Main concepts
Images are blueprint for containers and are read only.
An image include:
- a runtime environment (e.g., Node, the runtime environment for JavaScript)
- the whole application code
- any dependencies
- extra configuration (e.g., ENV (environment variables))
- commands (e.g.,
npm install)
Containers are running instance of an image: a container runs our application
- containers are isolated process
Given the fact that an image is a blueprint of an application, is completely shareable (even though the source code is present and it may include heavy files).
An image can produce more containers
How an image is composed
Images are made up from several “layers”
- the base layer is a parent image, that includes a lightweight OS and the runtime environment. Common parent images are found in Docker Hub
- the source code, with commands needed to execute it
- dependencies