Prerequisite Concepts

Suppose you have a website consisting of three components:

• Frontend using React
• Backend using Python API
• Database using PostgreSQL

To develop this project, you need to install tools like Node.js, Python, and PostgreSQL on your system. However, the main challenge is:

How can you ensure that the versions you install do not conflict with the versions required by the project or cause errors?

The solution to this problem is containers.

Containers are isolated processes that run in a separate environment from the main operating system. For each part of the project (frontend, backend, database), a separate container can be defined.

A virtual machine includes a complete operating system and consumes more resources. In contrast, a container only includes the essential components needed to run an application, making it lighter, faster, and more efficient.

A Container Image is a read-only template that includes all the files, configurations, and dependencies required to run a container.

Examples:

• A PostgreSQL image includes: database executable files, configuration files, and required libraries.
• A Python application image includes: the Python interpreter, application code, and required dependencies.

To run a container in another environment (e.g., on a server or a teammate’s system), the image must be shared with that environment.

To store and share images, a Docker Registry is used.

Registry: A central service for storing and managing container images.

Repository: A collection of images related to a specific project or service (e.g., different versions of an application).

The difference between a registry and a repository is that a registry is the storage location for container images, while repositories are collections of related images. In other words, a Registry is like a large library, and a Repository is like a shelf in that library that holds different versions of an Image like books.