Docker is an essential tool that is used in a lot of projects. In this article, we will be discussing the most important elements and tools around the Docker ecosystem when getting started as a beginner. Let’s get started by exploring more about Docker. What is Docker? When attempting to run code on other machines, we must provide our source code as well as dependencies such as libraries, databases, web servers, and so on. Docker is an open-source tool that automates the deployment of an application within a virtual container (similar to normal shipping containers), allowing separated applications to be shipped or deployed as an independent system, hence eliminating the problem of environment inconsistency. Docker started out as a project to construct single-application LXC (Linux Containers), offering a number of changes to LXC that made containers more portable and flexible to use. It grew into its own container runtime environment over time. Docker is a Linux application that allows you to easily create, deploy, and operate containers. With the emergence of containers, microservices architecture emerged. Containers enabled applications to be broken down into the smallest components or "services" that serve a specific purpose, and those services to be created and deployed independently of one another rather than as part of a single monolithic entity. Why do we need Docker? The main benefits of Docker are as follows: Faster Development Process Third-party apps or libraries such as PostgreSQL, Redis, Elasticsearch, and others do not need to be installed on the system when using Docker; instead, they may be executed within the container. It also allows you to run multiple versions of the same application on the same machine at the same time. In addition, depending on the technology stack, you may handle many programming language versions in Docker containers, such as Python 3.7 or Python 3.9, and so on. Handly Application Encapsulation Docker containers offer a simple and convenient encapsulation solution for delivering or distributing your application in one piece, complete with all essential dependencies. Furthermore, because Docker supports several programming languages, it provides a consistent image format for distributing your application across multiple host systems and cloud services. Containers can therefore help development teams in improving the convenience and speed of the development process. Consistent Code Behavior in different environments Docker containers lower the probability of error caused by multiple operating system versions, system dependencies, and so on, assuring consistent behavior on a local machine, development, staging, and production servers. Easy and Clear Monitoring Docker containers allow you to incorporate an external logging driver for a single view of logs from all operating containers, facilitating quick and straightforward application monitoring. It also implies fewer and easier security upgrades. Easy to Scale Because Docker containers are smaller in size, a single physical system may host several containers. Furthermore, less code is required to move, migrate, and upload workloads. How is it different from Virtual Machines? Virtualization is used by both Docker and Virtual Machines to help you optimize the available computer resources. However, unlike a VM, containers only virtualize the operating system rather than the entire machine. Containers run on top of a physical server and its host operating system, which is commonly Linux or Windows, and share the host OS kernel, binaries, and libraries. The shared components in this case are read-only. Sharing OS resources such as libraries reduces the need to repeatedly recreate OS code, and a server may execute different workloads with a single OS installation, making containers incredibly lightweight. They are generally only a few megabytes in size and require only a few seconds to start, whereas VMs take minutes to function and are frequently measured in terabytes. To sum it up: VMS CONTAINERS Heavy in weight Lightweight Limited performance Native performance Each VM runs in its own OS All containers share the same host OS Hardware-level Virtualization OS Virtualization Startup time in minutes Startup time in milliseconds Allocates required memory Requires less memory space Fully isolated and hence more secure Process-level isolation, possibly less secure To summarise: Virtual machines (VMs) help organizations make the most of their infrastructure resources by increasing the number of computers that can be squeezed out of a limited amount of hardware and software. Containers make microservices and DevOps processes possible, allowing organizations to maximize their development resources. Docker Basics and Terminology Here are some of the basic Docker concepts explained in a brief and practical manner: Containers Containers are application instances that run and encapsulate required software. Images are always used to create containers. To connect with other containers or the outside world, a container might expose ports and volumes. Containers can be instantly destroyed/deleted and recreated in seconds. Containers do not preserve their original state. Images An image is a blueprint that may be used to build any number of containers. It includes all of the necessary components for each container. Every stage of the image creation process is saved and reusable (Copy On Write model). Consider it a highly specific step-by-step instruction, such as what operating system to install, what files to place where, what packages to install, and what the finished machine is expected to do. Images cannot be changed, however, you may create a container from an image, execute operations on it, then save another image based on the container's current state. An image contains no commands that are presently executing. Thus, starting a container is similar to restarting a system after it has been powered off. When launching a container from an image, you often do not rely on the defaults to be right; instead, you add arguments to the command being run, mount volumes (data directories) with your own data and configurations, and wire up the container to the host's network in a way that works for you. Port In its original sense, a port is a TCP/UDP port. To simplify matters, consider that ports can be exposed to the outside world (available from the host OS) or linked to other containers (accessible exclusively from those containers and invisible to the outside world). Volume Volume is analogous to a shared folder. Volumes are initialized when a container is created. Volumes are designed to hold data independent of the lifespan of the container. Registry The Registry is the server that stores Docker images. Similar to GitHub, you may download an image from the registry and deploy it locally, as well as push locally developed images to the registry. Dockerfiles A Dockerfile is a set of exact instructions that describe how to construct a new Docker image, as well as how to configure defaults for containers that run on it. In the best-case scenario, it will generate an identical picture for everybody executing it at any moment. Dockerfiles are similar to project setup instructions but in executable code. A script that installs the operating system, and all required components, and ensures that everything else is in place. In a Dockerfile, you usually specify which image to use as the "starting point" for subsequent operations (FROM), after which you can run commands (starting containers from the previous step's image, executing it, and saving the result as the most-recent image) (RUN), and copy local files into the new image (COPY). When launching a container from this image, you usually additionally supply a default command to run (ENTRYPOINT) and the default parameters (CMD). DockerHub Docker Hub is a web-based registry maintained by Docker Inc. It contains a big number of Docker images with varied software. Docker Hub is a repository for "official" Docker images generated by the Docker team or in partnership with the creator of the original software (this does not always imply that these "original" images are from official software manufacturers). Their shortcomings are listed in official images. This information is accessible to any logged-in user. Accounts may be accessed in both free and paid versions. You can have one private image and an infinite number of public images per account. Docker Store Docker Store is a comparable offering to Docker Hub. It's a marketplace featuring ratings, reviews, and other features. Conclusion Docker might be frightening at first, especially with so much hype around it. With the information presented here, you should have a clear knowledge of what Docker is about at its core, as well as the ability to ask the relevant questions in order to be assured about what single concepts are about and why they are useful. If you want to pursue practical courses or go further into more challenging topics, this is a fantastic place to start. With these ideas, you'll be able to comprehend all of the new tools that surround it and decide whether they'll improve your coding life or not.

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