Imagine opening a restaurant franchise where a strict standard must be followed. In Docker, it’s exactly the same.
Dockerfile: The Franchise Manual
When we think of a manual, we remember someone created a step-by-step guide that must be followed strictly. The Dockerfile defines this entire roadmap: it determines how the image should be created, built, and run.
Join The Writer’s Circle event Example guidelines:
- Which base to use (e.g., Ubuntu);
- Which tools to install (e.g., Nginx);
- What should run on startup.
Dockerfile
FROM ubuntu:20.04
RUN apt update && apt install -y nginx
CMD ["nginx", "-g", "daemon off;"]
O Docker lê esse manual, executa o passo a passo e gera uma Imagem. Image: The Standard Template
The image is the ready-made franchise template; it’s the standard that all “units” will follow. Like any franchise standard, the image is immutable. It serves as the base for creating containers, ensuring that all of them start exactly alike.
Containers: The Franchise Units
A container is the restaurant operating in practice. Each container is an instance of the image. You can have multiple containers running simultaneously:
- Unit in Neighborhood A;
- Unit in Neighborhood B;
- Unit in Neighborhood C.
All follow the same standard, but operate independently.
Configurations: Local Adaptations
Although they follow the standard, each franchise can have particularities:
- Different prices;
- Specific promotions;
- Distinct environments.
In Docker, these are the configurations:
- Environment variables;
- Volumes (storage);
- Ports;
- Configuration files.
In other words: we have the same base, but with adapted behaviors.
References
- Docker Docs — What is an image? — explains images, layers, and Dockerfiles.
- Docker Docs — What is a container? — presents the relationship between images and containers.
- LINUXtips — Docker Essentials — course used as the basis for my studies and these notes.