Menu
Are there any differences in images of Docker and Virtual Machine? Except the image formats, I couldn't find any info on this anywhere. Please comment out on the things like image size, instance creation time, capture time, etc. Thanks!
562
Docker containers are considered suitable to run multiple applications over a single OS kernel; whereas, virtual machines are needed if the applications or services required to run on different OS.
Virtual machines have a host operating system and a guest operating system inside each VM. The guest OS can be any OS, such as Linux or Windows, irrespective of the host OS. In contrast, Docker containers are hosted on a single physical server with the host OS shared among them.
The key difference between a Docker image vs a container is that a Docker image is a template that defines how a container will be realized. A Docker container is a runtime instance of a Docker image. The purpose of this piece is to answer the question, what is a Docker image vs.
The key differentiator between containers and virtual machines is that virtual machines virtualize an entire machine down to the hardware layers and containers only virtualize software layers above the operating system level.
These are some differences between a docker and a VM image which I could list out:
1. Snapshot process is faster in Docker than VMs
We generally start with a base image, and then make our changes, and commit those changes using docker, and it creates an image. This image contains only the differences from the base. When we want to run our image, we also need the base, and it layers our image on top of the base using a layered file system. File system merges the different layers together and we get what we want, and we just need to run it. Since docker typically builds on top of ready-made images from a registry, we rarely have to "snapshot" the whole OS ourself. This ability of Dockers to snapshot the OS into a common image also makes it easy to deploy on other docker hosts.
2. Startup time is less for Docker than VMs
A virtual machine usually takes minutes to start, but containers takes seconds, and sometime even less than a second.
4. Docker images have more portability
Docker images are composed of layers. When we pull or transfer an image, only the layers we haven’t yet in cache are retrieved. That means that if we use multiple images based on the same base Operating System, the base layer is created or retrieved only once. VM images doesn't have this flexibility.
5. Docker provides versioning of images
We can use the docker commit command. We can specify two flags: -m and -a. The -m flag allows us to specify a commit message, much like we would with a commit on a version control system:
$ sudo docker commit -m "Added json gem" -a "Kate Smith"
0b2616b0e5a8 ouruser/sinatra:v2
4f177bd27a9ff0f6dc2a830403925b5360bfe0b93d476f7fc3231110e7f71b1c
6. Docker images do not have states
In Docker terminology, a read-only Layer is called an image. An image never changes. Since Docker uses a Union File System, the processes think the whole file system is mounted read-write. But all the changes go to the top-most writeable layer, and underneath, the original file in the read-only image is unchanged. Since images don't change, images do not have state.
7. VMs are hardware-centric and docker containers are application-centric
Let's say we have a container image that is 1GB in size. If we wanted to use a Full VM, we would need to have 1GB times x number of VMs you want. In docker container we can share the bulk of the 1GB and if you have 1000 containers we still might only have a little over 1GB of space for the containers OS, assuming they are all running the same OS image.
8. Supported image formats
Docker images:
VM images:
100
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With