THE BASICS: A Beginner’s Guide to Docker

Edward Kisller
2021-04-26 09:51

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Docker has rapidly emerged as the technology of choice for packaging and deploying modern distributed applications. Its name has become synonymous with containers. But what exactly is Docker, how does it work, and why should you use it? Read on and we'll explain the key concepts and features of Docker, as well as the benefits it brings to enterprise IT. We'll also show how you can get the most out of your Docker container environments.

Before we do any of that, let’s first tackle the fundamentals of containers.

Containers 101

If this is totally new territory to you, you'll likely be asking: What are containers, anyway? Briefly stated, containers are an alternative to the traditional virtualization method, which uses virtual machines (VMs) to partition infrastructure resources. But where VMs are fully fledged guest operating systems, containers are significantly more streamlined operating environments, which provide only the resources an application actually needs to function. This is made possible due to the way containers are abstracted from the host infrastructure. Instead of using a hypervisor to distribute hardware resources, containers share the kernel of the host OS with other containers.

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This can significantly lower the infrastructure footprint of your applications, as containers can package up all the system components you need to run your code without the bloat of a full-blown OS. The reduced size and simplicity of containers also means they can stop and start more quickly than VMs thus making them more responsive to fluctuating scaling requirements. And unlike a hypervisor, a container engine doesn’t need to emulate an entire OS. Taken as a whole, containers generally offer better performance when you compare them to more traditional VM deployments.

Containers and the Cloud

Containers are ideally suited to today's cloud approach to application architecture where, instead of relying on one, large monolithic program, you can break things up into a suite of loosely-coupled microservices. This provides you with a number of benefits. For example, you can replicate microservices across a cluster of VMs to improve fault tolerance. Should an individual VM fail, your application can fall back on other microservices in the cluster and continue to function. What’s more, microservices are easier to maintain, as you can patch or update the code and system environment of your containers without affecting others in your cluster.

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Containers and DevOps

The compact design of containers makes them highly portable. As a result, with the help of DevOps tools, such as Jenkins and CodeShip, they’re easy to incorporate into continuous integration (CI) and continuous delivery (CD) workflows. From a developer standpoint, containers are also highly practical, as they can be hosted on different servers with different configurations, provided that each server OS is using the same Linux kernel or, at least, one that’s compatible with the container environment. 

This allows coders to focus on code without needing to worry about the underlying infrastructure on which it will eventually run. Equally, developers can work collaboratively on projects regardless of the host environment each of them may be using.

Should You Use Docker?

Docker is one of several different container platforms. So, why would choose it over other container solutions? Well, first, Docker is, far and away, the most widely used container service. It's popularity rests squarely on the fact that it's a robust, secure, cost-effective, and feature-rich solution that's easier to deploy than any of its competitors. Second, it’s an open-source solution that's backed by a large community of companies and individuals who are continually contributing to the project. It offers strong support and a large ecosystem of complementary products, service partners, and third-party container images and integrations. Moreover, selecting Docker won't tie you to a specific vendor.

Finally, the Docker platform allows you to run its containers on Windows. This is made possible by a Linux virtualization layer, which sits between the Windows OS and the Docker runtime environment. In addition to Linux container environments, Docker for Windows also supports native Windows containers.

Although alternatives are now gradually maturing, when one looks across the container landscape, Docker still leads the way and remains the best choice for the majority of use cases. But before you decide whether Docker is right for you, here are the key concepts you’ll need to understand in advance of getting started with the Docker platform:

  • Docker Engine
    This is the application you install on your host machine to build, run, and manage Docker containers. As the core of the Docker system, it unites all of the platform's components in a single location.
  • Docker Daemon
    The workhorse of the Docker system, this component listens to and processes API requests to manage the various other aspects of your installation, such as images, containers, and storage volumes.
  • Docker Client
    This is the primary user interface for communicating with the Docker system. It accepts commands via the command-line interface (CLI) and sends them to the Docker daemon.
  • Docker Image
    A read-only template used for creating Docker containers. It consists of a series of layers that constitute an all-in-one package, which has all of the installations, dependencies, libraries, processes, and application code necessary to create a fully operational container environment.
  • Docker Container
    A living instance of a Docker image that runs an individual microservice or full application stack. When you launch a container, you add a top writable layer, known as a container layer, to the underlying layers of your Docker image. This is used to store any changes made to the container throughout its runtime.
  • Docker Registry
    A cataloging system for hosting, pushing, and pulling Docker images. You can use your own local registry or one of the many registry services hosted by third parties (e.g., Red Hat Quay, Amazon ECR, Google Container Registry, and the Docker Hub). A Docker registry organizes images into storage locations, known as repositories, where each repository contains different versions of a Docker image that share the same image name.

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With these fundamentals under your belt, let's take a brief look at several other aspects of Docker containers about which you should be aware:

  • Container Orchestration
    Once you’re ready to deploy an application to Docker, you’ll need a way to provision, configure, scale, and monitor your containers across your microservice architecture. Open-source orchestration systems, such as Kubernetes, Mesos, and Docker Swarm, can provide you with the tools you'll need to manage your container clusters. Typically, these are able to:
  • Allocate compute resources between containers
  • Add or remove containers in response to application workload
  • Manage interactions between containers
  • Monitor the health of containers
  • Balance the load between microservices
  • Cost and Performance Optimization
    Finally, you’ll need to optimize your deployments to ensure that you're getting the best performance and efficiency from your containers. Start by streamlining your containers as much as possible by packaging only what your application needs. This best practice also helps to minimize their attack surface and, thereby, improve security. And to assure that your containers are making the most efficient use of resources possible, you'll want to routinely monitor them to be certain that they're maintaining a good balance of CPU and memory allocation, cluster sizing, and replication of microservices. These steps are particularly important in cloud-based deployments because unnecessary resource consumption adds additional and unnecessary costs to your monthly cloud bills.

Learn more about Docker

 

Published: June 22, 2020

Last updated: Mar. 17, 2021