Virtual Machines vs Containers: Understanding the differences and why Containers are preferred

In today's cloud-native world, virtual machines (VMs) and containers are commonly mentioned. Both systems provide application isolation and deployment, but they are based on different principles and provide various benefits.

Let's look at the architecture of virtual machines and containers, why containers are commonly used, and what this means for developers and organizations.

So lets understand what is virtual machine first?

A virtual machine (VM) is an abstraction of a physical machine that allows various operating systems and applications to operate on a single physical server, also known as a host. A VM's main characteristic is its capacity to imitate an entire operating system environment, which allows for perfect isolation between instances.

Virtual Machine’s Architecture

A typical VM architecture consists of the following layers:

i. Physical Hardware (Host Machine):

This is the underlying physical server that contains the CPU, memory, storage, and networking components. It can be a single server or a group of servers in a data center or cloud infrastructure.

ii. Hypervisor:

A Hypervisor (or Virtual Machine Monitor, VMM) is a crucial component that abstracts and isolates the hardware resources (CPU, memory, disk, network) and creates virtual versions of them. There are two types of hypervisors:

• Type 1 (Bare Metal Hypervisor): Installed directly on the physical hardware. Examples include VMware ESXi, Microsoft Hyper-V, and Xen. These provide efficient resource management and high performance.
• Type 2 (Hosted Hypervisor): Runs on top of a host operating system like Linux or Windows. Examples include VirtualBox and VMware Workstation. These are often used for development or testing environments where direct access to hardware is not critical.

iii. Guest Operating System (Guest OS):

Each VM runs a fully isolated guest operating system, which can be a version of Windows, Linux, or any other OS. The guest OS operates as if it is running on dedicated hardware, unaware that it’s sharing resources with other VMs.

iv. Application Stack:

Inside each VM, you can install and run applications just like on a physical machine. Each VM can have its own independent set of software and services, creating a completely isolated environment for development, testing, or production workloads.

Benefits and Use Cases of VMs

• Full Isolation: Since VMs run their own OS, they are completely isolated from one another. This makes VMs ideal for applications that require high levels of security and resource allocation.
• OS Independence: VMs allow you to run different operating systems on the same hardware. For example, you can run a Linux VM on a Windows host machine.
• Legacy Application Support: VMs are excellent for running older applications that require a specific version of an OS or hardware environment, providing flexibility for migration.
• Complexity and Flexibility: VMs allow for more complex multi-tier applications where each layer (e.g., database, application server, web server) can be isolated in its own VM.

Drawbacks of VMs

• Heavy Resource Consumption: Each VM requires its own OS, leading to significant overhead in terms of CPU, memory, and storage. This results in lower density (fewer VMs per physical server) compared to containers.
• Long Boot Times: Since VMs need to boot up an entire OS, their startup times can be slow, ranging from several seconds to minutes.
• Maintenance Overhead: Each VM requires regular updates and patching of the OS, adding administrative overhead.

Now lets see what are containers.

Containers are designed to be lightweight, efficient, and easily portable. They combine an application and its dependencies (libraries, binaries, and configuration files) into a single isolated entity, but unlike virtual machines, they use the host system's operating system kernel. This makes them faster and more efficient than virtual machines (VMs).

Container’s Architecture

i. Physical Hardware (Host Machine):

The underlying hardware is similar to the VM architecture but is shared across containers rather than virtualized for each instance.

ii. Host Operating System:

Containers share the host OS’s kernel, which eliminates the need for a separate OS for each instance. The host OS must support containerization, such as Linux or Windows with Docker support.

iii. Container Engine (Docker or Docker Engine):

• A container engine like Docker or Kubernetes manages the containers. The engine creates, runs, and stops containers, as well as abstracts and isolates the resources (CPU, memory, storage, etc.) required by each container.
• Docker, one of the most popular container platforms, provides a complete runtime environment for containers and handles everything from container creation to execution.

iv. Containers:

Each container consists of the application and all its dependencies, bundled into a lightweight, self-sufficient package. Containers run as isolated processes in user space on the host OS but share the kernel, making them far more efficient than VMs.

Benefits and Use Cases of Containers

• Lightweight and Resource-Efficient: Containers do not require a full OS, which significantly reduces resource consumption compared to VMs. This allows for higher density (more containers on the same hardware) and better hardware utilization.
• Faster Startup Times: Containers start almost instantly because they don’t need to boot a full operating system. This makes them ideal for microservices architecture, where many small services need to be started and stopped quickly.
• Portability: A containerized application can run the same way regardless of the environment, whether on a developer’s laptop, in a testing environment, or in a production cloud infrastructure. This makes containers highly portable and easy to deploy across different platforms.
• Simplified DevOps and CI/CD Pipelines: Containers have become a cornerstone of DevOps because they enable continuous integration and delivery (CI/CD) pipelines. Developers can create and test applications in containers and ensure that they run consistently in production environments.
• Scalability: Containers are easy to scale horizontally by adding or removing container instances based on demand. This is crucial for cloud-native applications, where resources need to be dynamically allocated to meet varying loads.

Drawbacks of Containers

• Limited OS Compatibility: Since containers share the host OS kernel, they are generally limited to running applications built for the same OS. For example, you cannot run a Windows-based application in a Linux container without additional layers.
• Security: While containers provide some isolation, they share the same host OS, which means that vulnerabilities in the kernel or misconfigurations could potentially lead to security issues across all containers on a host.

So now the question comes, why Containers are preferred over VMs?

As enterprises shift to cloud-native architectures and microservices, containers provide various advantages over virtual machines, including:

• Efficiency: Containers are more resource-efficient since they share the host OS kernel, reducing the need for separate OS instances. This leads to better utilization of hardware resources and lower costs.
• Speed: The ability to start containers almost instantly gives them an edge in environments where rapid deployment is key. This makes them ideal for agile development, where multiple iterations and tests can be run in a short period.
• Portability Across Platforms: Containers are highly portable across different environments, from local development machines to production clouds, making it easier to ensure consistency in application deployment.
• Microservices Architecture: Containers are well-suited for microservices, where an application is broken into small, independent services that can be developed, tested, and scaled individually. VMs are not as efficient in these scenarios due to their heavier resource requirements.
• Simplified DevOps Workflows: Containers streamline DevOps practices by enabling better version control, automated testing, and deployment processes. They integrate seamlessly with CI/CD pipelines, which accelerates the software delivery lifecycle.

While both Virtual Machines and Containers provide environments for application isolation and deployment, containers have become the preferred choice for modern development due to their lightweight nature, efficiency, speed, and scalability. Virtual machines are still valuable for running legacy systems, isolated environments, and applications requiring full OS control. However, for cloud-native applications and microservices architectures, containers offer significant advantages, particularly in terms of resource usage, agility, and portability.