What are Docker and containers?

Docker and containers: definition

The image comes from logistics: just as a shipping container fits on any ship, train, or truck regardless of its contents, a software container runs on a developer's laptop just as it does on the test server or in the cloud. The phrase “But it works on my machine” loses its terror.

Docker was released in 2013 and made container technology practical for development teams' everyday work. Today, it is a standard tool in development and operations.

How containers work

Unlike a virtual machine, a container doesn't come with its own operating system but shares the kernel of the host system. This makes containers lightweight: they start in seconds and require few resources.

To run many containers across multiple servers, orchestration tools such as Kubernetes are used. They distribute the load, restart crashed containers, and scale as needed.

• Dockerfile: build instructions describing what goes into the container
• Image: an immutable template from which containers are started
• Container: a running instance of an image
• Registry: storage for images, e.g., Docker Hub
• Docker Compose: starts several related containers together

Benefits and limitations of containers

Containers ensure identical environments from development to the live system. New team members can start a project with a single command, deployments become reproducible, and different applications with different versions run side by side without problems.

However, containers also add complexity: images must be kept up to date so that no outdated, insecure libraries are in use. Data that needs to persist requires its own storage volumes. And Kubernetes is often overkill for small projects.

• The same environment from development to production
• Fast startup, low resource requirements
• Combines well with CI/CD and cloud hosting
• Update images and dependencies regularly

Real-world example: containers for an application that has grown over time

A company runs an internal web application that only works properly on a specific, now outdated server. Once the application, along with its database and background services, is packaged into containers, it can be moved to modern infrastructure, tested locally, and integrated into a CI/CD pipeline. At the same time, the Dockerfile documents what the application needs in order to run—knowledge that previously often existed only in a few people's heads.

Nano Concepts containerizes existing and new applications, sets up the right runtime environment, and deliberately chooses only as much infrastructure as necessary—from a single server with Docker Compose to a Kubernetes environment.