The Differences Between Kubernetes and Docker

Kubernetes is a platform for automating the deployment, scaling and orchestration of containers, whereas Docker is a technology for creating and running containers. Still not sure what the difference is? That is understandable, the two terms are very often confused – including by IT professionals and companies. Although both tools allow you to run applications in Linux containers, they work at very different levels of the stack and offer complementary features. Read this article to understand the differences between Kubernetes and Docker and how they can work together.

What is Kubernetes?

The Kubernetes lexicon

Before diving into the concrete functioning of Kubernetes, it is important to define a few key terms. This open source container orchestration platform offered by Google is based on:

1.    Containers

Containers are standardised executable components that combine the application’s source code with the operating system’s libraries. Each container is isolated from other processes and is run on a computer, a physical server or a virtual machine (VM).

2.    Nodes

A Kubernetes node is a small collection of resources that supports one or more containers. These nodes are actually machines (virtual or physical) in which the containers will be deployed. Each node integrates a kube-proxy and kubelet; services that help create the execution environment and support the Kubernetes pods.

3.    Pods

The pod is the smallest deployable unit in a Kubernetes environment. Each pod has one or more containers running in tandem that share networking and storage resources common to the host node where they reside.

4.    The Kube-proxy

As its name implies, the kube-proxy is a network proxy that runs on each node in the cluster. The kube-proxy maintains the network rules on the nodes and thus enables network communication both inside and outside a Kubernetes cluster.

For this purpose, the kube-proxy uses the packet filtering layer of the operating system or forwards the network traffic itself.

5.    Clusters 

A Kubernetes cluster represents a set or collection of nodes (machines) that run containerised applications. It means that they bundle an application and its required services and dependencies into a package.

6.    The Kubelet

The Kubelet ensures that the containers described in the PodSpecs work. Specifically, it registers Kubernetes nodes with the API server and ensures that all containers in a pod are running and “healthy”. It then reports back to the master node on the health of its host and transmits information to and from the API server.

How Kubernetes works

Kubernetes groups containers that support a single microservice or application into a pod. Within each pod, there are one or more containers that execute the business logic. Each pod is then exposed to the network through another Kubernetes abstraction called service.

The containers, pods and services, are hosted within nodes (real computers or virtual machines).

Kubernetes will orchestrate these containers to support the deployment, management and load management of a system. It allows to:

●      design application services that are split across multiple containers;

●      schedule containers in clusters;

●      manage the organisation, networking and scaling of containers;

●       guarantee the integrity of containers and clusters.

In concrete terms, Kubernetes will allow the developer to focus on the business side by taking care of the adaptation of the back-end structure and monitoring. For example, with Kubernetes, if a node A is unresponsive, the pods deployed on that node will automatically be transferred to another node to ensure stability. This makes Kubernetes deployments scalable, versatile and resilient in the event of failure.

However, to create and launch containers, Kubernetes needs a different software. This is where Docker comes in

What is Docker?

The components of Docker

Docker is a technology used to create, run and manage the life cycle of software containers. Each container contains one or more processes, organised under a single name and unique identifier.

The Docker program has two main components:

●      a client Command Line Interface (CLI) tool to execute instructions to the Docker runtime environment on the command line;

●      a container runtime environment to create and run the container on the operating system.

The other major components are:

Docker Engine

Docker Engine is an application to be installed on the host computer or server to create, run and manage Docker containers in a client-server environment.

It is this engine that links the different components together.

Docker Client

The Docker Client is the command interface that receives instructions for communicating with the Docker system.

Dockerfile

The aptly named Dockerfile is a file present in each Docker container. It contains the instructions for creating a Docker image and specifies in particular:

●      the operating system on which the container will be based;

●      the programming language used;

●      environmental variables (network ports, file locations, etc.).

Docker images

The images are models, accessible in read-only mode, which allow the containers to be created. These models are comprised of several layers that integrate installations, libraries, dependencies and operational code.

Docker containers

For Docker, containers are instances of an image or model that will be executed on a physical or virtual machine. A Docker container can be run on a microservice or on a complete application stack.

The uses of Docker

Docker will therefore allow developers to package applications in containers and then run them. This technology is very popular in DevOps approaches and in hybrid multi-cloud environments.

It is also recommended to use Docker in architectures that rely on microservices and for applications that do not necessarily need a graphical interface.

Docker will speed up the deployment of applications. However, to run them, Docker will use containers that may fail. Kubernetes, with its container restart feature, will remove those that no longer match and shift the load to others.

Similarly, Docker will manage the security of applications, but it is Kubernetes that optimises storage by allowing users to automatically mount the appropriate storage system.

Kubernetes and Docker are therefore fundamentally distinct in their goals and functionalities. Docker is a technology for defining and running containers. Kubernetes is a container orchestration framework that manages and monitors previously defined and launched containers. The differences between Kubernetes and Docker make these technologies complementary and they are often used together in IT projects.

Have you already worked with Kubernetes and Docker? Feel free to give us feedback on the IT forum!

Sources and useful links:

• Official Kubernetes documentation: https://kubernetes.io/fr/docs/concepts/overview/components

• Official Docker documentation: https://docs.docker.com/