Docker and Kubernetes are both popular tools in the world of containerization, but they serve different purposes and operate at different levels of the container ecosystem. Here’s a breakdown of the key differences between Docker and Kubernetes:

1. Basic Definition

• Docker: A platform that allows developers to build, ship, and run containers. It focuses on containerizing individual applications, making them portable and consistent across different environments.
• Kubernetes: A container orchestration platform that automates the deployment, scaling, and management of containerized applications across a cluster of machines.

2. Core Purpose

• Docker: Handles creating and running containers on a single host. It's primarily used for container runtime, image creation, and storage.
• Kubernetes: Manages containerized applications across a distributed system of nodes (multiple Docker hosts). It orchestrates container deployment, scaling, load balancing, and high availability.

3. Scope

• Docker: Deals with container runtime, packaging, and image management. Docker runs containers, while its additional tools (e.g., Docker Compose) help with basic orchestration and multi-container setups on a single host.
• Kubernetes: Manages clusters of containers across multiple hosts, providing a framework for scheduling containers (called Pods), service discovery, auto-scaling, rolling updates, and self-healing of containers.

4. Components

• Docker:
  • Docker Engine: The core tool that runs containers.
  • Docker Hub: Central repository for Docker images.
  • Docker Compose: A tool for defining and running multi-container Docker applications in a single environment.
• Kubernetes:
  • Master Node: Coordinates the cluster with components like the API server, controller manager, and scheduler.
  • Worker Nodes: Hosts that run the application workloads (Pods).
  • Kubelet: An agent on each worker node that communicates with the master.
  • etcd: Distributed key-value store for cluster state management.
  • Kube Proxy: Handles networking for services in Kubernetes.

5. Orchestration

• Docker: Basic orchestration can be achieved using Docker Swarm or Docker Compose. Swarm mode allows clustering of Docker nodes, but it is simpler and less feature-rich compared to Kubernetes.
• Kubernetes: Provides robust orchestration capabilities. It allows automatic scheduling, service discovery, self-healing, load balancing, rolling updates, and scaling across multiple nodes.

6. Scaling

• Docker: Scaling requires the use of Docker Swarm or third-party tools. Docker Compose can scale containers but is limited to a single host.
• Kubernetes: Built-in auto-scaling capabilities. It can scale applications horizontally across clusters of machines by increasing or decreasing the number of Pods based on metrics such as CPU usage.

7. Load Balancing

• Docker: Load balancing can be achieved using Docker Swarm, which has built-in support for load balancing across containers. Docker Compose does not offer built-in load balancing.
• Kubernetes: Kubernetes provides a more advanced service load balancing solution. It can automatically distribute traffic between containers (Pods) and uses an internal DNS to facilitate service discovery.

8. Networking

• Docker: Networking in Docker can be configured using drivers like bridge, host, overlay, and others. In Docker Swarm, overlay networks allow communication between containers across different hosts.
• Kubernetes: Kubernetes has a more sophisticated networking model where every Pod gets its own IP address. Kubernetes also supports network policies for managing communication between Pods and services.

9. Self-Healing

• Docker: Docker Swarm can restart containers if they crash, but the functionality is not as comprehensive as Kubernetes.
• Kubernetes: Automatically monitors containers and nodes, restarting failed containers, replacing them if they are unhealthy, and rescheduling containers on different nodes if necessary.

10. Storage Management

• Docker: Offers storage using volumes and bind mounts to persist data. Docker volumes are container-agnostic, making them easy to share between containers.
• Kubernetes: Supports more advanced storage options. Kubernetes allows dynamic provisioning and management of storage using Persistent Volumes (PVs) and Persistent Volume Claims (PVCs). It also integrates with various storage systems like AWS EBS, GCE Persistent Disk, NFS, and more.

11. Deployment & Updates

• Docker: With Docker Compose or Docker Swarm, containers can be updated, but rolling updates and rollback features are limited.
• Kubernetes: Offers advanced deployment strategies like rolling updates, blue-green deployments, and canary deployments out-of-the-box. Kubernetes also supports rollback functionality in case of failures.

12. Ecosystem

• Docker: Focuses primarily on container lifecycle management (building, shipping, and running containers). Docker Hub, Docker Compose, and Docker Swarm are part of the Docker ecosystem.
• Kubernetes: Kubernetes is part of a broader cloud-native ecosystem and integrates well with other CNCF (Cloud Native Computing Foundation) tools like Helm (for managing applications), Prometheus (for monitoring), Istio (for service mesh), and more.

13. Learning Curve

• Docker: Easier to learn and use for basic containerization and orchestration needs, especially on single-node setups.
• Kubernetes: More complex due to its broad feature set, but necessary for advanced container orchestration in large-scale, multi-node environments.

14. Community and Support

• Docker: Strong community support, especially around Docker Hub and Docker Compose. Docker Swarm is less popular compared to Kubernetes.
• Kubernetes: Massive community support with a large ecosystem of tools and libraries. It has become the de facto standard for container orchestration.

Summary Table

Real-World Usage

• Docker: Ideal for local development and for small-scale projects where you need to run containers on a single server or a few servers.
• Kubernetes: Preferred for large-scale, production-grade environments where you need to manage many containers across multiple hosts with advanced features like auto-scaling, load balancing, and self-healing.

In practice, Docker and Kubernetes are often used together: Docker to build and package containers, and Kubernetes to orchestrate and manage them in a distributed environment.