All about Docker for beginners

Introduction

Docker is an open source platform that enables developers to build, deploy, run, update and manage containers — standardized, executable components that combine application source code with the operating system (OS) libraries and dependencies required to run that code in any environment

containers

Containers are instances of Docker images that can be run using the Docker run command. The basic purpose of Docker is to run containers. Let’s discuss how to work with containers.

How Docker works

Docker works by providing a standard way to run your code. Docker is an operating system for containers. Similar to how a virtual machine virtualizes (removes the need to directly manage) server hardware, containers virtualize the operating system of a server. Docker is installed on each server and provides simple commands you can use to build, start, or stop containers.

Docker tools and terms

Docker File

Every Docker container starts with a simple text file containing instructions for how to build the Docker container image. Docker File automates the process of Docker image creation. It’s essentially a list of command-line interface (CLI) instructions that Docker Engine will run in order to assemble the image. The list of Docker commands is huge, but standardized: Docker operations work the same regardless of contents, infrastructure, or other environment variables.

Docker images

docker images contain executable application source code as well as all the tools, libraries, and dependencies that the application code needs to run as a container. When you run the Docker image, it becomes one instance (or multiple instances) of the container.

It’s possible to build a Docker image from scratch, but most developers pull them down from common repositories. Multiple Docker images can be created from a single base image, and they’ll share the commonalities of their stack.

Docker containers

Docker containers are the live, running instances of Docker images. While Docker images are read-only files, containers are life, ephemeral, executable content. Users can interact with them, and administrators can adjust their settings and conditions using Docker commands.

Docker Hub

Docker hub is the public repository of Docker images that calls itself the “world’s largest library and community for container images.” It holds over 100,000 container images sourced form commercial software vendors, open-source projects, and individual developers. It includes images that have been produced by Docker, Inc., certified images belonging to the Docker Trusted Registry, and many thousands of other images.

All Docker Hub users can share their images

Docker Desktop

Docker Desktop (link resides outside ibm.com) is an application for Mac or Windows that includes Docker Engine, Docker CLI client, Docker Compose, Kubernetes, and others. It also includes access to Docker Hub.

Docker daemon

Docker daemon is a service that creates and manages Docker images, using the commands from the client. Essentially Docker daemon serves as the control center of your Docker implementation. The server on which Docker daemon runs is called the Docker host.

Docker registry

A Docker registry is a scalable open-source storage and distribution system for Docker images. The registry enables you to track image versions in repositories, using tagging for identification. This is accomplished using git, a version control tool.

Docker deployment tools

When running just a few containers, it’s fairly simple to manage an application within Docker Engine, the industry de facto runtime. But for deployments comprising thousands of containers and hundreds of services, it’s nearly impossible to manage the workflow without the help of some purpose-built tools.

Docker plugins

Plugin can be used to make Docker even more functional. A number of Docker plugins are included in the Docker Engine plugin system, and third-party plugins can be loaded as well.

Docker Compose

Docker Compose to manage multi-container applications, where all containers run on the same Docker host. Docker Compose creates a YAML (.YML) file that specifies which services are included in the application and can deploy and run containers with a single command. Because YAML syntax is language-agnostic, YAML files can be used in programs written in Java, Python, Ruby and many others languages.

Developers can also use Docker Compose to define persistent volumes for storage, specify base nodes, and document and configure service dependencies.

Kubernetes

Monitoring and managing container lifecycles in more complex environments requires a container orchestration tool. While Docker includes its own orchestration tool (called Docker Swarm), most developers choose Kubernetes instead.

Kubernetes is an open-source container orchestration platform descended from a project developed for internal use at Google. Kubernetes schedules and automates tasks integral to the management of container-based architectures, including container deployment, updates, service discovery, storage provisioning, load balancing ,health monitoring, and more.

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