The Docker Quickstart Guide for Developers

This Docker Quickstart Guide for Developers aims to get developers familiar with Docker as quickly as possible.

Providing you with the knowledge to be able to use Docker in your personal and professional projects.

What is Docker?

Docker is a tool written in Golang that provides the ability to run applications within things called containers.

It removes the age-old “works on my machine” problems that plagued many software developers and testers lives.

Understanding the Terminology

Dockerfile: A file that lists what will be installed and available to use for later.

Image: A built Dockerfile located on a specific machine.

Container: A running instance of a built and deployable image. It is a standardized unit of software.

Registry: A location to store and share Docker configurations, images and containers.

Getting a Docker Hub Account

Docker Hub is the default place for where all Docker Registry URLs point.

It is free to get an account, additional features come with paid plans.

Register for an account at https://hub.docker.com/signup.

Installing Docker

To install Docker on your local machine or a server, go to the downloads section of the Docker website.

The Docker CLI should now be available in the command-line by typing docker and pressing Enter.

$ docker Usage: docker [OPTIONS] COMMAND A self-sufficient runtime for containers Options: --config string Location of client config files (default "/Users/ao/.docker") -c, --context string Name of the context to use to connect to the daemon (overrides DOCKER_HOST env var and default context set with "docker context use") -D, --debug Enable debug mode -H, --host list Daemon socket(s) to connect to -l, --log-level string Set the logging level ("debug"|"info"|"warn"|"error"|"fatal") (default "info") --tls Use TLS; implied by --tlsverify --tlscacert string Trust certs signed only by this CA (default "/Users/ao/.docker/ca.pem") --tlscert string Path to TLS certificate file (default "/Users/ao/.docker/cert.pem") --tlskey string Path to TLS key file (default "/Users/ao/.docker/key.pem") --tlsverify Use TLS and verify the remote -v, --version Print version information and quit Management Commands: builder Manage builds config Manage Docker configs container Manage containers context Manage contexts image Manage images network Manage networks node Manage Swarm nodes plugin Manage plugins secret Manage Docker secrets service Manage services stack Manage Docker stacks swarm Manage Swarm system Manage Docker trust Manage trust on Docker images volume Manage volumes Commands: attach Attach local standard input, output, and error streams to a running container build Build an image from a Dockerfile commit Create a new image from a container's changes cp Copy files/folders between a container and the local filesystem create Create a new container deploy Deploy a new stack or update an existing stack diff Inspect changes to files or directories on a container's filesystem events Get real time events from the server exec Run a command in a running container export Export a container's filesystem as a tar archive history Show the history of an image images List images import Import the contents from a tarball to create a filesystem image info Display system-wide information inspect Return low-level information on Docker objects kill Kill one or more running containers load Load an image from a tar archive or STDIN login Log in to a Docker registry logout Log out from a Docker registry logs Fetch the logs of a container pause Pause all processes within one or more containers port List port mappings or a specific mapping for the container ps List containers pull Pull an image or a repository from a registry push Push an image or a repository to a registry rename Rename a container restart Restart one or more containers rm Remove one or more containers rmi Remove one or more images run Run a command in a new container save Save one or more images to a tar archive (streamed to STDOUT by default) search Search the Docker Hub for images start Start one or more stopped containers stats Display a live stream of container(s) resource usage statistics stop Stop one or more running containers tag Create a tag TARGET_IMAGE that refers to SOURCE_IMAGE top Display the running processes of a container unpause Unpause all processes within one or more containers update Update configuration of one or more containers version Show the Docker version information wait Block until one or more containers stop, then print their exit codes Run 'docker COMMAND --help' for more information on a command.
Code language: Bash (bash)

Getting Started with Common Docker Commands

Running a Docker Container

Download, install and run the hello-world image to see how it all works.

docker run hello-world :: if this is the first time you should be able to see the message :: Unable to find image 'hello-world:latest' locally :: latest: Pulling from library/hello-world :: 1b930d010525: Pull complete :: Digest: sha256:4fe721ccc2e8dc7362278a29dc660d833570ec2682f4e4194f4ee23e415e1064 :: 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/
Code language: Bash (bash)

Running in Interactive Mode / Bash

docker run -it ubuntu bash
Code language: Bash (bash)

See all running images

You can use docker ps to view all currently running images.

docker ps :: CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
Code language: Bash (bash)

You can also see all the images that have run previously.

docker ps -a :: CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS :: NAMES :: 4a76281f9c53 hello-world "/hello" 2 minutes ago Exited (0) 2 minutes ago :: happy_poincare :: the name part is generated automatically so it probably will be different for you
Code language: Bash (bash)

Remove images

Remove our previously generated image

docker rm happy_poincare
Code language: Bash (bash)

Test if it was really deleted.

docker ps -a :: CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
Code language: Bash (bash)

Run with custom names

specify a custom name for the container

docker run --name test_container hello-world :: 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/
Code language: Bash (bash)

See it in action

docker ps -a :: CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES :: d345fe1a4f41 hello-world "/hello" About a minute ago Exited (0) About a minute ago test_container
Code language: Bash (bash)

as you can see the name is now what we have specified

Retrieve logs

Retrieve logs from a named container

docker logs test_container :: 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/
Code language: Bash (bash)

Mount and work with Volumes

Docker provides the ability to share the local filesystem with the filesystem in the running container.

docker run -d --name image-name -v /path/to/app/directory/on/host:/var/www/on/container ubuntu:latest
Code language: Bash (bash)

Now all files changes made locally will be available directly within the running container.

Alternatively, you can specify the mount volume from your actual Dockerfile:

FROM alpine VOLUME ["/data"] ENTRYPOINT ["/bin/sh"]
Code language: Dockerfile (dockerfile)

Create an actual volume with docker volume create volume_name.

See what volumes exist with docker volume ls.

Remove a volume with docker volume rm volume_name.

If you don’t want the container to be able to write to the volume, you can mount it in read-only mode by appending a :ro to the container mount location:

docker run -d --name image-name -v /path/to/app/directory/on/host:/var/www/on/container:ro ubuntu:latest
Code language: Bash (bash)

Commit changes from a Throwaway Container

Run your normal docker build process:

docker build -t image-name .
Code language: Bash (bash)

Now run a command in a throwaway container that uses volumes and make any changes:

docker run -v /some:/volume --name temp-container image-name /some/post-configure/command
Code language: Bash (bash)

Replace the original image with the result of the changed container:

(reverting CMD to whatever it was, otherwise it will be set to /some/post-configure/command)

docker commit --change="CMD bash" temp-container image-name
Code language: Bash (bash)

Finally, delete the temporary container:

docker rm temp-container
Code language: Bash (bash)

Run an Ubuntu container

docker run ubuntu :: Unable to find image 'ubuntu:latest' locally :: latest: Pulling from library/ubuntu :: 2746a4a261c9: Pull complete :: 4c1d20cdee96: Pull complete 0d3160e1d0de: Pull complete c8e37668deea: Pull complete Digest: sha256:250cc6f3f3ffc5cdaa9d8f4946ac79821aafb4d3afc93928f0de9336eba21aa4 :: Status: Downloaded newer image for ubuntu:latest
Code language: Bash (bash)

Run our new Ubuntu container in interactive mode through Bash.

docker run -it ubuntu :: [email protected]:/# uname :: Linux
Code language: Bash (bash)

How to write a simple Dockerfile

Create a file called index.html and insert the following code:

<h1>Hello world!</h1>
Code language: HTML, XML (xml)

Create a file called Dockerfile and insert the following code:

FROM busybox ADD app/index.html /www/index.html EXPOSE 8005 CMD httpd -p 8005 -h /www; tail -f /dev/null
Code language: Dockerfile (dockerfile)

Now in the command-line, run docker build -t hello-world-demo ..

This tells Docker to build an image which we will call hello-world-demo and to use the Dockerfile located in the current directory to do so (because of the dot, which means ‘local directory’).

Now we can run our newly created image by saying docker run -p 80:8005 hello-world-demo.

This looks for a locally found Docker image called hello-world-demo and runs it. It also port maps our local port 80 to the container’s port 8005, which we exposed in our Dockerfile to show the index.html file through the httpd utility.

Push our Docker image to Docker Hub

It’s great to be able to create images and use them locally, but more often than not, you will want to share them with your colleagues or the greater community. Or perhaps you will store them to run on servers somewhere.

To do this, you will first need to login to Docker from the command-line. This is easy and can be done by running docker login.

Once this is done, we will tag our image to a particular repository on our Docker Hub account.

To do this, type docker tag hello-world-demo {your_dockerhub_user}/hello-world-demo.

Then finally, push it to a specific tag, or the latest tag.

This can be done by typing docker push {your_dockerhub_user}/hello-world-demo:latest.

Final Thoughts

Docker is a fantastic invention and very useful tool that every developer should make use of wherever needed.

With the above few lessons learned, it should now be possible to start using Docker in your day to day development work.

For more on using the Docker CLI, check out Use the Docker Command-Line on the Docker Documentation site.

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