Welcome to our comprehensive guide on Docker, the revolutionary containerization platform that has taken the world of software development by storm. If you’re looking to gain an edge in today’s competitive digital landscape, mastering Docker is a must. In this article, we’ll provide you with an in-depth Docker cheat sheet that covers everything you need to know to get started and stay ahead of the competition. So, let’s dive in!
What is Docker?
Docker is an open-source platform that allows developers to automate applications’ deployment, scaling, and management in lightweight, portable containers. Containers are isolated environments that contain everything needed to run a piece of software, including the code, runtime, system tools, and libraries. Unlike traditional virtualization, which emulates an entire operating system, Docker containers share the host system’s kernel, making them lightweight, fast, and efficient.
Why Docker is a Game Changer
Docker has revolutionized the way software is developed, deployed, and managed. Here are some key reasons why Docker is a game changer in the world of software development:
Portability: Docker containers are self-sufficient and can run on any system that supports Docker, regardless of the underlying infrastructure. This makes it easy to deploy applications across different environments, such as development, testing, and production, without worrying about compatibility issues.
Scalability: Docker enables horizontal scaling, allowing applications to be seamlessly scaled up or down based on demand. This makes it ideal for modern, cloud-native applications that handle variable workloads efficiently.
Consistency: Docker containers encapsulate the entire application stack, including the code, runtime, and dependencies. This ensures that applications run consistently across different environments, eliminating the dreaded “it works on my machine” problem.
Speed: Docker allows for rapid deployment and testing of applications, making it ideal for agile development workflows. Containers can be spun up in seconds, enabling quick iteration and faster time to market.
Security: Docker provides built-in isolation between containers, making it harder for malicious code to escape and compromise the host system. Containers can also be configured with fine-grained security settings, making them more secure than traditional monolithic applications.
Docker Basics: Getting Started
Now that you have a basic understanding of what Docker is and why it’s a game changer, let’s dive into the fundamentals of Docker. Here are the essential Docker commands and concepts you need to know to get started:
Docker CLI
Manage images
docker build
docker build [options] .
-t "app/container_name" # name
Create an image from a Dockerfile.
docker run
docker run [options] IMAGE
# see `docker create` for options
Run a command in an image.
Manage containers
docker create
docker create [options] IMAGE
-a, --attach # attach stdout/err
-i, --interactive # attach stdin (interactive)
-t, --tty # pseudo-tty
--name NAME # name your image
-p, --publish 5000:5000 # port map
--expose 5432 # expose a port to linked containers
-P, --publish-all # publish all ports
--link container:alias # linking
-v, --volume `pwd`:/app # mount (absolute paths needed)
-e, --env NAME=hello # env vars
Example
$ docker create --name app_redis_1 \
--expose 6379 \
redis:3.0.2
Create a container from an image.
docker exec
docker exec [options] CONTAINER COMMAND
-d, --detach # run in background
-i, --interactive # stdin
-t, --tty # interactive
Example
$ docker exec app_web_1 tail logs/development.log
$ docker exec -t -i app_web_1 rails c
Run commands in a container.
docker start
docker start [options] CONTAINER
-a, --attach # attach stdout/err
-i, --interactive # attach stdin
docker stop [options] CONTAINER
Start/stop a container.
docker ps
$ docker ps
$ docker ps -a
$ docker kill $ID
Manage containers using ps/kill.
Images
docker images
$ docker images
REPOSITORY TAG ID
ubuntu 12.10 b750fe78269d
me/myapp latest 7b2431a8d968
$ docker images -a # also show intermediate
Manages images.
docker rmi
docker rmi b750fe78269d
Deletes images.
Also, see
- Getting Started (docker.io)
Dockerfile
Inheritance
FROM ruby:2.2.2
Variables
ENV APP_HOME /myapp
RUN mkdir $APP_HOME
Initialization
RUN bundle install
WORKDIR /myapp
VOLUME ["/data"]
# Specification for mount point
ADD file.xyz /file.xyz
COPY --chown=user:group host_file.xyz /path/container_file.xyz
Onbuild
ONBUILD RUN bundle install
# when used with another file
Commands
EXPOSE 5900
CMD ["bundle", "exec", "rails", "server"]
Entrypoint
ENTRYPOINT ["executable", "param1", "param2"]
ENTRYPOINT command param1 param2
Configures a container that will run as an executable.
ENTRYPOINT exec top -b
This will use shell processing to substitute shell variables and will ignore any CMD or docker run command line arguments.
Metadata
LABEL version="1.0"
LABEL "com.example.vendor"="ACME Incorporated"
LABEL com.example.label-with-value="foo"
LABEL description="This text illustrates \
that label-values can span multiple lines."
See also
docker-compose
Basic example
# docker-compose.yml
version: '2'
services:
web:
build: .
# build from Dockerfile
context: ./Path
dockerfile: Dockerfile
ports:
- "5000:5000"
volumes:
- .:/code
redis:
image: redis
Commands
docker-compose start
docker-compose stop
docker-compose pause
docker-compose unpause
docker-compose ps
docker-compose up
docker-compose down
Reference
Building
web:
# build from Dockerfile
build: .
# build from custom Dockerfile
build:
context: ./dir
dockerfile: Dockerfile.dev
# build from image
image: ubuntu
image: ubuntu:14.04
image: tutum/influxdb
image: example-registry:4000/postgresql
image: a4bc65fd
Ports
ports:
- "3000"
- "8000:80" # guest:host
# expose ports to linked services (not to host)
expose: ["3000"]
Commands
# command to execute
command: bundle exec thin -p 3000
command: [bundle, exec, thin, -p, 3000]
# override the entrypoint
entrypoint: /app/start.sh
entrypoint: [php, -d, vendor/bin/phpunit]
Environment variables
# environment vars
environment:
RACK_ENV: development
environment:
- RACK_ENV=development
# environment vars from file
env_file: .env
env_file: [.env, .development.env]
Dependencies
# makes the `db` service available as the hostname `database`
# (implies depends_on)
links:
- db:database
- redis
# make sure `db` is alive before starting
depends_on:
- db
Other options
# make this service extend another
extends:
file: common.yml # optional
service: webapp
volumes:
- /var/lib/mysql
- ./_data:/var/lib/mysql
Advanced features
Labels
services:
web:
labels:
com.example.description: "Accounting web app"
DNS servers
services:
web:
dns: 8.8.8.8
dns:
- 8.8.8.8
- 8.8.4.4
Devices
services:
web:
devices:
- "/dev/ttyUSB0:/dev/ttyUSB0"
External links
services:
web:
external_links:
- redis_1
- project_db_1:mysql
Hosts
services:
web:
extra_hosts:
- "somehost:192.168.1.100"
services
To view the list of all the services running in the swarm
docker service ls
To see all running services
docker stack services stack_name
to see all services logs
docker service logs stack_name service_name
To scale services quickly across qualified node
docker service scale stack_name_service_name=replicas
clean up
To clean or prune unused (dangling) images
docker image prune
To remove all images which are not in use containers, add – a
docker image prune -a
To prune your entire system
docker system prune
To leave swarm
docker swarm leave
To remove swarm ( deletes all volume data and database info)
docker stack rm stack_name
To kill all running containers
docker kill $(docekr ps -q )