Getting started with Docker + Cheat Sheet

Docker is a containerization platform that allows developers to easily create, deploy, and run applications in a lightweight and portable environment. Docker containers are similar to virtual machines, but they are much more lightweight and efficient. With Docker, developers can package their applications and all the necessary dependencies into a single container that can be run on any platform.

The history of Docker dates back to 2010 when the founder, Solomon Hykes, created a prototype tool that would eventually become Docker. Originally called dotCloud, Docker was created as an internal tool for dotCloud's Platform as a Service (PaaS) product.

In 2013, Docker was released as an open-source project, and it quickly gained popularity in the developer community. Docker's containerization technology was seen as a major improvement over traditional virtual machines, providing a more lightweight and efficient way to package and deploy applications.

In 2014, Docker Inc. was founded to commercialize Docker and provide enterprise-level support and services. Docker continued to grow in popularity and became a dominant force in the containerization space, with a large and active community of developers and users.

In 2016, Docker introduced Docker Swarm, a container orchestration tool that allows users to manage and scale Docker containers across multiple hosts. This was followed by the release of Docker Enterprise, a commercial version of Docker that includes additional features and support for enterprise-level deployments.

Since its release, Docker has become a critical tool for modern software development and deployment. It has enabled developers to create and deploy applications more efficiently and with greater flexibility, and has helped to drive the adoption of containerization across the industry.

Use Cases

Docker is ideal for a wide range of use cases, including:

Application development and testing

Developers can use Docker to build and test their applications in a consistent and reproducible environment.

Microservices

Docker allows developers to break down their applications into smaller, independent services that can be deployed and managed separately.

Continuous Integration/Continuous Deployment (CI/CD)

Docker is often used in CI/CD pipelines to create a consistent environment for testing and deploying applications.

Hybrid cloud

Docker containers can be easily moved between on-premises and cloud environments, making it an ideal platform for hybrid cloud deployments.

Docker Advantages Compared to Traditional Server Setups

There are several advantages to using Docker compared to traditional server setups:

Portability

Docker containers can be run on any platform that supports Docker, making it easy to move applications between different environments.

Efficiency

Docker containers are lightweight and efficient, allowing developers to run more containers on the same hardware than they would be able to with virtual machines.

Consistency

Docker provides a consistent environment for applications, ensuring that they will run the same way on any platform.

Isolation

Docker containers provide a high degree of isolation between applications, reducing the risk of conflicts and security issues.

Scalability

Docker makes it easy to scale applications horizontally by adding more containers to a cluster.

Docker vs. Virtual Machines (VMs)

Docker and VMs are both used for running applications, but they have different architectures and use cases.

A virtual machine is a software emulation of a physical machine. It creates a separate operating system environment within a host operating system. Each VM runs its own operating system and has access to virtualized hardware resources, such as CPU, memory, and storage. Applications and dependencies can be installed within the VM just like a physical machine. This architecture provides a high degree of isolation and security, but also has higher resource requirements because each VM requires its own copy of an operating system and must allocate hardware resources separately.

Docker, on the other hand, uses containerization to run applications. Containers are lightweight and portable, and they share the kernel of the host operating system. Each container runs a single process or a set of processes that are isolated from other containers and the host system. Containers can be easily created, started, stopped, and moved between different hosts. Docker images can be used to package applications and their dependencies in a container, which makes it easy to create a consistent and reproducible environment for running the application.

One of the key differences between Docker and virtual machines is the level of isolation they provide. Virtual machines provide a high degree of isolation, while Docker containers provide a more lightweight and efficient form of isolation. Docker containers also have lower resource requirements, as they share the kernel of the host operating system and do not require their own copy of an operating system.

In terms of use cases, virtual machines are typically used for running applications that require a high level of isolation or security, or for running legacy applications that cannot be easily ported to a containerized environment. Docker is ideal for running modern microservices-based applications, as it provides a lightweight and portable way to package and deploy these applications.

Overall, Docker and virtual machines are complementary technologies that can be used together to provide a flexible and scalable infrastructure for running applications. The choice between Docker and virtual machines depends on the specific use case and requirements of the application.

Installing Docker

To install Docker, follow these steps:

Go to the Docker website and download the appropriate version of Docker for your platform.
Follow the installation instructions for your platform.
Once Docker is installed, open a terminal or command prompt and run the following command to verify that Docker is installed correctly:

docker --version

Dockerfile

A Dockerfile is a text file that contains instructions for building a Docker image. Here is an example Dockerfile:

# Use an official Python runtime as a parent image
FROM python:3.8-slim-buster

# Set the working directory to /app
WORKDIR /app

# Copy the current directory contents into the container at /app
COPY . /app

# Install any needed packages specified in requirements.txt
RUN pip install --trusted-host pypi.python.org -r requirements.txt

# Make port 80 available to the world outside this container
EXPOSE 80

# Define environment variable
ENV NAME World

# Run app.py when the container launches
CMD ["python", "app.py"]

This Dockerfile starts with an official Python runtime image, sets the working directory, copies the contents of the current directory into the container, installs any necessary packages, exposes port 80, sets an environment variable, and specifies the command to run when the container is launched.

Docker Compose

Docker Compose is a tool that allows you to define and run multi-container Docker applications. Here is an example docker-compose.yml file:

version: "3"
services:
  web:
    build: .
    ports:
      - "5000:5000"
    volumes:
      - .:/code
    depends_on:
      - redis
  redis:
    image: "redis:alpine"

This `docker-compose.ymlfile defines two services:webandredis. The webservice is built from the current directory, maps port 5000 to the host, mounts the current directory as a volume, and depends on theredisservice. Theredisservice uses theredis:alpine` image.

To run a Docker Compose application, navigate to the directory containing the docker-compose.yml file and run the following command:

docker-compose up

This command will start all the services defined in the docker-compose.yml file.

Docker Cheat Sheet

docker build

Builds an image from a Dockerfile.

docker run

Runs a container from an image.

docker ps / docker container list

Lists running containers.

docker ps -a / docker container list -a

Lists all containers (including stopped ones).

docker stop

Stops a running container.

docker rm

Removes one or more containers.

docker images

Lists available images.

docker rmi

Removes one or more images.

docker pull

Pulls an image from a registry.

docker push

Pushes an image to a registry.

docker-compose up

Starts a Docker Compose application.

docker exec -it <container name> /bin/bash

Opens a bash shell inside a running container. The -it options tell Docker to allocate a pseudo-TTY and to keep STDIN open even if not attached. The /bin/bash argument specifies the command to run inside the container.

docker inspect <container name>

Displays detailed information about a container.

docker top <container name>

Displays the running processes inside a container.

docker network ls

List Docker networks

docker network inspect <network name>

Displays detailed information about a network.

More: Docker Official Cheat Sheet (PDF)

What are the weaknesses and disadvantages of Docker?

While Docker has many advantages, it also has some disadvantages that should be considered. Here are some of the main disadvantages of Docker:

Complexity

Docker can be complex to set up and configure, particularly for more advanced use cases such as orchestration and scaling. There is a steep learning curve for new users, and mistakes in configuration can lead to security issues and other problems.

Security

Docker introduces new security concerns, as containers share the same kernel as the host system and can potentially access sensitive data or resources. Proper configuration and isolation are critical for maintaining the security of a Docker environment.

Resource Overhead

While Docker containers are more lightweight than virtual machines, they still require additional resources to run compared to running an application natively on the host system. This can be a concern for applications with strict resource requirements.

Compatibility Issues

Docker images may not always be compatible across different platforms and architectures, and different versions of Docker may have different behavior or features. This can lead to compatibility issues and require additional effort to maintain consistency across different environments.

Persistence

By default, Docker containers are designed to be ephemeral and disposable, which can make it challenging to maintain persistence across container restarts or upgrades. Proper data management and backup strategies are critical for maintaining data integrity.

It's important to keep in mind that many of these disadvantages can be mitigated through proper configuration, best practices, and the use of complementary tools and services. Docker remains a powerful and widely used containerization platform, but it's important to understand and address its limitations and challenges.

Docker Best Practices

There are several best practices for using Docker that can help ensure that your containers are secure, efficient, and well-managed. Here are some of the most important Docker best practices:

Use official images

Whenever possible, use official Docker images rather than building your own. Official images are maintained by the Docker community and are regularly updated to ensure security and stability.

Minimize the size of your images

Keep your images as small as possible by removing unnecessary files and dependencies. Smaller images are faster to download and use less storage space.

Run as non-root user

Running containers as a non-root user can improve security by reducing the risk of privilege escalation attacks.

Use Docker Compose

Use Docker Compose to define and manage multi-container applications. Docker Compose provides an easy way to manage the configuration and deployment of multiple containers.

Mount volumes for persistent data

Mount volumes rather than using container storage for persistent data. This makes it easier to manage data across containers and ensures that data is not lost if a container is removed.

Use environment variables

Use environment variables to pass configuration information to containers. This makes it easier to manage container configuration across different environments.

Monitor your containers

Use tools such as Docker stats or cAdvisor to monitor container resource usage and performance. This can help you identify performance issues and optimize container resource usage.

Secure your containers

Implement security best practices, such as limiting container permissions, securing network connections, and using secure images and repositories.

Automate container builds and deployments

Use automation tools such as Dockerfiles, CI/CD pipelines, and infrastructure-as-code tools to automate container builds and deployments. This can improve efficiency and reduce errors.

Keep Docker and images up to data

Keep your Docker version and images up to date to ensure that you have the latest security patches and bug fixes.

Following these best practices can help ensure that your Docker containers are secure, efficient, and well-managed.

What are the alternatives to Docker?

There are several alternatives to Docker in the containerization space. Here are a few:

Podman

Podman is a tool that provides a similar interface to Docker but doesn't require a daemon to run. It uses the same container image format as Docker and can run Docker images, making it an easy alternative for those already familiar with Docker.
https://podman.io/

LXC/LXD

LXC (Linux Containers) is a containerization technology that predates Docker. It provides a more low-level interface for managing containers than Docker but requires more manual configuration. LXD is a higher-level tool built on top of LXC that provides a more user-friendly interface.
https://linuxcontainers.org/

rkt

rkt is a containerization engine developed by CoreOS. It uses a different container image format than Docker but can run Docker images. It focuses on security and isolation and provides a simpler and more modular architecture than Docker.
https://coreos.com/rkt/

Kubernetes

Kubernetes is an open-source container orchestration platform that can run containers from various containerization engines, including Docker. It provides a powerful platform for managing containerized applications at scale and is widely used in production environments.
https://kubernetes.io/

OpenShift

OpenShift is a container application platform that builds on top of Kubernetes. It provides a comprehensive set of tools for building, deploying, and managing containerized applications and is designed for use in enterprise environments.
https://www.openshift.com/

Each of these alternatives has its own strengths and weaknesses, and the choice of which one to use depends on the specific use case and requirements of the application. However, Docker remains the most widely used containerization platform and has a large ecosystem of tools and services built around it.

Conclusion

Docker is a powerful containerization platform that provides many benefits over traditional server setups. It allows developers to easily create, deploy, and run applications in a lightweight and portable environment. Docker containers are similar to virtual machines, but they are much more lightweight and efficient. With Docker, developers can package their applications and all the necessary dependencies into a single container that can be run on any platform.

While Docker has many advantages, it also has some disadvantages that should be considered, such as complexity, security, resource overhead, compatibility issues, and persistence. However, many of these disadvantages can be mitigated through proper configuration, best practices, and the use of complementary tools and services.

Overall, Docker is a popular and widely used containerization platform that provides a flexible and scalable infrastructure for running applications. Its popularity and large ecosystem of tools and services make it a great choice for modern application development and deployment.

Updated March 11, 2023