Kubernetes VS Docker: What‘s the Difference? Explained With Examples

If you‘re a developer or work in the software industry today, there‘s a very good chance you‘ve heard of Docker and Kubernetes. These two technologies have revolutionized the way we build, package, deploy, and operate applications in the era of cloud computing and microservices. But what exactly are Docker and Kubernetes, and how do they differ? In this in-depth article, we‘ll break it all down from the perspective of a full-stack developer.

The Evolution of Application Deployment

To appreciate the significance of Docker and Kubernetes, it‘s useful to understand the evolution of application deployment. Traditionally, applications were built to run on specific physical servers. This meant that development and operations teams had to carefully coordinate the specific hardware, operating system, libraries, and other dependencies required by the application. Deployments were often manual, error-prone, and difficult to scale.

As virtualization became more widespread, applications could be packaged along with their dependencies into virtual machines (VMs). This made deployments more portable and allowed better utilization of physical server resources. However, VMs are relatively heavyweight, slow to start up, and still tie the application to a specific guest OS and virtualization platform.

Containers emerged as the next evolution, providing a more lightweight and portable way to package and run applications. Containers provide process and resource isolation similar to VMs, but share the host machine‘s operating system kernel. This makes them much more efficient than VMs.

The Rise of Docker

Docker, first released in 2013, has become synonymous with containers and is the most widely used container platform today. Docker provides a standard format for packaging an application and its dependencies into a container image that can run consistently on any platform that supports Docker.

Using Docker, developers can define a repeatable build process for their application that captures all its dependencies in a Dockerfile. This Dockerfile specifies the base operating system, runtime environment, libraries, configuration files, and other components needed by the application. Docker then builds this into a portable container image.

FROM node:14

WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .

EXPOSE 3000
CMD ["npm", "start"]

Example Dockerfile for a Node.js application

Docker containers can be started, stopped, and destroyed quickly, making them ideal for dynamic environments. Containers also provide a high degree of isolation, ensuring that applications don‘t interfere with each other or with the host system.

Docker has seen explosive adoption and has become a fundamental building block for modern cloud-native application development. As of 2021, Docker reported over 13 million developers using its platform, over 13 billion image pulls per month from Docker Hub, and over 7.3 million applications running on Docker.[^1]

The Need for Container Orchestration

While Docker provides the fundamental building blocks for containerization, running containers in production at scale introduces additional challenges. You need to consider things like:

• How do you manage and schedule containers across a cluster of machines?
• How do you scale the number of containers up or down based on demand?
• How do you handle container failures and ensure the right number are always running?
• How do you route traffic to the appropriate containers?
• How do you roll out application updates without downtime?

This is where container orchestration platforms like Kubernetes come in.

The Rise of Kubernetes

Kubernetes (often abbreviated as K8s) is an open-source system for automating the deployment, scaling, and management of containerized applications. It was originally developed by Google, drawing from their experience running billions of containers per week, and is now maintained by the Cloud Native Computing Foundation (CNCF).

Kubernetes provides a declarative way to define the desired state of your application deployment. You specify things like how many replicas of a container you want running, what resources they require, and how they should be updated. Kubernetes then continuously works to ensure that the actual state of your cluster matches your desired state.

Here‘s a simple example of a Kubernetes deployment YAML file:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
spec:
  selector:
    matchLabels:
      app: nginx
  replicas: 2
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.14.2
        ports:
        - containerPort: 80

This defines a deployment that ensures two replicas of the nginx container are always running.

Some of the key features of Kubernetes include:

• Automatic bin packing: Kubernetes automatically schedules containers based on their resource requirements and constraints.
• Self-healing: Kubernetes restarts containers that fail, replaces containers, kills containers that don‘t respond to health checks, and doesn‘t advertise them to clients until they are ready.
• Horizontal scaling: Kubernetes can automatically scale your application up and down based on CPU utilization or other metrics.
• Service discovery and load balancing: Kubernetes can expose a container using a DNS name and automatically load balance traffic across a set of containers.
• Automated rollouts and rollbacks: Kubernetes progressively rolls out application changes while monitoring application health to ensure there‘s no downtime. It can also automatically roll back changes if something goes wrong.
• Secret and configuration management: Kubernetes lets you store and manage sensitive information like passwords and OAuth tokens, and provides ways to inject configuration into containers at runtime.

Kubernetes has seen massive adoption and has become the de facto standard for container orchestration. According to the CNCF‘s 2021 survey, 96% of organizations are either using or evaluating Kubernetes.[^2] The Kubernetes ecosystem has also exploded, with over 600 platforms and products integrating with Kubernetes in some way.[^3]

Key Differences Between Docker and Kubernetes

While Docker and Kubernetes are both key components of the modern cloud-native stack, they serve different purposes and operate at different layers of abstraction.

Scope

• Docker is a platform for developing, shipping, and running containers. It‘s focused on the packaging and runtime of individual containers.
• Kubernetes is a platform for orchestrating and managing clusters of containers. It‘s focused on the deployment, scaling, and operation of container-based applications.

Scheduling and Orchestration

• Docker provides basic container scheduling via Docker Swarm, but it‘s not as feature-rich as Kubernetes.
• Kubernetes provides advanced scheduling, including automatic bin packing, horizontal scaling, self-healing, and rolling updates.

Networking

• Docker provides basic container-to-container networking and the ability to map ports from the host to the container.
• Kubernetes provides more advanced networking features, including DNS-based service discovery, load balancing, and ingress control.

Configuration Management

• With Docker, application configuration is typically baked into the container image or injected via environment variables.
• Kubernetes provides more robust configuration management via ConfigMaps and Secrets, which can be updated independently of the container images.

Storage

• Docker provides volume drivers for mapping host directories into containers or creating dedicated volumes.
• Kubernetes provides abstractions like PersistentVolumes and PersistentVolumeClaims to decouple storage from pods and enable automatic provisioning of storage resources.

Ecosystem and Tooling

• Docker has a large ecosystem of tools for building, sharing, and running containers, with Docker Hub as a central repository for container images.
• The Kubernetes ecosystem is even larger, with a wide range of tools for packaging (Helm), monitoring (Prometheus), logging (Fluentd), tracing (Jaeger), and more, as well as integrations with most major cloud providers.

Using Docker and Kubernetes Together

In practice, Docker and Kubernetes are often used together, with Docker providing the container packaging and runtime, and Kubernetes providing the orchestration and management layer.

A typical workflow might look like this:

1. Developers write code and create a Dockerfile that defines how to build a container image for their application.
2. CI/CD pipelines use Docker to build, test, and push container images to a registry like Docker Hub or Google Container Registry.
3. Kubernetes manifests (written in YAML or JSON) define the desired state of the application deployment, specifying which container images to use, how many replicas to run, what resources they require, and how they should be updated.
4. Kubernetes pulls the necessary container images from the registry and schedules them to run on available nodes in the cluster, continuously monitoring and adjusting to maintain the desired state.

This combination of Docker for packaging and Kubernetes for orchestration has become a standard pattern for deploying and operating applications in the cloud.

As Kelsey Hightower, a prominent Kubernetes advocate, put it: "Kubernetes does not replace Docker, but it does replace some of the higher-level technologies that were previously built on top of Docker, such as Docker Swarm or Apache Mesos. Kubernetes is more of a replacement for those higher level orchestration technologies, but it still benefits from the portable container image that Docker provides." [^4]

Best Practices for Using Docker and Kubernetes

While Docker and Kubernetes provide powerful capabilities, using them effectively requires following certain best practices:

• Use small, focused containers: Each container should run a single process and be as small as possible. This makes them more reusable, easier to update, and faster to start up.
• Make containers stateless where possible: Containers should be treated as disposable and not store persistent state inside the container. Use Kubernetes volumes or external databases for persistence.
• Use declarative configurations: Define your application deployment declaratively using Kubernetes YAML files, and let Kubernetes handle the details of making the actual state match the desired state.
• Implement health checks: Provide health check endpoints for your containers so that Kubernetes can determine if they‘re running properly and automatically restart them if not.
• Follow the principle of least privilege: Give containers only the permissions and resources they need to function. Use Kubernetes RBAC, network policies, and pod security policies to enforce security boundaries.
• Implement CI/CD pipelines: Automate your build, test, and deployment process using CI/CD pipelines that build Docker images and deploy them to Kubernetes.
• Monitor and log everything: Use tools like Prometheus, Grafana, and the Elastic Stack to monitor your Kubernetes clusters and applications. Log all relevant events and aggregate logs for easy querying.

The Future of Containers and Orchestration

The Docker and Kubernetes story is still being written, but the future looks bright for these technologies and the cloud-native approach they enable.

Some emerging trends and areas of innovation include:

• Serverless platforms like Knative that use Kubernetes as a foundation for running serverless workloads
• Service meshes like Istio and Linkerd that provide advanced traffic management, security, and observability for microservices
• GitOps approaches that use Git as the single source of truth for declarative infrastructure and applications
• Edge computing use cases that leverage Kubernetes‘ portability and scalability to deploy applications across distributed edge environments
• WebAssembly integration that allows running WebAssembly modules in Kubernetes for improved performance and isolation

As Alexis Richardson, CEO of Weaveworks, predicts: "In the next five years, Kubernetes will become the TCP/IP of the cloud. It will be so ubiquitous, so widely deployed, and so mature that you can depend on it always being there, and always working." [^5]

Conclusion

Docker and Kubernetes are two of the most important technologies in the world of modern, cloud-native application development. While they serve different purposes, they complement each other and are often used together.

Docker provides the standard format for packaging applications into portable, lightweight containers. Kubernetes provides the orchestration layer for deploying, scaling, and managing those containers across a cluster.

For developers, understanding how to use Docker and Kubernetes effectively is becoming an essential skill. By adopting a container-based, microservices-oriented approach and leveraging the rich ecosystem of cloud-native tools, developers can build applications that are more scalable, resilient, and agile.

The combination of Docker and Kubernetes is a powerful foundation for the future of application development and deployment. As the ecosystem continues to evolve and mature, it‘s an exciting time to be a developer in the world of containers and orchestration.

[^1]: Docker Company Fact Sheet (2021)
[^2]: CNCF Survey 2021
[^3]: Kubernetes Certified Solutions Landscape
[^4]: "What is the role of Docker in a Kubernetes world?" – The New Stack
[^5]: "The Future of Kubernetes and Containers" – The New Stack