What is a base image (base image)?

A base image is the source image from which the build of a Docker image starts. It sets the starting file system and environment on top of which the layers with the application and dependencies are added.

#Example to understand this

In a Dockerfile, the line:

means that the base will be Ubuntu, and after that we will stack our own layers on top: copy files, install packages, and so on.

#What a base image can be

1. An OS as the foundation ubuntu, alpine, debian - a minimal system for applications.
2. A language-based foundation python:3.10, node:18, openjdk:17 - already pre-installed runtimes.
3. An empty foundation (scratch) FROM scratch - a completely empty base layer for ultra-light images.

#Why a base image is needed

• it sets the environment and file system for the future container;
• it removes the need to configure everything from scratch;
• it speeds up the build thanks to ready-made layers.

In short: a base image is the foundation on which the rest of the image's layers are "built up" in the Dockerfile.