For several years now, the IT world has been undergoing a profound transformation in how applications are developed and deployed. With the rise of microservices, DevOps, and the cloud, we talk less about “servers” and “virtual machines,” and more about “containers,” automation, and scalability. In this new landscape, two technologies keep coming up: Docker and Kubernetes.
Docker democratized containerization, making application creation and deployment simpler, faster, and reproducible. Kubernetes made it possible to scale by orchestrating hundreds, even thousands, of containers in an automated and resilient way.
In this article, we explain what these two technologies are and how they complement each other.
Docker: Simplified Containerization
Recap: What Is a Container?
A container is a lightweight, portable unit that packages everything needed to run an application: code, libraries and dependencies, configuration files, and so on. Unlike virtual machines (VMs), containers share the host OS kernel, which makes them much lighter and faster to start.
Docker: Description and Role
Docker is an open source platform that makes it easy to create, package, deploy, and run containers. Using configuration files called Dockerfiles, you can define a complete application environment in just a few lines of code. The Docker engine then builds an image, which can be run as one or more containers.
Docker: The Benefits
Portability: Docker images run identically across different environments (dev, test, staging, production);
Isolation: each container runs in isolation, avoiding conflicts between applications (note, however, that this isolation is weaker than with virtual machines);
Reproducibility: the environment is defined in code, which guarantees reproducible deployments;
Collaborative and easy image distribution: images can be stored and shared via registries (e.g., the well-known Docker Hub)
A Classic Container Development Use Case:
A developer can build a Docker image of their web application, test it locally, and then push it to a test or production environment without having to reconfigure the operating system or dependencies.
Kubernetes: Container Orchestration at Scale
While Docker makes it easy to launch one or more containers, it doesn’t provide all the tools needed to manage a large number of containers across a distributed cluster. As an application starts to grow, running across multiple machines with multiple services, instances, and environments, manual container management quickly hits its limits. This is the context in which Kubernetes becomes indispensable.
What Is Kubernetes?
Kubernetes (or “K8s”) is an open source container orchestration platform originally developed by Google. Kubernetes lets you deploy, manage, scale, and monitor containerized applications in an automated, intelligent way.
Kubernetes doesn’t just finely distribute load across multiple services — it also automatically restarts failed components, deploys updates without downtime, and guarantees service continuity, even when a node goes down. Kubernetes acts like a conductor: it makes sure every container is in the right place, healthy, and interacting correctly with the rest of the environment.
Kubernetes relies on a declarative model: you describe the desired state of the system, and the engine ensures it stays that way.
To learn more (its history, architecture, how it relates to infrastructure components, etc.), check out our detailed article on Kubernetes.
Kubernetes: Key Concepts
Pods: the basic unit in Kubernetes — a pod can contain one or more containers sharing the same network and storage.
Services: a network entry point for accessing one or more pods, even as they change.
Deployments: objects that describe the desired number of pods and manage automatic updates.
Cluster: a set of nodes (physical or virtual machines) orchestrated by Kubernetes.
Kubernetes: The Main Benefits
Resilience: automatic container restart in case of a crash.
Scalability: dynamic adjustment of the number of pods based on load.
Rolling updates: gradual updates with no service interruption.
Auto-healing: automatic detection and replacement of failed components.
We’ve written a detailed article on the business benefits and challenges to anticipate with Kubernetes.
Docker and Kubernetes: How They Complement Each Other
How Docker and Kubernetes Work Together
Docker and Kubernetes are built to work together. Docker is the go-to tool for building containers, while Kubernetes orchestrates their execution at scale.
For a long time, Kubernetes used Docker as its container runtime. Since version 1.20, Kubernetes has migrated to containerd, a lighter runtime directly integrated into the Cloud Native ecosystem. This technical shift doesn’t call into question Docker’s usefulness in modern workflows.
Today, Docker is mainly used for the build: it lets you create reliable, consistent images. Kubernetes then takes over for the run: it schedules, deploys, monitors, and maintains these containers in production. This is a natural separation of roles that promotes smooth collaboration between development and operations.
A Simplified Workflow for a Containerized App: From Build to Run
a) A developer writes an application and creates a Dockerfile to containerize it;
b) A continuous integration (CI) pipeline, such as GitLab CI or GitHub Actions, builds a Docker image and pushes it to a registry (Docker Hub, Quay, Harbor, etc.);
c) Kubernetes configuration files (YAML manifests) define how this image should be deployed in the cluster;
d) Kubernetes automatically orchestrates the deployment, handling load distribution and restarts. It also facilitates rolling updates.
e) The application is also monitored using modern cloud native monitoring and metrics technologies (Prometheus, Thanos, Grafana).
Even though it’s not always relevant to move applications to containers (significant legacy constraints, little benefit for the application in moving to a complex Kubernetes-driven infrastructure, etc.), this application development workflow has today become a standard in modern architectures.
Conclusion
Docker and Kubernetes are two pillars of modern infrastructure. Docker revolutionized the way applications are packaged and deployed through containerization. Kubernetes makes it possible to harness this power at scale, bringing automation, resilience, and scalability.
These technologies complement each other, and mastering them is an essential foundation for adopting effective DevOps practices, building Cloud Native architectures, and making deployments more reliable.
At Enix, we help our clients set up and operate Kubernetes platforms around the clock, across any type of cloud environment (private, public) or on-premises, with a tailored approach. We also offer Docker and Kubernetes training, highly popular in France and delivered by our co-founder Jérôme Petazzoni, who is also one of the creators of Docker.
Don’t hesitate to contact us to discuss your projects!
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