The present world is full of multiple technologies that run in different environments. Most of the time, people have to work on a variety of software and hardware platforms simultaneously. This led to the creation of virtualization in the IT world, which satisfies the need to run multiple different machines (desktops, servers, handhelds, laptops, etc.) platforms that have their customized hardware and software as per their specific usage. 

In simple terms, virtualization is the process of running multiple simulated environments in one machine without the need to install or configure them. More technically, it refers to an abstract layer that shares the resources of infrastructure among various simulated Virtual Machines so that a physical set-up of an environment is not needed. A detailed analysis of Docker Vs VM is provided in this article for a comparative study.  

What Are Virtual Machines Or VM’s ?

Virtual Machines or VMs refer to simulated virtualized environments. They are not actual physical machines but a replication or in more technical terms, a simulation of such machines. A good replication is that it copies all the features of the original into it and so do the Virtual Machines. They act just like a real physical machine and use physical sources of the underlying host operating system. It can be said that a Virtual Machine is perhaps a running instance of a real physical machine. They have their pros but there are some drawbacks to them as well –

• All systems can’t be virtualized. This reduces the scope of VM utilization to a great extent. 
• Too many VMs increases payload on CPU resources which leads to the latency of virtual disks.
• Performance is not very stable.
• A corrupt VM can sometimes affect other VMs or the kernel (as in the case of Type-1 or bare-metal hypervisor).

To overcome all these flaws of VMs, an alternative approach was introduced, namely containerization. It is OS-level virtualization in which the entire build of an application and run-time environment is packed up in a container. Containers are lightweight virtualized environments that are independent of the infrastructures. 

What Are Dockers?

Dockers are frameworks created for containerization, to build, ship, and run distributed applications over multiple platforms. A Docker framework can be divided into a Docker engine, that is installed on the host OS, and a Docker daemon, that starts the process of managing virtual containers. The instruction file, called the Dockerfile, is built and packaged with its run-time environment as an executable file, called the Docker image. Docker daemons run Docker images to create Docker containers. 

Differences Between Dockers and Virtual Machines Based On Various Parameters

• Architecture and Installation

Virtual Machines have hardware-level virtualization whereas Dockers have software-level virtualization. The hypervisor of VMs can run on hardware resources (have their OS) or on host OS while Dockers run on host OS only. On a host OS, the Docker engine is installed and the Docker daemon process is initiated. Each container has the same host OS.   

• Isolation

VMs have full isolation whereas Dockers have a process or application-level isolation.

• CPU Processing and Performance

VMs are slower than Dockers because a VM has the entire run-time environment which needs to be loaded for every use whereas the pre-built Docker images of a Docker share the resources that it got from the host OS so that running an image as a container is lightweight. Comparatively, Dockers use fewer cycles and provide better and more stable performance than Virtual Machines. 

• Hardware Storage

VMs provide more storage because each VM is an independent machine or OS. For instance, three 800 MB VMs take 2.4 GB of storage space only. On the other hand, Docker containers are very lightweight as they run on the host OS and take its resources.

• Portability

VMs depend on host OS and hardware which makes them comparatively less portable than the highly portable lightweight Dockers which have zero hardware dependency. Importing Virtual Machines require manual setup and such storage, RAM, and network. 

• Scalability and Code Reusability

Spinning up new VMs calls for administrative tasks like the distribution of resources to the Virtual Machine. A new VM increases the load on system resources and re-managing earlier VMs is also required. Since every VM has its copy of resources, the reusability of code is very poor in Virtual Machines. Spinning up new Dockers means running pre-built Docker images into Docker containers. Containers are configured at that time only. Since one Docker image can create many containers so code-reusability is comparatively very high in Dockers.  

• Resource Utilization

VMs have a static allocation of resources whereas Dockers have a dynamic allocation of resources. Static allocation causes resource wastage if there is an increment in the resource requirement of a VM or if the VM is idle. Dynamic and De-allocation of resources in Dockers can be done as per the requirements of the Docker engine. 

• Docker System Prune or Garbage Collection

VMs don’t have an in-built prune mechanism and have to be, therefore, administered manually. Docker images and Docker containers can be pruned to free up storage and memory space and reduce CPU cycles as well.

• New Environment

Creating a new VM is a tedious job that involves repetitive tasks like the installation of a new OS, and loading tools like kernel drivers and configurations. For a new Docker, one needs to pack the code and dependency files, build Docker images, and create new Docker containers. An existing or base image, called scratch (found in Docker Hub), can be run to create more Docker containers on the go. 

The above are just a couple of parameters based on which Dockers and VMs can be distinguished. There are many more parameters that provide a distinction between the two. They have plenty of pros and cons so one needs to know the difference between the two to understand the right usage of the two. VMs and Dockers work on two different principles, namely virtualization and containerization. Dockers were created to overcome the drawbacks of VMs but they have too many advantages to yet go extinct.