How many times have you heard the phrase: „It works for me”? In the world of programming, differences in environments between the developer's computer and the production server are the most common cause of errors. The solution, which in 2026 is the absolute standard in the IT industry, is containerisation. If you want to find out, what is docker and how to use containers, to eliminate environment configuration problems once and for all, this article is for you.
What is Docker and why has it changed the rules of the game?
Docker is an open-source platform that allows an application with all its dependencies (libraries, configuration files, specific runtime version) to be packaged into a single, lightweight unit called a container. Unlike traditional virtualisation, containers do not need their own operating system - they share a system kernel with the host, making them much faster and less resource-intensive.
Basic concepts you need to know:
- Image (Image): This is a static file (template) that contains the code for your application and instructions on how to run it. You can think of it as a „recipe” for your application.
- Container: It is a running instance of an image. It is the „live” process in which your application is running.
- Registry(s): A place where images are stored. The most popular of these is Docker Hub - image registry.
How do I get started with Docker? Dockerfile in practice
The first step to containerisation is to create a file Dockerfile. This is a text file containing a sequence of commands that Docker executes to build an image of your application.
For Node.js applications, this process typically involves:
- Selection of a base image (e.g.
node:20-alpine). - Setting up the working directory.
- Copying files
package.jsonand installation of dependencies. - Copy the rest of the source code.
- Specifying a start command (e.g.
npm start).
In order to optimise efficiency in production, experts are using so-called 'efficiency-boosters'. multi-stage builds. This allows you to use one image to compile your code (e.g. TypeScript) and then copy only the finished result files to the final, much smaller image. This makes your application take up less space and is more secure. Full instructions can be found in Official Docker documentation.
Management of multiple services using Docker Compose
It is rare for an application to consist of just one component. Usually you need a database, a cache server (e.g. Redis) or a message broker. Manually running several containers and linking them together would be cumbersome. This is where Docker Compose.
With a single file docker-compose.yml you can define the entire architecture of your application. With a single command (docker-compose up) you run all the necessary services, which immediately „see” each other on a dedicated virtual network. This is ideal for local development. If your goal is to automate the deployment of these containers, be sure to read our post: CI/CD with GitHub Actions - a guide.
Data persistence and container debugging
One of the characteristics of containers is that they are ephemeral - once a container is deleted, all the data inside it is lost. In order to preserve data (e.g. database files), we use the Volumes. They allow you to map a folder from your computer to the inside of the container, keeping your data safe even after a restart of the application.
When something goes wrong, Docker offers a number of debugging tools. Command docker logs allows you to view the output of the application console, and docker exec -it will enable you to „step inside” a working container and check the configuration live. This is the foundation of the modern software engineer's work.
When to switch from Docker to Kubernetes?
Docker works great on single servers and in a development environment. However, if your application is starting to handle huge amounts of traffic and needs to scale to hundreds of containers distributed across multiple machines, it's time to look towards orchestration. If you're interested in this topic, check out our introduction: Kubernetes - first steps.
Optimise your development process
Understanding this, what is docker and how to use containers, is one of the best investments you can make in your programming career or the technological development of your company. No more struggling with missing libraries and different system versions - now your application just works, everywhere.
At 4ADStudio, we help companies fully containerise their infrastructure, which speeds up the deployment of new features and increases the stability of systems.
Do you want to stop wasting time with environmental errors and switch to professional containerisation? Consult us - we can help you build a modern development pipeline!
