Docker on Kubernetes (K8s): A Powerful Combo for Scalable Containerized Applications

Docker on Kubernetes (Docker on K8s)

Kubernetes (K8s) and Docker are often paired in modern containerized applications. Docker is a containerization platform that allows developers to package applications and their dependencies into containers, ensuring that applications operate consistently in different environments. Kubernetes, on the other hand, is a container orchestration platform that automatically deploys, scales, and manages containerized applications. Together, Docker and Kubernetes provide a powerful combination for running decentralized applications at scale.

1. What is Kubernetes?

Kubernetes (K8s) is an open source platform that helps manage, scale, and deploy containerized applications. It was originally developed by Google and is now maintained by the Cloud Native Computing Foundation (CNCF). Kubernetes abstracts the underlying infrastructure and provides a unified platform to deploy and manage applications in a variety of environments—on-premises, in the cloud, or hybrid.

Kubernetes provides the following capabilities:

• Container orchestration: Kubernetes automates the deployment, scaling, and management of containerized applications.
• Self-healing: Kubernetes can automatically replace failed or unresponsive containers.
• Scalability: Kubernetes makes it easy to scale applications horizontally by adding or removing container instances as needed.
• load balancing: Kubernetes can automatically distribute traffic across containers to ensure that application traffic is balanced and no single container is overwhelmed.
• Declarative configuration: Kubernetes allows you to define the desired state of your application (for example, how many replicas of a container you want), and Kubernetes will automatically manage the state to conform to that configuration.

2. How Docker integrates with Kubernetes

Kubernetes is an orchestration platform, and Docker is a container runtime. Docker packages applications and their dependencies into container images, and Kubernetes deploys and manages these containers. Docker is commonly used to build container images that are then run and orchestrated by Kubernetes.

Key components of Docker and Kubernetes:

1. Docker container: Docker is used to build and run containers, which are lightweight, isolated, and portable environments that encapsulate applications and their dependencies.
2. Docker image: Docker images are templates for building containers. They contain everything needed to run the application, such as application code, system libraries, and dependencies.
3. Kubernetes Pod: In Kubernetes, containers are divided into pod. A Pod can contain one or more containers, and the containers in a Pod share the network, storage, and life cycle.
4. Kubernetes nodes: These are machines (virtual or physical) that run containerized applications. Kubernetes nodes are where Docker containers execute.

Kubernetes can use different container execution times (such as Docker, containerd, or CRI-O), but Docker remains one of the most popular execution times, especially for development and testing.

3. Execute Docker containers on Kubernetes

To execute a Docker container on Kubernetes, you need to perform the following steps:

1. Build Docker image: The first step is to create a Docker image for your application. The image contains the application code, libraries, dependencies, and runtime required to run the application in the container.

example Dockerfile:

   FROM node:14

   WORKDIR /app

   COPY package.json /app

   RUN npm install

   COPY . /app

   CMD ["node", "server.js"]

You can build a Docker image using the following command:

   docker build -t my-app .

1. Push the Docker image to the registry: After the image is built, you need to push it to a container registry, such as Docker Hub, Amazon ECR, or Google Container Registry (GCR).

example:

   docker push my-app:latest

1. Deploy Docker images on Kubernetes: After you push the Docker image to the registry, you can create a Kubernetes deployment profile (YAML) that specifies how Kubernetes should execute the Docker container.

example deployment.yaml For Kubernetes deployment:

   apiVersion: apps/v1
   kind: Deployment
   metadata:
     name: my-app-deployment
   spec:
     replicas: 3
     selector:
       matchLabels:
         app: my-app
     template:
       metadata:
         labels:
           app: my-app
       spec:
         containers:
         - name: my-app
           image: my-app:latest
           ports:
           - containerPort: 8080

Deploy it to Kubernetes using the following command:

   kubectl apply -f deployment.yaml

This will set up a deployment with 3 replicas my-app Containers run in a Kubernetes cluster.

1. Exposing applications using services: You can use Kubernetes services to expose your applications to the outside world. This service provides stable IP and DNS names that can be used to access your applications.

example service.yaml:

   apiVersion: v1
   kind: Service
   metadata:
     name: my-app-service
   spec:
     selector:
       app: my-app
     ports:
       - protocol: TCP
         port: 80
         targetPort: 8080
     type: LoadBalancer

Application service:

   kubectl apply -f service.yaml

4. Advantages of using Docker with Kubernetes

• portability: Docker containers are portable, which means you can move them seamlessly between different environments (development, staging, and production) and between different cloud providers. Kubernetes lets you deploy these containers in a unified way.

• Scalability: Kubernetes lets you scale Docker containers based on the level of demand. Kubernetes can automatically increase or decrease the number of running containers based on load, ensuring high availability and optimal resource usage.

• automation: Kubernetes automates the deployment, scaling, and management of Docker containers. With features like self-healing, rolling updates, and auto-scaling, Kubernetes simplifies container management at scale.

• isolation: Docker provides isolation between containers, and Kubernetes further enhances this by isolating Pods and efficiently managing resources.

• Declarative management: Kubernetes allows you to declare the desired state of your application (e.g. number of replicas, resource limits) in a configuration file (YAML). Kubernetes will work to maintain this state, automatically handling failures or resource adjustments.

5. Kubernetes and Docker Swarm

While Docker Swarm is Docker’s native orchestration tool, Kubernetes offers more powerful capabilities and is widely considered the industry standard for container orchestration. Their comparison is as follows:

Docker Swarm is easier to set up and suitable for smaller environments, while Kubernetes is more powerful, scalable and suitable for large-scale production environments.

6. Conclusion

Together, Docker and Kubernetes form a powerful toolset for managing containerized applications at scale. Docker simplifies the process of packaging applications into containers, and Kubernetes provides the orchestration to deploy, scale, and manage these containers in production environments. Whether you are developing a small project or a large microservices architecture, using Docker with Kubernetes will increase the flexibility, portability and scalability of your applications.