Docker vs. Kubernetes: 6 Key Differences and How to Choose
What Is Docker?
Docker is an open-source platform that automates the deployment, scaling, and management of applications by using containerization. Containers are lightweight, standalone, and executable packages that include everything needed to run a piece of software, including the code, runtime, system tools, system libraries, and settings.
The advantage of Docker is that it allows developers to package an application with all its dependencies into a standardized container that can run on any system. This eliminates the "it works on my machine" problem and ensures consistency across various development, testing, and production environments. Docker has gained popularity due to its efficiency, speed, and ease of use, becoming a de facto standard in the world of containerization.
However, Docker is not without its limitations. While it is useful for running containers on a single machine, it struggles to scale up and manage containers across multiple machines.
**Note: **The Docker platform provides an orchestration solution called Docker Swarm, which is comparable to Kubernetes. However, Docker Swarm is outside the scope of this article.
How Do Docker Containers Work?
Docker containers run instances of Docker images. Images are read-only templates with instructions for creating a Docker container. They are lightweight, as they share the machine’s OS system kernel, and don’t require an operating system of their own.
When a Docker image is launched using the docker run command, it becomes a Docker container. Docker uses a client-server architecture. The Docker client communicates with the Docker daemon, which is responsible for building, running, and managing Docker containers. The Docker client and daemon can run on the same host or communicate over a network.
While Docker containers are famous for their portability and ease of use, managing them at scale can be a challenge. Docker alone cannot handle the orchestration of containers across multiple machines. This is where the need for a container orchestration tool like Kubernetes arises.
What Is Kubernetes?
Kubernetes, also known as K8s, is an open-source platform designed to automate deploying, scaling, and managing containerized applications. It groups containers into units called pods for easier management and discovery. Kubernetes was originally designed by Google, based on their experience of running billions of containers, and is now maintained by the Cloud Native Computing Foundation.
Kubernetes addresses many of the scalability issues that Docker faces. It can manage and orchestrate containers not only on a single machine but across a cluster of machines, which Kubernetes calls nodes. Kubernetes also provides services such as load balancing, traffic routing, scaling, rolling updates, and secret management.
However, Kubernetes is more complex than Docker and has a steeper learning curve. It also requires more resources and a more complex setup than Docker, making it overkill for small-scale applications or simple deployments.
How Kubernetes Works
Kubernetes works by managing a cluster of machines and running containers on them. A Kubernetes cluster consists of a master node and multiple worker nodes.
The master node controls the worker nodes and the containers running on them. This is called the Kubernetes control plane, which comprises several components like the API Server, Scheduler, Controller Manager, and the etcd database that stores cluster state and configuration.
Each worker node runs a Kubelet, an agent that communicates with the master node. The worker node also runs Docker or another container runtime to run and manage containers.
Kubernetes uses a declarative configuration to manage the state of the cluster. You provide Kubernetes with the desired state of your system (the number of replicas of your app, network and disk resources to be allocated, etc.), and Kubernetes brings the current state to the desired state.
This is part of a series of articles about docker container.
Docker Container vs. Kubernetes: Key Differences
1. Orchestration
Docker is a platform that allows you to package an application and its dependencies into a container. It does offer basic orchestration features through Docker Swarm; these are much less powerful than Kubernetes but also easier to use.
On the other hand, Kubernetes is primarily an orchestration platform. It’s designed to manage clusters of containers across multiple servers, offering a high level of control and flexibility. It can handle complex, multi-container deployments and advanced enterprise requirements.
2. Resource Management
Docker manages resources at the container level, meaning each container has its own allocated resources. It provides an efficient way for managing the resources available on a single host and sharing it between containers running different applications.
Kubernetes manages resources at the pod level. A pod is a group of one or more containers that share the same network and storage resources. This approach allows for better resource utilization as resources can be shared and balanced across multiple containers within a pod. However, it does require a better understanding of how your applications and workloads are structured.
3. Networking
Docker uses a flat networking model, where each container has its own IP and there is full, free communication between containers. This is easy to understand and use but can lead to issues in larger or more complex deployments.
Kubernetes uses a networking model, where each pod has its own IP and containers within a pod share this IP. The basic networking model is often extended with open source add-ons like Calico or Flannel. Kubernetes can handle complex networking needs and offers better isolation and security, but it’s also more difficult to set up and manage.
4. Data Storage
In terms of data storage, Docker provides a simple and straightforward way to handle persistent data through volumes. These are directories that exist outside the container lifecycle and can be attached to containers to provide persistent storage.
Kubernetes provides a more comprehensive and flexible storage system. It supports simple volumes like Docker, but also introduces the concept of Persistent Volumes (PVs) and Persistent Volume Claims (PVCs). These allow for a more controlled and efficient handling of storage resources, especially in a multi-tenant environment.
5. Security
Docker, being a simpler platform, has fewer moving parts and thus potentially fewer security vulnerabilities. However, its flat networking model can be a security risk. Docker security risks are well understood and organizations like the Center for Internet Security (CIS) have released comprehensive benchmarks to help harden Docker containers against cyber threats.
Kubernetes has a more robust security model, with features like Role-Based Access Control (RBAC) and Security Contexts. However, many Kubernetes settings are not secure by default. Its complexity can also lead to security misconfigurations if not properly managed.
6. Cost and Complexity
Docker, as a simpler platform, is easier to learn and use, meaning that less tech-savvy employees can use it. It’s also typically cheaper to run, especially for smaller deployments.
Kubernetes offers greater scalability and flexibility, making it a better choice for larger, more complex deployments. However, it can be harder for less experienced employees to use and can be more expensive to run and manage, especially if you don’t have the necessary expertise in-house.
Related content: Read our guide to Kubernetes vs docker compose (coming soon)
Kubernetes vs. Docker: How to Choose?
If you’re just getting started with containerization and need a simple, easy-to-use platform, Docker might be the better choice.
If you’re dealing with complex, multi-container deployments and need a powerful orchestration platform, Kubernetes could be the way to go. Keep in mind, though, that Kubernetes’ complexity means it requires more knowledge and expertise to use effectively.
There is also a middle ground. There are several tools, including Acorn, that can help you easily set up and manage Kubernetes clusters without becoming cloud native experts.
Acorn: Running Kubernetes with the Ease of Docker
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