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 <a href="https://github.com/docker/cli" target="_blank" rel="noreferrer noopener nofollow">Docker CLI</a> 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.
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/
Running in Interactive Mode / Bash
docker run -it ubuntu 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
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
Remove images
Remove our previously generated image
docker rm happy_poincare
Test if it was really deleted.
docker ps -a
:: CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
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/
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
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/
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
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"]
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
Commit changes from a Throwaway Container
Run your normal docker build process:
docker build -t image-name .
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
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
Finally, delete the temporary container:
docker rm temp-container
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
Run our new Ubuntu container in interactive mode through Bash.
docker run -it ubuntu
:: root@e2cac48323d2:/# uname
:: Linux
How to write a simple Dockerfile
Create a file called index.html and insert the following code:
<h1>Hello world!</h1>
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
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.