What is Docker? A comprehensive overview

Docker is an open-source software platform used to develop, deploy, and manage applications. It enables you to separate your application from your infrastructure by providing the ability to package and run the application in a loosely isolated environment called a container. The platform eliminates the need for mundane and recurring configuration tasks across the development lifecycle for rapid, convenient, and highly portable cloud and desktop application development.

The extensive end-to-end platform provided by Docker consists of different modules like user interfaces, application programming interfaces, command-line interface, and security mechanisms. These modules work in collaboration with each other throughout the delivery lifecycle of an application to provide a consistent development platform for the developers.

What are Docker containers?

The Docker containers serve as standard executable components that combine the operating system libraries, application source code, and their dependencies for a consistent and smooth deployment in any infrastructure. The Docker containers provide virtualization and process isolation capabilities separating the application from the operating system kernel. Some of these capabilities include control groups which are used for the allocation of resources; and namespaces which are used for restricting process visibility or access to system resources.

These containers also enable the sharing of single instance resources of the host OS similar to hypervisors in virtual machines - which share memory, resources, and CPU of the hardware server. Thus the container framework is able to provide all the features as well as benefits of virtual machines: cost-efficiency, scalability, disposability, and process isolation in application development. Let's have a look at some of the prominent container features.

Docker Container features

Here are some of the core features and benefits of containers that make it one of the preferred development tools for applications in the software industry.

• Lightweight functionality: The containers are incredibly light, unlike virtual machines that carry the load of a hypervisor and the entire OS instance. The containers only include operating system dependencies and processes essential for executing the code. The container sizes are generally limited to megabytes, unlike virtual machines taking up gigabytes. This provides better utilization of hardware capability resulting in quicker startup times.
• Better development productivity: In contrast to virtual machines, the containers provide easier and faster deployment, restart, and provisioning of applications. This is why containers are ideal for use in CI/CD pipelines, and they serve as a better option for the developers that adopt DevOps or Agile practices.
• Increased resource efficiency: The containers provide faster turnaround times, and enable concurrent execution of multiple application instances on the same hardware architecture as you do with virtual machines. This also helps increase resource efficiency, thereby reducing the expenditure on cloud infrastructure.

The different Docker tools and components

Docker technology has become incredibly popular with software developers since it provides a unique way of packaging the tools to create and launch the container in a structured manner. There are various Docker tools and components that are commonly used during application development. We will have a brief look at these tools and components.

1. DockerFile: Every Docker container begins with a text file containing instructions on building a Docker container image. The Dockerfile is responsible for automating the Docker image creation process. It contains a list of CLI instructions, detailing the environment variables, network ports, file locations, and other essential components, to be run by the Docker engine for assembling the image.
2. Docker image: The Docker image provides all the information including the source code, libraries, dependencies, and tools that the application needs for running as a container. It is an executable, read-only, and portable file with instructions for creating a container and the different software components that will be run by the container. While it is possible to build Docker image right from scratch, most developers use it from common repositories.

The Docker image consists of various layers and these layers correspond to the image version. When changes are made to the image, a new layer is added at the top and it replaces the previous layer thus assuming the current image version. The previous layers are stored for reuse in different projects or rollbacks.

1. Docker hub: The Docker hub is the public repository consisting of container images that can be shared, stored, and managed efficiently. It is an extensive repository with over 100k images sourced from individual developers, software vendors, and open-source projects. The Docker hub can be considered as Docker’s version of GitHub, specially made for the containers. It has certified images from Docker’s trusted registry, images made by Docker Inc., and a host of other images.
2. Docker engine: The Docker engine can be considered the core component of Docker. The client-server technology that powers the Docker engine is used to create and run containers. The Docker engine consists of a daemon process known as Dockerd and it is responsible for managing containers, command-line interface, and the application programming interfaces that enable programs to interact with the daemon.
3. Docker registry: The Docker registry is an open-source, scalable system for storing and distributing Docker images. This registry enables the developers to keep track of image versions located in the repositories through identification tagging. This is usually done with the help of git - a tool for version control.
4. Docker daemon: The Docker daemon is the background service that runs on different operating systems including Windows, iOS, and macOS. This service is responsible for the creation and management of Docker images. The daemon implements the commands from the clients, serving as the control center for the deployment of Docker.
5. Docker desktop: All the components are packaged within the Docker desktop application, thus providing a convenient way of building and sharing microservices and container applications. It provides a user-friendly interface for executing and managing the different modules of Docker.

Deployment and management of Docker

If you have a limited number of containers then it is fairly easy to manage the entire application within the Docker engine. However, if the Docker deployment consists of a large number of services and containers then it becomes unrealistic to manage the workflow. There are custom tools built for managing the higher volume of containers in an application.

Docker Compose: If you have a multi-container application with numerous processes, then the Docker compose can be used for managing the application architecture. Docker compose is a command line for creating YAML files that provide the specifications for the different services.

Docker compose also provides the capability of creating and managing services from the configuration and tracking the status and log output of all the benefits that run in the containers. It also provides additional capabilities of documenting and configuring service dependencies, specifying base nodes, and defining persistent storage volumes.

Managing Docker: Docker has its own orchestration tool known as Docker Swarm for monitoring and managing container lifecycles in complex environments. However, there is an efficient alternative to Docker Swarm in the form of Kubernetes, which is preferred by a lot of developers.

Kubernetes is the open-source platform used to schedule and automate tasks in container-based architecture. Kubernetes provides various services that include deployment of containers, service discovery, updates, health monitoring, load balancing, and storage provisioning among others.

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Docker benefits and drawbacks

While Docker provides a host of advantages to the application developers. However, it also comes with a few drawbacks. Here we will outline the major benefits and drawbacks associated with Docker.

Benefits:

Convenient portability: Docker enables the creation of a clean and minimal environment through isolation. This aids in highly granular control and provides seamless as well as convenient portability.

• Excellent orchestration and scaling: Since the Docker containers are incredibly lightweight, it allows developers to create multiple containers for high scaling objectives and services. The container cluster then requires orchestration which can be effectively achieved through Kubernetes.
• Container versions: Docker allows tracking of container image versions thereby paving the way for roll-back functionality and increased transparency on information about different versions. It also allows uploading only the deltas between the new and existing versions.
• Easy composability: The Docker containers facilitate the creation of application building blocks in a modular format having simple interchangeable components. This helps in speeding up the development life cycle including bug fixes and feature releases.

Drawbacks:

• Isolation: While the Docker containers provide numerous advantages over virtual machines, one aspect where VMs are slightly better is the isolation. The virtual machines implement stricter isolation in comparison to the containers.
• Short of bare metal speed: The Docker containers are incredibly lightweight and thus provide better speeds than virtual machines. However, they do have some degree of performance overloads which means that their execution falls just short of the bare metal speed, which might be needed in some rare application requirements.
• Lack of inherent persistence: The containers can boot and run from the images that specify their details. However, once the image has been created, it doesn’t change. On the other hand, the container instances are transitory, and once removed from the memory; they are gone without persistence. If you want persistence for your container instances across sessions, the developers specifically need to design for the persistence parameters, unlike virtual machines with inherent persistence.

The current status of Docker in the industry

The use of Docker containers has continued its upward trend as an increasing number of enterprises are now moving to cloud-based architecture for their applications and software modules. The Docker containers are an important part of cloud-based modules as they prevent the developers from being restricted to any one vendor.

The Docker containers have opened the avenue for building and running workloads anywhere, including the cloud, and it is done through consistent implementations and optimization of IT infrastructure. If you are looking for experienced Docker developers to lead your software projects then you can hire the best Docker developers in 2023 at Turing

Wrapping up

The Docker containers continue to provide value to software developers by optimizing the development and deployment of applications using lightweight modules. With the constant evolution in the technology and introduction of new frameworks, the Docker containers also need to expand for future scaling and collaboration with the evolving tech stack.