What is Docker: A Comprehensive Guide

It is an open-source project that helps you to automate the deployment of software applications using packaged applications known as containers on top of an Operating System (OS). So, you can also term it “OS-level virtualization.” Each container provides an isolated environment like a Virtual Machine (VM). Unlike VMs, Docker containers do not need a full range of OS capabilities. The host’s kernel is shared and virtualized at the software level.

To sum up, Docker is a tool that allows developers, system administrators, etc., to easily deploy their applications in a sandbox (containers) to run on the host OS, which is Linux. Containers encapsulate everything needed to run an application, from packaging the OS dependencies to your source code. You can easily define a container’s creation steps as instructions in a Dockerfile. Docker uses Dockerfile to define an image.

The following are some of the key differences between Docker and VMs that allow you to make more informed decisions in the long run:

• Docker contains a Docker engine layer, whereas the virtual environment has a hypervisor layer.
• Memory usage is quite low when it comes to the Docker environment. With a VM, memory usage is very high, and you can easily run into memory issues.
• With Docker, the performance is always high and top-notch because you are working with a single Docker engine. The performance tends to be poor when you have more than one VM on a server.
• In terms of portability, VMs are not ideal. They have a huge dependency on the host OS, and you can encounter a lot of problems, especially when you are working with VMs. Docker is designed from a portability perspective. You can manage your solutions easily with Docker containers, ensuring the solution can function irrespective of where it is deployed.
• The time for a VM to get started is slow compared to the boot-up time for a Docker environment, as it is almost instantaneous.

You can install Docker on your desktop machine and start right away in a few minutes.

• You must select the correct OS to download Docker. Docker comes with comprehensive documentation that helps you to get started using Docker.
• Once you have downloaded Docker, you can refer to the Getting Started guide to create a new web server with Docker.
• You can use the following command for downloading the docker/getting started image from the Docker hub and start it in a container: $ docker run -d -p 80:80 docker/getting-started

Fast and Consistent Delivery of Your Applications

Docker plays an important role to streamline the development lifecycle by allowing the development teams to work in a structured environment using local containers. Containers help you to achieve seamless Continuous Integration/Continuous Deployment (CI/CD) workflows.

Quicker Deployment Capabilities

Docker’s container-based platform allows you to manage complex workloads easily. Docker containers can run on a developer’s local laptop, physical machines or VMs in a data center or a mixture of environments. Docker’s portability and lightweight nature enable it to scale up or tear down applications and services in real-time.

Handling More Workloads on the Same Hardware

Docker is lightweight and fast in overall execution. It allows you to provide a cost-effective alternative to hypervisor-based VMs, so you can handle more server capabilities to achieve desired business objectives. Docker is useful for small and medium deployments where you can achieve more with fewer resources.

Docker works on a client-server architecture. The Docker client interacts with the Docker daemon, the chief component in the Docker architecture. It helps to build, run, and distribute Docker containers. The client and Daemon can be executed on the same machine, or you can also connect a Docker client remotely to a Docker daemon. The Docker client and daemon communicate using REST API, UNIX sockets, or network interface. There is another Docker client known as Docker compose that allows you to work with applications that consist of a set of containers. The image below displays Docker’s client-server architecture.

The following are some of the key components that are part of Docker architecture:

• Docker daemon can interact with Docker API requests and handle different objects as part of Docker Architecture. Docker daemon can be associated with other daemons to manage Docker-related services.
• The Docker client is an integral component that allows different users to interact with Docker. The Docker client can also communicate with more than one daemon.
• Docker desktop applications can be easily installed on your Mac, Windows, or Linux environment, which allows you to manage containerized applications and microservices.
• The Docker registry allows you to manage Docker images easily. Docker Hub is accessible to everyone, and it follows a standard configuration to search for images on Docker Hub by default. When you are executing pull or run commands, the images can be fetched from the registry that is configured.
• Images are read-only templates with predefined instructions used to create a Docker container. You can create your images, or you might only use the ones created by others and published in a registry.
• The Container allows you to manage different container operations right from creation, start, move, to delete using either the API or CLI capabilities.

Many industries and leading companies have shifted their infrastructure to containers or rely on containers in some other way. The following are the leading industries that use Docker:

• Energy
• Entertainment
• Financial
• Food Services
• Retail
• Social Networking
• Telecommunications
• Travel
• Healthcare

The following are the top 5 advantages of using Docker:

Consistent Environment

Consistency is one major benefit of Docker that makes it a unique choice from the other options. Developers can easily run an application in a consistent environment from design to development to production to maintenance. The application shows the same behavior in different environments, denoting that you can easily eliminate production-related issues. With a more predictable environment, developers can easily introduce more quality features rather than debugging errors and resolving compatibility issues.

Speed and Agility

Speed and agility are other key advantages of Docker. You can instantly create containers of every process and deploy them within a fraction of a second. The process is highly lightweight as you are not involved in configuring the OS. You can easily create, destroy, start, or stop a container. Docker helps to improve the speed and efficiency of the CI/CD pipeline as you can create a container image and use it across the pipeline while executing non-dependent tasks in parallel. You can improve overall productivity with support for version control that allows you to roll back to the previous version instantly.

Highly Secure

Docker environments are highly safe. The applications executed using Docker do not interact with each other. The containers cannot check the processes that are executed in another container. Each container contains its own set of resources and has no interaction with the resources available in other containers. The resources used are only allocated to them. You can easily manage the traffic flow. The container can also be easily deleted once the application reaches its end of life.

Efficient in Managing Multi-Cloud Environments

Multi-cloud environments have become quite popular recently. The multi-cloud environment is all about handling unique cloud requirements, which are managed using a different infrastructure altogether. This is where you can rely on Docker containers for movement across any environment. For example, you can run a container in an AWS EC2 instance and then easily migrate to the Google Cloud platform with utmost ease.

Affordable Pricing

It is all about delivering high-value features with top-notch performance and optimized pricing. It is all about getting the required Return on Investment (ROI). The positive aspect of Docker is that it allows you to reduce infrastructure costs considerably. You can run applications at minimal costs compared to VMs and other technologies.

Continuous Integration

Regarding continuous integration, Docker can work well as part of its pipelines along with tools such as Jenkins, Travis, etc. These Docker tools can save the new version as a Docker Image whenever updates are done in the source code. A unique version number is assigned, and changes are pushed to Docker Hub, which is deployed to the production environment.

Some of the disadvantages of Docker are listed below:

Not Suitable for Applications with Graphical Interfaces

Docker allows you to manage applications that are executed using the command line. You can execute a graphical interface inside a Docker container, but it is not a great solution in the long run. Docker is not well suited for applications that require rich graphical interfaces. This is where Docker needs a big improvement.

Dependencies on the Data Available in the Container

There are too many dependencies on the container that contain the data requirements. There are instances when a container is unavailable, which means that you need to have a strategy in place to counter such a scenario.

Cross-Platform Compatibility Issues

This is a common limitation faced by Docker when compared to VMs. When you are running an application in a Docker container on Windows, it would not be possible to run it on Linux and vice versa. This limitation makes Docker a less favorable choice in some highly heterogeneous environments composed of Windows and Linux servers.

Not All Applications Get True Benefits from Containers

In general, only a set of applications can benefit from containers in the long run. Applications that are executed using microservices can gain the most from containers. The real benefit of Docker lies in simplifying the application delivery by providing an easy packaging mechanism.

Docker is a powerful tool full of extraordinary system capabilities. The following are some of the top reasons why you should learn Docker when you are just getting started:

• Docker applications are independent of the OS requirements. You only need to update and secure the OS of your host system, allowing you a lot of flexibility to do other things with utmost ease.
• Each of the Docker apps has its unique set of dependencies. You do not have to worry about library versions being clashed.
• The images are maintained on the Docker hub, which makes it possible to set up the entire application environment using a single command.
• The single-line command used to set up the environment can be easily automated like any other command-line tool.
• You can easily learn Docker as an absolute beginner because there are not many complexities involved in implementation and execution.
• Docker is used in the production system, but it is a tool that can be used for running the same application on a developer’s laptop or server. Docker can be easily moved from development to testing to production without making any alterations. You can build a CI/CD pipeline if you are just starting your Docker journey.

The future of Docker jobs looks promising, with more and more companies looking to adopt Docker in their current scheme of things. It is a huge and fast-growing field. Technology is evolving, and there are no surprises that the demand for Docker Software developers and programmers will remain high in the market.

According to the SD Times report, the role of Docker engineer has seen a 225% jump in postings on Indeed. According to Indeed and Angels, 80% of the companies pay more than $90,000 starting salaries to a Docker DevOps engineer, which is huge. An entry-level Docker engineer with less industry experience and expertise(<1 year) can earn a handsome salary package of ₹ 364,926. With a huge demand for exceptional talent, you will see more and more companies hiring a lot of Docker engineers soon.

Containers offer more benefits for distributed applications, particularly microservices, than standalone ones.  Each service follows the containerized approach and can be executed using an orchestration tool such as Kubernetes, which allows you to reduce resource overhead on applications that are loaded with many features. 

Cloud providers with public and private service offerings can use Kubernetes for their container services. This helps to make container deployment in the cloud environment a lot more seamless. Kubernetes has come a long way in cementing its popularity as the leading container orchestration provider.

According to the Diamanti Survey in 2019, more than 500 IT organizations revealed that security was one of the top challenges along with technology, followed by infrastructure integration. Since 2020, there have been a lot of developments to improve the container and security experience.

The focus on security is also highlighted in the recent containerization usage reports in 2022:

• Sysdig’s 2022 Cloud-Native Security and Usage Report found that 75% of the respondents were running containers with high or critical vulnerabilities, and 76% had containers running as root, which is dangerous from an IT ecosystem safety perspective.
• In the Red Hat 2022 State of Kubernetes Security Report, 93% of the respondents reported that there was at least one Kubernetes-related security incident within the prior 12 months, with 31% experiencing revenue or customer losses.

With the wide adoption of containers soon, it becomes important to address these concerns sooner rather than later.

There are a lot of online courses available on leading e-learning platforms such as Udacity, Coursera, and others that can help you to learn Docker basics if you are an absolute beginner. Another online learning platform Careervira provides highly affordable and customized courses based on your learning requirements.

Introduction to Docker by O'reilly

Careervira provides a list of trending courses so that professionals can opt for such courses without having to think twice. This course has gained a lot of popularity in the past few months as it comes with hands-on training, allowing you to understand the Docker fundamentals in a much better way. If you are a beginner looking to gain skills related to Kubernetes, Docker Networking, Puppet, Ansible, and Docker, this course will provide the best technical value from a learning perspective.

Docker for Absolute Beginners by Coursera 

This is another trending course for absolute beginners, which is short and crisp (only 2 hours). It helps you to understand Docker architecture, different Docker commands, and complex deployments using Docker containers. The self-paced course is easily accessible from either a Desktop or Laptop, based on your requirements. The case studies and capstone projects allow you to understand project-related challenges in real-time.

Docker Fundamentals by O’reilly

This is the third most preferred course for learning the fundamentals of Docker. This course works best for beginners and Docker enthusiasts who wish to use Docker images and containers. If you are a system administrator or system architect, this course will surely add more value to your existing skill set. You can learn about building your first Docker container and deploying applications within a container. The 4.5 of 5 rating indicates the true value offered by this course.

Docker Certification Training Course by Edureka

Careervira also provides access to various certification training courses related to different cutting-edge technologies, such as Docker. The duration of this course is 4 weeks, which is well suited to meet beginner learning requirements. The instructor-led certification course gives you hands-on experience with various storage strategies, which includes deploying multi-container applications. The real-world industry use cases allow you to handle complex challenges, which are great from a learning perspective. Professionals can also get required job assistance if they are looking to make a transition or career move as a Docker engineer.

Docker for Web Developers by Pluralsight

This course is useful as it helps you to use Docker open platform to create applications that can work seamlessly on any machine. The course is designed especially for web developers who want to learn Docker tools and associated commands. If you are a beginner and are looking for a self-paced teaching course, then help you to learn Docker Swarm, Docker Container, Docker Networking, and Security, as well as Docker Compose.

Note: The courses are designed keeping in mind the learning needs and current market trends; hence, the courses provide true value to professionals looking to upskill and upgrade their existing skill sets.

We have discussed what Docker is, its core features and its capabilities at length. Docker will surely become the future of virtualization as well. Its popularity is growing with leading companies like Netflix, Spotify, etc., using the containerized approach. If you are an organization looking to leverage Docker capabilities, the right time is now as the market trends change drastically.