Docker Notes

1. What is Docker

  • Docker is a container platform for developers and sysadmins to build, run, and share applications with containers.

  • It runs in the cloud via a cloud provider or on laptops and data centers VMs.

  • It is used to containerize legacy apps.

  • It is used to build new microservices apps.

2. Containerization Features

List of Containerization Features:
Flexible

Even the most complex applications can be containerized.

Lightweight

Containers leverage and share the host kernel, making them much more efficient in terms of system resources than virtual machines. It runs a discrete process, taking no more memory than any other executable, making it lightweight.

Portable

You can build locally, deploy to the cloud, and run anywhere.

Loosely coupled

Containers are highly self-sufficient and encapsulated, allowing you to replace or upgrade one without disrupting others.

Self Contained

Guarantees that applications will always run the same regardless of where they are deployed.

Scalable

You can increase and automatically distribute container replicas across a datacenter.

Secure

Containers apply aggressive constraints and isolations to processes without any configuration required on the part of the user.

Isolation

Each container interacts with its own private filesystem provided by a Docker image. An image includes everything needed to run an application - the code or binary, runtimes, dependencies, and any other filesystem objects required.

The following is a graphical representation of several containers hosted by Docker and their relationship to the host system:

containers-diagram

3. Docker Image

  • An image includes everything needed to run an application in a container - the code or binary runtimes, dependencies, and any other required filesystem objects.

  • It also contains other configuration for the container, such as environment variables, a default command to run, and other metadata.

  • An image can be used to instantiate multiple container instances.

4. Docker Hub

It is the world’s largest repository of container images with an array of content sources including container community developers, open source projects and independent software vendors (ISV) building and distributing their code in containers.

— Docker

  • Docker Hub is a repository service provided by Docker for finding and sharing container images with your team.

  • You can search the Docker Hub repository from here.

5. Docker Engine

  • Allows you to build, run, and share containerized applications on Linux/Windows/Macs.

5.1. Install Docker Engine

5.1.1. Windows Desktop

5.1.2. Windows Server

TBA

6. Docker File

  • This file must be named Dockerfile. It describes the build process for creating an image.

  • It contains necessary commands for building an image and running the application.

6.1. Docker File Commands

A full reference can be found here
List of Docker File Commands:
ADD

TBA

COPY

TBA

ENV

TBA

EXPOSE

TBA

FROM

TBA

LABEL

TBA

STOPSIGNAL

TBA

USER

TBA

VOLUME

TBA

WORKDIR

TBA

7. Docker Version Commands

7.1. Version

  • Shows docker version:

    docker --version

Docker version 20.10.5, build 55c4c88

8. Docker Image Commands

8.1. pull

  • Download an image:

    docker pull <image name>

8.2. image ls

  • List all downloaded images:

    docker image ls

REPOSITORY                     TAG          IMAGE ID       CREATED       SIZE
wordpress                      latest       c01290f258b3   4 days ago    550MB
camunda/camunda-bpm-platform   run-latest   c1b49a5b4227   11 days ago   243MB
stonebranch/universal-agent    latest       eca81e31c6a3   12 days ago   1.53GB
busybox                        latest       388056c9a683   12 days ago   1.23MB
docker/getting-started         latest       3ba8f2ff0727   4 weeks ago   27.9MB

8.3. image history

  • History of a docker image:

    docker image history <image name>

8.4. image rm

  • Removes a docker image that is referenced by its Image ID:

    sudo docker image rm <image ID>

8.5. image prune

  • Prune will remove all dangling images and any unused images that are not referenced by any running or stopped containers

    Command
    sudo docker image prune -a
    Example
    sudo docker image prune -a
WARNING! This will remove all images without at least one container associated to them.
Are you sure you want to continue? [y/N] y
Deleted Images:
untagged: docker.repo.xackleystudio.com/com-xs-spa-accounting@sha256:0260a30a67ad213f3fb8e24a11d5fdcc65f5d3ca43fd2221b8a13c6aa31f86b7
deleted: sha256:5b1805a2051a89e5c372e6062f301160e65c085220b2fe56bb6d4fc5733f174b
deleted: sha256:d7abd446fefb3853b30657882d81572a4ed157b53a5d6de2288b439cb64098d7
untagged: docker.repo.xackleystudio.com/com-xs-spa-accounting@sha256:353148f8ca972224d21c589dd030f7cc18bd7da941e4b49ef2da62d24732e867
deleted: sha256:fed35a7838e85cf02163b0e70872828e3b279c63b93a0a1e589f10927efb7647
deleted: sha256:07ca8a1e9a6e1bcb9f5afe9b5b191717381121f54fe720f53729d989b57072bf

Total reclaimed space: 71.41MB

8.6. system prune

  • Delete all stopped containers and delete all images in the build cache:

    docker system prune
WARNING! This will remove:
  - all stopped containers
  - all networks not used by at least one container
  - all dangling images
  - all dangling build cache

Are you sure you want to continue? [y/N] y
Deleted Containers:
a06c836c2a2eb0c02084bdef480eb936cb396d669d5274dfb3f7af079bf75159
70e0b00f8a13aa75e76b3914c4677fac6d510229d1aeadd7297e97600d340056

Deleted build cache objects:
lq8fii44gmb83elngpz08rqyu
43cawslfsqbweb2ls6moacppd
56virr3nlkfplfunck4hbs8pr
a3k8smfqg80xk70v768stmogs
5v3cypmqiray0o4ny9wyfx7f3

Total reclaimed space: 400.5MB

9. Docker Lifecycle Commands

9.1. create

  • Instantiate a container from an image:

    docker create hello-world

70e0b00f8a13aa75e76b3914c4677fac6d510229d1aeadd7297e97600d340056

docker ps --all
CONTAINER ID   IMAGE         COMMAND    CREATED          STATUS    PORTS     NAMES
70e0b00f8a13   hello-world   "/hello"   33 seconds ago   Created             zen_bartik

9.2. start

  • Starts an already instantiated container by running the container’s startup command.

    docker start -a 70e0b00f8a13aa75e76b3914c4677fac6d510229d1aeadd7297e97600d340056

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

docker ps --all
CONTAINER ID   IMAGE         COMMAND    CREATED         STATUS                     PORTS     NAMES
70e0b00f8a13   hello-world   "/hello"   2 minutes ago   Exited (0) 2 minutes ago             zen_bartik

9.3. run

  • This command is a combination of the create and start commands:

    docker run -t -d hello-world                      (1)
Unable to find image 'hello-world:latest' locally (2)
latest: Pulling from library/hello-world          (3)
2db29710123e: Pull complete
Digest: sha256:507ecde44b8eb741278274653120c2bf793b174c06ff4eaa672b713b3263477b
Status: Downloaded newer image for hello-world:latest
ccd3e66e756adbebed35e0d6c8f821eb784537c55db67c40750092d028c468ac

docker ps --all (4)
CONTAINER ID   IMAGE         COMMAND    CREATED         STATUS                     PORTS     NAMES
ccd3e66e756a   hello-world   "/hello"   5 seconds ago   Exited (0) 4 seconds ago             friendly_yonath   (5)

docker run -t -d --name MyHelloWorld hello-world (6)
d2f9a1302796c264da5d80544e83b5e626aa7a60f93ec5b950408df39d087ae6

docker ps --all (7)
CONTAINER ID   IMAGE         COMMAND    CREATED          STATUS                      PORTS     NAMES
d2f9a1302796   hello-world   "/hello"   7 seconds ago    Exited (0) 5 seconds ago              MyHelloWorld    (8)
ccd3e66e756a   hello-world   "/hello"   49 seconds ago   Exited (0) 48 seconds ago             friendly_yonath (9)
    1 Instantiate a container based on the hello-world docker image.
    2 Docker image is not in the local Docker cache.
    3 Download the Docker image via the internet.
    4 List containers.
    5 Here’s the instantiated container with a randomly assigned name.
    6 Again, instantiate a container based on the hello-world docker image but name the container MyHelloWorld.
    7 List containers.
    8 The recently created docker image with the provided name of MyHelloWorld.
    9 The initial docker image with a randomly assigned name.

9.4. stop

  • Gracefully shutdown a container by name. The container is allowed a max of 10 seconds for a graceful shutdown. If it needs more than 10 seconds, a kill will be executed:

    docker ps (1)
CONTAINER ID   IMAGE     COMMAND            CREATED         STATUS         PORTS     NAMES
2d23f4790668   busybox   "ping google.com"  2 minutes ago   Up 2 minutes             cranky_elgamal (2)

docker stop cranky_elgamal (3)
cranky_elgamal

docker ps (4)
CONTAINER ID   IMAGE     COMMAND   CREATED   STATUS    PORTS     NAMES
    1 Get a listing of running containers.
    2 The name of this container is cranky_elgamal.
    3 Stop the container named cranky_elgamal.
    4 The container is no longer running.

9.5. kill

  • Immediately shutdown a container via its name:

    docker ps
CONTAINER ID   IMAGE     COMMAND            CREATED         STATUS         PORTS     NAMES
7d968dee18b5   busybox   "ping google.com"   3 seconds ago   Up 3 seconds             crazy_lehmann (1)

docker kill crazy_lehmann
crazy_lehmann

docker ps
CONTAINER ID   IMAGE     COMMAND   CREATED   STATUS    PORTS     NAMES
    1 The name of this container is crazy_lehmann

9.6. exec

  • Execute a command inside a container. In this example will interactively run the bash command which will give us shell access within the ubuntu container:

    docker run -dt ubuntu (1)
541e05be7d9c259ce443f91705c0064daaeb52ebfcfc9ea7826a4bbadbde32e5

docker ps (2)
CONTAINER ID   IMAGE     COMMAND       CREATED         STATUS         PORTS     NAMES
541e05be7d9c   ubuntu    "/bin/bash"   5 seconds ago   Up 4 seconds             distracted_hopper (3)

docker exec -it 541e05be7d9c bash (4)
root@541e05be7d9c:/# whoami       (5)
root                              (6)

root@541e05be7d9c:/# uname -a (7)
Linux 541e05be7d9c 5.4.72-microsoft-standard-WSL2 #1 SMP Wed Oct 28 23:40:43 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux (8)

root@541e05be7d9c:/#
    1 Start a detached instance of an ubuntu docker image.
    2 View running containers.
    3 The ubuntu container has an ID of 541e05be7d9c.
    4 Start a bash shell in the ubuntu container.
    5 Run the whomami command inside the container.
    6 The whoami command responds with root.
    7 Now we’ll run the uname -a command.
    8 The results of the uname -a command.

9.7. rm

  • Shuts down the container and deletes it:

    docker rm --force <container ID>

10. Docker Status commands

10.1. ps

List currently running docker images and related containers:

docker ps

CONTAINER ID   IMAGE                                COMMAND             CREATED              STATUS              PORTS                NAMES
f65fb9bcd3ec   stonebranch/universal-agent:latest   "./ua_entrypoint"   About a minute ago   Up About a minute   7878/tcp, 7887/tcp   My-UAG1

10.2. ps --all

List all docker images and related containers:

docker ps --all

CONTAINER ID   IMAGE                                COMMAND             CREATED         STATUS         PORTS                NAMES
f65fb9bcd3ec   stonebranch/universal-agent:latest   "./ua_entrypoint"   3 minutes ago   Up 3 minutes   7878/tcp, 7887/tcp   My-UAG1

10.3. stats

Show container memory/CPU usage in real-time:

docker stats

CONTAINER ID   NAME      CPU %     MEM USAGE / LIMIT     MEM %     NET I/O           BLOCK I/O   PIDS
f65fb9bcd3ec   My-UAG1   0.58%     20.34MiB / 12.42GiB   0.16%     5.08kB / 4.86kB   0B / 0B     22

10.4. logs

Get the log files from a running container:

docker logs -f busybox

11. Docker Cleanup Commands

11.1. system prune

This will remove unused images and folder in the /var/lib/docker/overlay2 directory.

sudo docker system prune -a -f
Example
mattosd@v-Ubuntu00:~$ sudo docker system prune -a -f
[sudo] password for mattosd:
Deleted Networks:
docker-compose_default
docker-devops-stack_default

Deleted Images:
untagged: ubuntu:latest
untagged: ubuntu@sha256:34fea4f31bf187bc915536831fd0afc9d214755bf700b5cdb1336c82516d154e
deleted: sha256:df5de72bdb3b711aba4eca685b1f42c722cc8a1837ed3fbd548a9282af2d836d
deleted: sha256:629d9dbab5edeac7fa51f205839d7f9bb629a5e83548da3a183fb66c22fe7af7

Total reclaimed space: 77.83MB

12. Docker Container Examples

  • This section will guide you through downloading various public Docker images and launching them as containers.

  • An installed and configured Docker Engine / Podman will be required in order to execute the examples.

12.1. Docker - Getting Started

Click here for the Getting Started document.

12.2. Ubuntu

Click here for the Ubuntu document.

12.3. WordPress

Click here for the WordPress document.

12.4. GitLab

Click here for the GitLab document.

12.5. Camunda

Click here for the Camunda document.

12.6. Universal Automation Center Agent (UAC)

Click here for the UAC document.

12.7. Portainer

Click here for the Portainer document.

12.8. Reverse Proxy

  • is this a thing or can this be accomplished with Apache?

12.9. Mail Server

12.10. Password Manager

  • Maybe Bitwarden?

13. Docker Stack Examples

These are not really Docker Stacks - it’s Docker Compose at the moment

13.1. DevOps

Click here for the DevOps document.