What is called Docker?

Docker is an open platform for developing, shipping, and running applications. Docker enables developers to package applications into containers—standardized executable components combining application source code with the operating system (OS) libraries and dependencies required to run that code in any environment.

What is called Docker?

Containers, Images and Registries

  • A container is a standardized, isolated environment for running applications. Containers allow developers to package up an application with all of the parts it needs, such as libraries and dependencies, and ship it as one package.
  • An image is an inert, immutable, file that’s essentially a snapshot of a container. Images are created with the docker build command, and they’ll produce a container when started with docker run.
  • A registry is a library of images. Docker Hub is the default registry where you can find official images from vendors like Ubuntu, Redis, and MySQL. You can also host your own private registry.

Why Use Docker?

There are many advantages to using Docker:

  • Portability – Containers can run on any OS. This makes it easy to develop on one machine and deploy to another without compatibility issues.
  • Speed – Containers share the host OS kernel and start almost instantly. This allows for faster startup times compared to virtual machines.
  • Efficiency – Containers take up less space than VMs and consume fewer resources. You can easily run many containers on a single host.
  • Agility – Making changes and deploying new versions is fast and simple with containers. This facilitates continuous development and deployment.
  • Isolation – Each container runs in isolation from others for better security by default. Applications are also isolated from the underlying infrastructure.
  • Consistency – Docker assures that a container will always run the same, regardless of where you deploy it. This simplifies application management.

Docker Architecture

Docker utilizes a client-server architecture:

  • The Docker daemon runs on the host machine. It builds, runs, and distributes Docker containers.
  • The Docker client talks to the Docker daemon. It allows users to interact with Docker through a CLI or REST API.
  • A Docker registry stores Docker images. These registries can be public like Docker Hub or private within an organization.
  • Docker containers encapsulate a piece of software in a complete filesystem that contains everything it needs to run. This includes the application, runtime, dependencies, and libraries.

Basic Docker Concepts

Here are some key concepts and Docker-specific terminology:

  • Container – An isolated environment to run an application and its dependencies. Containers are created from Docker images.
  • Image – A read-only template that contains a container environment and metadata about how to run it. Images are used to create containers.
  • Docker file – A file with instructions Docker can use to build a Docker image automatically.
  • Docker Daemon – The backend service running on the host that manages building and running Docker containers.
  • Docker Client – The command line tool used to communicate with the Docker daemon to instruct it what to do.
  • Docker Hub – Docker’s public registry that hosts official images and enables users to host their own repositories.
  • Docker Compose – A tool that defines, runs, and manages multi-container Docker applications with YAML files.

Working With Docker Containers

Here is a quick overview of some basic commands for working with Docker:

  • docker build – Build an image from a Docker file
  • docker run – Run a container from an image
  • docker ps – List running containers
  • docker images – List images
  • docker pull – Pull an image from a registry
  • docker push – Push an image to a registry
  • docker stop – Gracefully stop a running container
  • docker rm – Remove one or more containers

Docker Benefits for Developers

Docker offers many advantages for developers:

Consistent Development Environments

Containers ensure all team members use the same tools, dependencies, and configs without manual setup. This leads to fewer bugs caused by environment differences.

Accelerated Onboarding

New developers can quickly spin up the necessary containers to start coding within minutes instead of spending days setting up their environment.

Simplified Dependency Management

Dependencies are packaged inside containers, avoiding version conflicts. Updating dependencies means rebuilding containers rather than modifying the development environment.

Streamlined CICD Pipelines

Docker enables standardized artifacts to move smoothly through the development delivery lifecycle. Images become the build artifacts handed off between teams.

Overall, Docker prevents environment inconsistencies and repetitive setup tasks so developers can focus on writing code. Teams can ship updates faster and more reliably using containers.

Docker Benefits for Operations Teams

In addition to aiding developers, Docker also assists IT operations teams with:

Increased Infrastructure Efficiency

More containers can run on a single OS than VMs, which maximizes resource utilization and cuts infrastructure costs.

Accelerated Deployments

Containers start almost instantly and have lower overhead than VMs. Operations teams can deploy updates faster with less downtime.

Environment Consistency Across Environments

An image containing an application will run the same way regardless of whether it’s on a developer laptop or a production server.

Infrastructure Abstraction

Containerized applications abstract infrastructure complexities. The operational environment is portable and can easily move between on-prem data centers and the cloud.

By leveraging containers, ops teams gain velocity and reliability while optimizing resource usage. Docker empowers continuous delivery best practices.

When Should You Use Docker?

Here are a few examples of good use cases for Docker:

  • Creating isolated development environments for your applications
  • Speeding up onboarding for new team members
  • Simplifying deployment of development code to test environments
  • Supporting continuous integration and delivery (CI/CD) workflows
  • Deploying microservices applications
  • Moving applications between different infrastructures or cloud providers
  • Creating standardized environments across staging, QA, and production

In general, if you have issues with environment consistency, slow setup times, unreliable deployments, or technology lock-in – Docker can probably help.

Limitations of Docker

While very useful, Docker does have some limitations:

  • Learning curve – Docker utilizes its own terminology and CLI commands which takes time to learn.
  • Security vulnerabilities – Images may contain vulnerabilities unless careful checks are in place. Keeping images patched is critical.
  • Legacy app support – Some legacy or specialized apps may be challenging to containerize properly.
  • State management – Containers themselves are stateless and do not preserve data after shutdown. This requires planning for lifecycle management using volumes or orchestration.
  • OS dependencies – Docker still relies on host OS kernels, limiting some features to Linux-based environments. Support for Windows and macOS is improving.

Overall, Docker revolutionizes application development and deployment in many scenarios. But teams should carefully evaluate if it fits their systems and is worth the operational investment to implement properly.

Key Takeaways

  • Docker utilizes containers to allow developers to package applications into standardized units along with their operating system dependencies.
  • Containers provide consistent environments, simplified dependency management, accelerated deployments, and infrastructure abstraction benefits.
  • With its client-server architecture and public registries, Docker enables agile application lifecycle management.
  • Docker is well-suited for isolating environments, moving applications between infrastructures, and supporting CI/CD pipelines.
  • Teams should consider Docker’s learning curve and plan for lifecycle management when evaluating it.


Docker has quickly become an incredibly useful platform for development teams over the past decade. Leveraging containers and images provides major improvements in portability, efficiency, and agility.

By encapsulating infrastructure dependencies into immutable containers, Docker allows code to run reliably when moved between different environments. This facilitates continuous delivery pipelines and microservices architectures.

While containers do have some limitations and operational considerations, they offer immense value. For most modern application scenarios, Docker enables cleaner local setups, standardized deployments, and simplified maintenance.

Evaluating if and how to effectively utilize Docker is highly worth any development or operations team’s time and effort today. Overall, Docker aims to empower innovation by simplifying IT complexity – allowing technology professionals to focus on solving business problems rather than infrastructure blockers.

Frequently Asked Questions

  1. What are the key benefits of using Docker?
    The main benefits of Docker are portability, speed and efficiency. Containers standardize environments across machines so you can build once and run applications anywhere. Containers also start instantly to deploy faster. Plus Docker optimizes infrastructure resource usage.

  2. What does a Docker file do?
    A Docker file contains instructions to automate building a Docker image. This allows you to repeatedly build custom images with your applications and dependencies packaged inside ready to run as containers.

  3. Do I need Docker installed locally to develop applications?
    Yes, having Docker locally makes developing containerized applications simpler by providing quick iterative testing. You can utilize a small footprint Docker installation like Docker Desktop.

  4. Can Docker only run Linux containers?
    No, Docker also supports Windows containers allowing you to choose which works best per application. Docker utilizes the host operating system’s kernel but abstracts the hardware differences.

  5. How is Docker different than a virtual machine?
    Docker containers share the host operating system kernel and startup is near instant since a full guest operating system boot is avoided. This makes containers extremely fast and lightweight compared to traditional virtual machines.

  6. Is Docker secure?
    Docker has many built-in security features including process, network, storage and credential isolation between containers and hosts. Images should be scanned and kept patched. Proper access controls and infrastructure hardening is still critical for production use.

  7. Can Docker scale horizontally?
    Yes, Docker ships with tooling like Swarm and Kubernetes built-in that support scaling out containers across multiple host machines. You can add hosts as needed to scale capacity.

  8. How do I make Docker data persistent?
    Docker provides volumes which are file systems mounted into containers to persist data beyond the container’s lifecycle. There are also volume plugins and storage drivers to integrate external and network storage systems.

  9. Does Docker work with continuous integration / continuous delivery (CI/CD)?
    Yes, Docker naturally fits into CI/CD pipelines. Container images become the build artifacts transferred between environments. Infrastructure disparities are abstracted away so code flows smoothly through the pipeline.

  10. Can I run Docker on the cloud?
    Yes, all major cloud providers support running Docker containers natively including AWS, Google Cloud, Azure and more. The containers remain portable to run on-prem or move between cloud vendors.

  11. Is there significant overhead running Docker containers?
    Containers have extremely minimal size and startup overhead which maximizes performance. The only requirement is having a Docker Engine installed on the host operating system. The rest is taken care of automatically.

  12. How do I control Docker containers?
    The Docker client CLI allows control to start, stop and manage containers. For production use, container orchestration platforms like Kubernetes facilitate running containers at scale while handling health monitoring and failover.

  13. Can multiple applications run on one Docker host?
    Yes, you can deploy any number of applications using varying containers on a single Docker host. Adding more disk, CPU, and memory allows expanding capacity for more workloads. Network communication between containers is simple.

  14. Is Docker compatible with continuous deployment?
    Yes, Docker enables continuous deployment strategies since images can rapidly launch containers in standardized environments consistently everywhere. This facilitates frequent production updates with minimal overhead.

  15. Can containers connect to external databases or services?
    Yes, containers can integrate external resources using service discovery or direct network connections. Containers appear on virtual networks alongside physical hosts allowing connectivity.

  16. How do I configure Docker containers?
    Containers behavior is configured through arguments passed to docker run, environment variables, networking ports exposed, or volumes mounted inside. Many images accept additional parameters to customize settings per deployment.

  17. What language is Docker written in?
    The Docker project utilizes Google’s Go programming language (golang) due to its portability across operating systems. This allows the Docker client and daemon to run on many platforms.

  18. Who maintains and supports Docker?
    Docker was created by dot Cloud which was renamed to Docker, Inc – the core company that maintains the open source Docker project across over 18,000 community contributors comprising vendors, partners and end-users.

  19. Where can I learn more about Docker online?
    Docker provides extensive official documentation and training material at https://docs.docker.com/. There are also many Docker books, video courses, tutorials, blogs and community forums available to continue learning.

  20. How do I monitor Docker container performance?
    There are several useful Docker tools for monitoring including native options like docker stats or accessing container logs. Many monitoring systems like Prometheus, Datadog, and Grafana have Docker monitoring capabilities. Resource usage can be tracked at either the container or host level over time.

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