What Are Containers? Differences from VMs and Docker Basics

What is a container

A container is a virtualization solution at the operating‑system level, so it can only run operating systems that share the same kernel as the host.

Differences between containers and virtual machines

Virtual machines are based on the host hardware, while containers rely on the host operating system.

Virtual machines can run any operating system, even different from the host; containers can only run systems with the same kernel as the host.

Virtual machines consume many resources because they run a full OS; containers share the host’s resources, allowing many more applications to run under the same resources.

What is Docker

Docker is an open‑source container engine written in Go, built on the Linux kernel, and therefore runs on Linux systems.

Docker’s goals

Docker aims to solve environment‑dependency problems, such as:

Dependency conflicts – e.g., one site needs PHP 4 while another needs PHP 5; Docker isolates them.

Missing dependencies – setting up a new environment often requires installing many packages; Docker packages them together.

Platform dependencies – differing platform versions no longer cause issues because Docker runs consistently across platforms.

Docker use cases

Developing, testing, and deploying services with containers – developers can create, build, and share Docker containers locally, then move them to testing and production.

Creating isolated runtime environments – different service versions or user groups can run in separate containers.

Setting up test environments – complex clusters can be assembled locally with ease.

Building PaaS infrastructure to provide SaaS applications.

High‑performance, large‑scale host deployments – many cloud platforms support Docker, simplifying service deployment.