Docker image vs Docker container- what’s so different?

If you are a Docker user, you must be confused about how to differentiate a Docker image from a container? Don’t worry, read on and you’ll get your answer.

Both elements (images and containers) are the essential components of a Docker program.

Docker image vs. Docker Container

Docker images are required essentially to shape the containers. Docker images are considered as Blueprint of the Container that can exist in the absence of containers whereas, on the other hand, containers must need them to exist.

To pre-configured the server of environments, Docker images are required whereas containers in order to operate, uses a file system and information for the server provided by an image.

Scroll down to dive into more details about this complicated debate that we’ve made easier for you to understand; either expert would benefit from this blog post.

click to read Docker vs Vagrant

Docker image

It’s An immutable file and set of instructions that provides all the basic commands for an application to be run such as:

  • Dependencies
  • Source code
  • Tools
  • Libraries
  • And other files.

Docker Images are usually considered as snapshots because of having read-only property. All containers are based upon images. Like you must have to use an existing Node container image before building a Node app.

One of the greatest features of these snapshots is to represent the application along with its virtual environment at the same time, thereby allowing developers to test and examine their software in a uniform environment.

A Docker image specifies the following instructions:

  • Which type of external image can be used for a container?
  • Commands to run immediately after the container starts.
  • How to build up accurately the system of a file within a container?
  • Provide instructions for importing the complete data from the host system.
  • Which ports should be available on the container?

You cannot run the images because these are the templates and can only be used as a basis for building up a container (a running image). Once the container is created, a writable layer is added to the immutable image on top to modify.

The separately existing container which is created based on the image, cannot be modified.

A read-write copy of the filesystem (Docker image) is significantly made inside the container whenever a containerized environment is being carried out. The container layer which is added as a result of this action makes it possible for the complete copy of the image to be altered.

A single Docker image base can be used to produce a countless number of Docker images.

Every single time the existing state is saved by modifying the initial state of an image, a brand new template is made with an extra layer on top of it.

Docker images may comprise a series of layers. Each of these layers is distinct but at the same time also stems from the one before it.

A virtual environment is commenced with the help of a container layer. This container layer is attached to image layers which act in place of read-only files.

Docker images, being a part of Docker, provide people (or companies) a means of creating or sharing software. As for the confusion, that if the software in a Docker image could be operated by the computer – the Docker container is always capable of running it.

Docker container

A standard unit of software that packages all three components (libraries, code, and dependencies) together, thereby making it much easier for applications to be run fast, making it possible to run multiple containers within the same host, and allowing the applications to be portable to any computing environment.

A Docker container image provides you everything for running an application such as:

  • System tools
  • Code
  • System libraries
  • Runtime
  • and settings.

Several companies have migrated to containers from VMs just because of the following three features:

  • Lighter
  • Easier to maintain
  • Faster to spin up

You can only version the single container by using its Dockerfile thereby making it much easier for the developers to maintain and run the complete ecosystem of containers.

Because of having a layered architecture (intermediate images), a container usually takes up less space as compared to VMs. Every time while running a new command in your Dockerfile, these intermediate images are created.

But it doesn’t mean that there is no more need for VMS. It is quite essential to have a whole OS for every customer.

Nowadays, VMs are used as middle layers, usually if one having a big server rack that is used by several customers.

Hence containers are much needed not only due to their cheap hardware but because only a few people are required to housekeep the containers. I;e: now you don’t need to focus on housekeeping anymore.

We have now a much better understanding of Docker containers and images. Why not discuss some differences between them?

This is how these two components are in a relationship.


Docker — an open-source project, and a cross-platform program that helps in the development of an application inside isolated containers.

It creates isolated reproducible environments for the applications to build and deploy easily. It is now much easier for developers and IT operations to manage and secure their applications within no time and without advanced technology.

Although the software is easy to handle, few terminologies are there that you must need to know about such as containers, images, and Docker files among others. It is a bit of honest advice to know the actual roles of such components that will help you to speed up learning on the due to work with them.

Although we have got multifarious features from Docker, a few of them are listed below.

  • Easy and faster Configuration

The most significant feature that Docker provides is easy and faster configuration. So, it is much easier to deploy your code within less time. As you can use Docker in multiple environments, the infrastructure’s requirements are not any longer connected with the application’s environment.

  • Increase productivity

Using Docker eases technical configuration as well as rapid deployment of the application. It not only helps in executing the application in an isolated environment but also helps in reducing the sources.

  • Application Isolation

Docker provides containers (each independent to another) that are extremely helpful for applications in an isolated environment. Moreover, it allows us to execute all types of applications.

  • Swarm

Swarm — a clustering and scheduling tool that is used for Docker containers. It uses API as its front end that helps us in managing a cluster of Docker nodes. Moreover, this self-organizing group of engines is used in enabling pluggable backends. Basically, a Docker swarm is an environment where multiple Docker images can run on the same host operating system.

  • Routing Mesh

The routing mesh feature of Docker helps us in enabling all the nodes present in the swarm to accept connections on published ports for any service that is running in the swarm, no matter either the task running on the node or not. It routes incoming requests to all the ports that are published on available nodes to an active container.

Services — the list of multifarious tasks that specify the container’s state inside a cluster. Each task usually represents one instance of a container that you wish to run and Swarm programs them over the nodes.

  • Security Management

Security management not only allows to save secrets into the swarm but also chooses to provide service access to some of the secrets. It includes some basic commands to the engine such as secret inspect, secrete create, etc.

Why Docker?

Docker is supposed to profit every developer and operation engineer. Following are some reasons for using Docker you must need to know about.

  1. It allows us to put in and run computer code packages without worrying about setup or dependencies.

2. For higher figure density, operators usually use Docker to run and manage their apps in an isolated container.

3. Now it’s much easier to set up everything on your own device from scratch as a Docker container can easily be transferred to another device/computer.

4. You can share the Docker container with everyone who actually knows its usage.

Pros and Cons of Using Docker:

Docker Pros:

  • Runs the instrumentation in seconds instead of minutes.
  • Uses less memory.
  • Provides light-weight virtualization.
  • Doesn’t behave like a complete operating system for running applications.
  • Permits you to use a distant repository so that you can easily share your instrumentation with others.
  • Helps in delivering the endless preparation and testing surroundings.

 Docker Cons:

  • In Docker, it’s robust to manage several containers.
  • Several features such as copying files to the container from the host, container self –registration, and much more are missing when using Docker.
  • Another major downside of using Docker is cross-platform compatibility. If there is an application that is specifically designed to run in a Docker container on Linux so that it cannot be able to run on Windows or vice versa.
  • Docker is not a good choice for those applications that need rich graphical interfaces because it is only designed for hosting applications that can run on the command line.

Let’s wrap up

That’s it! This is how Docker can benefit developers. This article brings us to a better understanding of what is Docker. We learned how Docker containers and images are useful along with their relationship, features of Docker, and its pros and cons. It will be much easier for you to recognize the difference between containers and images once you understand the overall process of how to create a container. Although having few downsides, Docker is extremely the best platform for developers and organizations, and do doubt for a good reason.