Containers vs. Virtual Machines

2.1 Virtual Machines

The concept of virtualization dates back to the 1960s when IBM developed virtual machines for its mainframes. This allowed efficient use of computer resources and workload isolation. Since then, virtualization has evolved and has become a key part of IT infrastructure.

A virtual machine (VM) is a software emulation of a physical computer. It allows you to run operating systems and applications as if they were operating on a separate physical server. The main components of a VM are the hypervisor, guest operating system, and applications.

The hypervisor is software designed to manage virtual machines and share resources among them. There are two types of hypervisors:

• Type 1 (bare-metal): Installed directly on the hardware. Offers high performance and minimal overhead. Examples: VMware ESXi, Microsoft Hyper-V.
• Type 2 (hosted): Runs on top of a host operating system, making it more flexible but less performant. Examples: Oracle VirtualBox, VMware Workstation.

Guest OS: Each virtual machine contains a complete operating system running on top of the hypervisor. This allows you to use different operating systems on the same physical server.

Applications: Applications and their dependencies are installed within the guest OS, ensuring isolation and independence.

Advantages:

• Isolation: Virtual machines are completely isolated since each VM has its own operating system and resources. This prevents one application's impact on another.
• Compatibility: Virtual machines can support any operating system, including different versions of the same OS, providing flexibility.
• Security: The high level of isolation makes VMs more secure — vulnerabilities in one VM can't easily affect others.

Disadvantages:

Resource-intensive: Each VM requires significant resources because it contains a full operating system. This increases demands for RAM and disk space.

Startup: Virtual machines take longer to start and stop due to the need to boot up and shut down the operating system.

Management: Administering multiple VMs can be complex and time-consuming, especially in large infrastructures.

2.2 Containers

Containerization as a concept has been around for decades, but it became widely popular with the rise of Docker, which appeared in 2013. Docker made using containers easier and more accessible for most developers and system admins.

Containers differ from virtual machines because they use the host operating system kernel and provide process-level isolation. You can run apps and their dependencies in isolated environments without installing a separate operating system.

• Host OS: containers use the kernel of the host operating system, which helps save resources and reduce overhead.
• Containers: each container includes the application and all its dependencies but doesn’t come with a separate operating system. Container isolation is enabled by technologies like namespaces and cgroups, which limit resource access and split processes.
• Namespaces: a Linux kernel mechanism that creates an isolated environment for processes, hiding from them the processes, file system, network interfaces, and other resources of other containers.
• Cgroups: a resource management technology that lets you control the use of CPU, memory, disk I/O, and other resources by containers, preventing their overuse.

Advantages:

• Lightweight: Containers require fewer resources because they don’t need a separate operating system. You can run more containers on a single physical server compared to virtual machines.
• Fast startup: containers start and stop way faster than virtual machines since there’s no need to boot up or shut down an operating system.
• Portability: containers are easy to move between different environments because they include all the dependencies an app needs. You can create unified images that will work on different platforms without changes.

Disadvantages:

• Isolation: container isolation isn’t as strict as with virtual machines since they share the host operating system kernel. If an app in a container is compromised, it could create potential vulnerabilities.
• Compatibility: containers need to be compatible with the host operating system, which can restrict their use in some scenarios.

2.3 Comparing Containers and Virtual Machines

Resource Usage:

• Containers: need fewer resources and use RAM and CPU more efficiently. You can run more containers on a single physical server, making them cost-effective for scaling.
• Virtual Machines: consume more resources because they require a full-fledged operating system. Each virtual machine takes up a significant amount of RAM and disk space, limiting the number of VMs on one server.

Speed:

• Containers: start and stop in just a few seconds, making them ideal for tasks needing quick response and scaling.
• Virtual Machines: take longer to start and stop because they need to boot the operating system. Booting a VM can take several minutes, which limits their use in dynamic environments.

Isolation:

• Containers: provide process-level isolation. The level of isolation is lower than that of virtual machines but is enough for most apps. Not suitable for tasks needing full isolation and maximum security.
• Virtual Machines: provide full isolation at the operating system level. The high level of isolation makes them the best choice for critical apps and data.

Management and Scalability:

• Containers: easy to manage and scale because they're lightweight and start quickly. Orchestration tools like Kubernetes simplify managing large container clusters.
• Virtual Machines: managing and scaling is more complex due to high resource consumption. Administering many VMs requires significant effort, especially in dynamic environments.

Choosing between containers and virtual machines depends on the specific tasks. Containers are optimal when fast deployment and app scaling are needed with minimal resource costs. Their portability and lightweight nature make them a great fit for microservice architecture and cloud computing.

Virtual machines offer better isolation and compatibility, making them the go-to for complex and critical apps requiring high levels of security and independence. They're indispensable when deploying multilayered apps and infrastructures that need a full operating system for each workload.

In practice, many organizations use a hybrid approach, combining containers and virtual machines to achieve the best balance between performance, flexibility, and security.