trunc
• docker history IMAGE

Docker Operation

• docker run IMAGE|IMAGE_ID : https://docs.docker.com/engine/reference/run/
• docker start CONTAINER_ID|CONTAINER_NAME: https://docs.docker.com/engine/reference/commandline/start/
• docker stop CONTAINER_ID|CONTAINER_NAME: https://docs.docker.com/engine/reference/commandline/stop/
• docker restart CONTAINER_ID|CONTAINER_NAME: https://docs.docker.com/engine/reference/commandline/restart/

Docker/cgroup Performance information

• systemd-cgtop

Docker Swarm

• docker swarm init
• docker swarm
• docker nodes
• docker node ls
• docker swarm join
• docker service create

Maintenance

• docker system prune -a remove unused and dangling images. Therefore any images being used in a container, whether they have been exited or currently running, will NOT be affected.. See also: docker system info

Docker Volumes

• docker volume create --name VOLUME_NAME
• docker volume ls: https://docs.docker.com/engine/reference/commandline/volume_ls/
• docker volume rm VOLUME_NAME
• docker volume: https://docs.docker.com/engine/reference/commandline/volume/
• docker volume inspect VOLUME: https://docs.docker.com/engine/reference/commandline/volume_inspect/

• docker inspect -f '{{ .Mounts }}' CONTAINER_NAME

• docker volumes prune
• docker system prune --volumes

Secrets

• docker secrets (Feb 2017) (swarm mode only)

Docker logging

Docker support logging to format or different platforms, such as, json-file, syslog, journald, gelf, fluentd, awslogs, splunk, etwlogs, gcplogs and logentries.

• Configuration is done at docker container start time with command docker run -it --log-drive LOG_METHOD CONTAINER_ID
• Check method configured in a running container:
  • docker inspect -f 'Template:.HostConfig.LogConfig.Type' CONTAINER_ID
  • docker inspect -f 'Template:.HostConfig.LogConfig' CONTAINER_ID
• View logs

docker logs CONTAINER_NAME_OR_ID (Docker Community Engine only support: local, json-file and journald)

docker logs CONTAINER_NAME_OR_ID 2>&1 | grep "STRING_TO_SEARCH" (You will need to redirect outputs to be able to grep output)

See https://docs.docker.com/config/containers/logging/ for more information

Misc

• docker tag

Activities

1. Read docker blog: https://blog.docker.com/
2. Read Docker Engine release notes (2017) and Docker CE or Docker EE releases.
3. Understand the difference between an image and a container, Docker Images vs. Containers: https://stackoverflow.com/a/26960888
4. Understand the difference between docker start and docker run: https://stackoverflow.com/questions/34782678/difference-between-running-and-starting-a-docker-container. See also runC
5. Read Stackoverflow questions related to docker: https://stackoverflow.com/questions/tagged/docker?tab=Votes
6. Read about Docker Image Manifest Version 2, Schema 2: https://github.com/docker/distribution/blob/fda42e5ef908bdba722d435ff1f330d40dfcd56c/docs/spec/manifest-v2-2.md

See also

• Docker: docker-compose, Docker Desktop, Docker Scout, Docker Swarm, Docker Volumes, Docker images management, docker network, docker inspect, docker volume inspect, Dockerfile, Docker Engine release notes,docker kill, moby, Docker-in-Docker, docker context, buildx, docker tag, docker system prune, Docker Hub, hub-tool, /etc/docker/daemon.json, hostconfig.json, dockerd, logs, Docker logging, Backup, docker service, depends on, --dns, --filter, --mount, docker login, docker build, apt remove docker.io, .dockerignore, docker context ls | docker-machine, .docker/, PWD, $HOME/.docker/config.json, Docker ID, --env-file, docker --help
• Docker Hub official Docker container image registry
• docker compose
• Jenkins X
• Elastic Container Service (ECS)
• AWS Elastic Container Registry (ECR)
• EKS, Kubernetes and Pods
• Container: runC
• Binary repository manager: JFrog Artifactory
• containerd
• KVM, multipass

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Source: https://en.wikiversity.org/wiki/DevOps/Docker