What is the difference between Containers and VMs

Containers vs VMs

Containers vs VMs Overview

Linux® containers and virtual machines (VMs) are packaged computing environments that combine various IT components and isolate them from the rest of the system. Their main differences are in terms of scale and portability.

  • Containers are typically measured by the megabyte. They don’t package anything bigger than an app and all the files necessary to run, and are often used to package single functions that perform specific tasks (known as a microservice). The lightweight nature of containers—and their shared operating system (OS)—makes them very easy to move across multiple environments.
  • VMs are typically measured by the gigabyte. They usually contain their own OS, allowing them to perform multiple resource-intensive functions at once. The increased resources available to VMs allow them to abstract, split, duplicate, and emulate entire servers, OSs, desktops, databases, and networks. 

Beyond the technological differences, comparing containers to VMs is a proxy comparison between emerging IT practices and traditional IT architectures. 

Which one should I use?

That depends—do you need a small instance of something that can be moved easily (containers), or do you need a semi-permanent allocation of custom IT resources?

The small, lightweight nature of containers allows them to be moved easily across bare metal systems as well as public, private, hybrid, and multicloud environments. They’re also the ideal environment to deploy today’s cloud-native apps, which are collections of microservices designed to provide a consistent development and automated  management experience across public, private, hybrid, and multicloud environments. Cloud-native apps help speed up how new apps are built, how existing ones are optimized, how they’re all connected. The caveat is that containers have to be compatible with the underlying OS. Compared to VMs, containers are best used to: 

  • Build cloud-native apps
  • Package microservices
  • Instill DevOps or CI/CD practices
  • Move scalable IT projects across a diverse IT footprint that shares the same OS

VMs are capable of running far more operations than a single container, which is why they are the traditional way monolithic workloads have been (and are still today) packaged. But that expanded functionality makes VMs far less portable because of their dependence on the OS, application, and libraries. Compared to containers, VMs are best used to:

  • House traditional, legacy, and monolithic workloads
  • Isolate risky development cycles
  • Provision infrastructural resources
  • Run a different OS inside another OS

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How do they work?

virtualization vs containers

Virtualization

Software called a hypervisor separates resources from their physical machines so they can be partitioned and dedicated to VMs. When a user issues a VM instruction that requires additional resources from the physical environment, the hypervisor relays the request to the physical system and caches the changes. VMs look and act like physical servers, which can multiply the drawbacks of application dependencies and large OS footprints—a footprint that’s mostly not needed to run a single app or microservice.

Containers

Containers hold a microservice or app and everything it needs to run. Everything within a container is preserved on something called an image—a code-based file that includes all libraries and dependencies. These files can be thought of as a Linux distribution installation because the image comes with RPM packages, and configuration files. Because containers are so small, there are usually hundreds of them loosely coupled together—which is why container orchestration platforms (like Red Hat OpenShift and Kubernetes) are used to provision and manage them.

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