Virtual machines and containers are types of virtualization that allow applications to be deployed inside environments isolated from the underlying hardware.
These technologies are often used in large IT projects to cut costs and make deploying programs on different platforms easier. A virtual machine is also useful for trying out new operating systems.
One problem with these concepts is that they are highly similar, making choosing between them difficult.
So what exactly is the difference between a virtual machine and a container?
What Is a Virtual Machine?
A virtual machine is a virtualization of a computer. Virtual machines allow you to use a single computer to run what appear to be multiple computers, each with its own operating system.
Virtual machines are created using hypervisors. This is a piece of software that sits between a VM and the underlying hardware. The hypervisor takes resources from the underlying hardware and partitions them to dedicated to individual VMs.
The result is multiple environments that use the same hardware but behave as if they are completely isolated from each other.
What Is a Container?
A container is similar to a virtual machine. But instead of virtualizing an entire computer, a container only virtualizes software above the operating system level.
Containers are lighter because they don't need their own operating systems. To put this in perspective, they are usually measured in megabytes rather than the gigabytes associated with virtual machines.
They also don't need a hypervisor and can be placed directly on top of the host operating system. Each container then shares the host OS kernel.
While smaller than virtual machines, containers are still designed to include all necessary files for an application to run. They include all dependencies and run-time libraries. This allows an application inside a container to be run anywhere.
What Is the Difference Between a Virtual Machine and Container?
Virtual machines have been around the longest, but they have been replaced by containers for some purposes. Each technology, however, has its own pros and cons. The right tool for the job, therefore, depends on the specific project. Here are the primary differences.
1. Virtual Machines Provide a Separate OS
Due to having their own operating system, virtual machines can perform a number of tasks not possible with containers.
- You can run programs that are not compatible with the host OS.
- You can run multiple applications in different operating systems.
- You can run multiple applications that cannot afford to share operating system functionality and resources.
2. Containers Are Smaller and More Portable
Sharing an operating system greatly reduces the amount of code necessary for a container to run. Containers are therefore significantly smaller than VMs, often taking up only a few megabytes.
This makes containers potentially much cheaper because you can fit more of them on a single server. It also makes containers significantly more portable.
Containers can easily be transferred between computers, computing environments, and the cloud. This makes them particularly useful for teams who want to collaborate on a single application while using different environments.
3. Containers Start Up Faster
Containers can be launched much faster because the operating system is already running, unlike launching a virtual machine, which involves booting up a new OS.
Containers can therefore start up in seconds, while virtual machines usually require a few minutes.
Because containers use fewer resources, they also allow some applications to run faster.
4. Containers Have Access to All Resources
Virtual machines have specific resources allocated to them by the hypervisor. This can be useful for resource-intensive applications, but it can also be inefficient when allocated resources are left unused.
Containers have access to all of the underlying hardware resources and therefore do not pose this problem. As a result, containers are usually the better choice for applications where the resources needed are unknown.
5. Virtual Machines Are More Secure
A virtual machine is completely isolated from everything else on a computer. A container is only isolated at the process level. This makes virtual machines more secure.
If the host operating system is compromised, all of the containers installed above it may also be compromised. In the same scenario, virtual machines would be unaffected.
An exploit running inside of a virtual machine cannot affect anything outside of it. An exploit running inside of a container can potentially access the rest of a system.
Should You Use a Virtual Machine or a Container?
Virtual machines and containers are very similar to each other, but they are not interchangeable. Consequently, some projects will offer a choice between the two while others will not.
You should use a virtual machine when you want to run applications that specifically require a new OS. For example, the host OS may not support the application.
A virtual machine should also be used when isolation and security are prioritized above all else.
In most other scenarios, a container will provide a lighter, faster, more cost-effective solution.
Can You Use Virtual Machines and Containers Together?
If you want the functionality of both virtual machines and containers, it is possible to combine the two. In this case, you launch a virtual machine and then deploy containers inside of it.
This is particularly useful for security purposes. For example, imagine you run ten containers on a single computer. If that computer's OS is compromised, all ten containers might be affected.
Now imagine you divide those ten containers across multiple virtual machines. If one of those VMs is compromised, only the containers inside it will be affected, and the rest will operate as normal.
Are Containers Replacing Virtual Machines?
Containers are increasingly popular and with very good reason. They achieve many of the same goals as virtual machines, yet they do so at a fraction of the size and potential cost.
Despite this fact, there are many situations when only a virtual machine will provide the desired functionality, meaning that VMs, regardless of their size, will always be utilized to some extent.