Docker Containers and Virtual Machines Explained

In today’s technology world, two important concepts are Docker Containers and Virtual Machines (VMs). Both play a key role in software development, deployment, and managing infrastructure.

Let’s dive into what Docker Containers and Virtual Machines are, and how they are different, using a technical but easy-to-understand approach.

Docker Containers: Efficient, Isolated Applications

Think of your computer as a big apartment building. Docker Containers are like individual apartments — separate spaces that provide everything one resident (application) needs. They share the building’s plumbing and electrical systems (the Host OS and hardware), making them lightweight and efficient.

Application Containers — Each container is an isolated environment where an application (like App 1, App 2, App 3) runs. Containers share the Host OS kernel but have their filesystems, libraries, and dependencies.

Docker Engine — This is the main tool that helps you create, ship, and run containers. You can think of it like the property management system that keeps everything in the apartment building running smoothly.

Host OS — This is the operating system of the physical or virtual machine where Docker Engine runs. It’s like the foundation of the apartment building.

Infrastructure — This refers to the physical or cloud-based servers that provide computing resources. It’s the land on which your apartment building sits.

Virtual Machines: Full-Fledged Independent Systems

Continuing with our analogy, if Docker Containers are apartments in a complex, Virtual Machines (VMs) are like separate houses, each with its independent systems and utilities.

VM with Apps/Guest OS — Each VM acts like a complete physical computer, with its full operating system (Guest OS) and the application running on top. VMs are completely isolated from each other, and each one needs its share of CPU, memory, and storage.

Hypervisor — This is the software that allows multiple VMs to run on one physical server. You can think of it as the land developer who splits a piece of land into separate lots for individual houses.

Host OS — This is the operating system that runs on the physical hardware, which the Hypervisor then divides to create VMs. In some cases, the hypervisor can run directly on the hardware without needing a Host OS, which is called a Type 1 or bare-metal hypervisor.

Infrastructure — Like with Docker, this is the physical or cloud-based infrastructure that hosts the VMs.

Key Differences Between Docker Containers and Virtual Machines

Isolation — VMs provide hardware-level isolation, meaning each VM is like a separate computer. Containers provide process-level isolation, meaning they share the same OS but run in separate, secure spaces.

Resource Overhead — Containers are more efficient because they share the host system’s kernel, while VMs need to virtualize hardware for each one, which adds more resource use.

Boot Time — Containers start in seconds because they don’t need to boot a full OS. VMs can take minutes since they need to load an entire operating system.

Performance — Containers can have performance close to the host system because they don’t have the extra hypervisor layer. VMs, while offering full isolation, may have slower performance because of hardware emulation.

Management — Containers can be managed using tools like Kubernetes, which can handle a large number of containers easily. Managing VMs requires more resources and is often less flexible.

Docker Containers are ideal for scenarios where you need to run multiple applications on the same operating system efficiently. In contrast, Virtual Machines are better suited when you need to run applications on different operating systems or require full isolation for security or compliance reasons.

As a DevSecOps enthusiast, I hope you enjoy this article. In this column called “Mindful Monday Musings” every Monday, I will share articles on Dev(Sec)Ops and Cloud. You can support M3 (aka Mindful Monday Musings) by following me and sharing your opinions. Please send me your contributions, criticisms, and comments, it would make me glad.