Docker - Kubernetes Architecture

Pre-requisite: Docker and Kubernetes

Docker and Kubernetes are two of the most popular tools in the field of containerization and cluster management, respectively. In this article, we will understand how Docker and Kubernetes work together to provide a seamless experience for developers and operators.

Docker is a tool that allows developers to package their applications and dependencies into lightweight, portable containers. These containers can then be shipped and deployed on any platform supporting Docker, making it easier to build, test, and deploy applications.

At a high level, Docker consists of three Main Components:

1. Docker Daemon
2. Docker Client
3. Docker Registry.

In other words, Docker allows developers to create a self-contained package that includes everything an application needs to run, including the code, libraries, dependencies, and runtime. This makes it easy to deploy the application on any Docker system, without worrying about differences in environment or dependencies.

Kubernetes, also known as K8s, is an open-source platform for automating containerized applications' deployment, scaling, and management. It was originally developed by Google and is now maintained by the Cloud Native Computing Foundation (CNCF).

Kubernetes uses a Master-Slave Architecture, with the Kubernetes master node responsible for managing the slave nodes (also called worker nodes) in the cluster. The master node consists of various components such as the API server, scheduler, and controller manager, which work together to manage the cluster. The slave nodes, on the other hand, are responsible for running the containerized applications. 

Kubernetes, on the other hand, allows developers to deploy and manage multiple containers at once. This is useful when an application is made up of multiple components, each of which is packaged in a separate container. Kubernetes can handle tasks such as scaling the number of containers up or down based on demand, rolling out updates to the containers, and ensuring that the containers are distributed evenly across a cluster of machines.

How Docker and Kubernetes Work Together

Docker and Kubernetes are often used together to Build, Deploy, and Manage modern applications. Here's how they work together in detail.

Packaging Applications into Containers

First, developers use Docker to package their applications into containers. A container is a self-contained, isolated environment that includes all the necessary code, libraries, and dependencies that an application needs to run. This makes it easy to deploy the application on any platform, as the container includes everything it needs to run in a single package.

Building and Testing Containers

Once the application is packaged into a container, developers can use Docker to build and test the container to ensure that it is working as expected. This can be done locally or in a continuous integration/continuous deployment (CI/CD) pipeline, where containers are built and tested automatically as code changes are made.

Deploying Containers to a Cluster

Once the containers are built and tested, they can be deployed to a cluster of servers using Kubernetes. A cluster is a group of servers that are used to run containerized applications. Kubernetes helps to automate the deployment, scaling, and management of these containers across the cluster.

Managing Containers with Kubernetes

When containers are deployed to a cluster using Kubernetes, they can be easily scaled up or down to meet changing demand. Kubernetes also helps to ensure the availability and reliability of the containers, automatically rescheduling them if they fail or become unavailable.

Working Scenario Steps

1. A Developer creates a new application and writes the code for it.
2. The developer creates a Dockerfile, which is a set of instructions for building a Docker container. The Dockerfile specifies things like the base image to use, the dependencies to install, and any other requirements for running the application.
3. The Developer builds the Docker container using the Dockerfile. This creates a self-contained package that includes everything the application needs to run.
4. The Developer tests the Docker container locally to ensure that it is working as expected.
5. The Developer pushes the Docker container to a registry, such as Docker Hub, where it can be accessed by other users.
6. The Developer creates a Kubernetes deployment configuration file, which specifies things like the number of replicas of the container to run and any other details about how the containers should be deployed.
7. The Developer uses the Kubernetes command-line interface to deploy the Docker containers to a cluster of machines.
8. Kubernetes takes care of tasks such as scaling the number of containers up or down based on demand, rolling out updates to the containers, and ensuring that the containers are distributed evenly across the cluster.

In summary, Docker and Kubernetes work together to make it easier for developers to build, test, and deploy their applications in a consistent and reliable way. By packaging applications into containers and using Kubernetes to manage their deployment and scaling, developers can streamline their workflows and improve the efficiency and effectiveness of their development process.