Docker Image vs Container: The Key Differences

It is always wise to first understand the concept of subjects that are under consideration in our discussion here. In our case, we are trying to decode the difference between the Docker image and container, which we know are the core Objects of the Docker as an ecosystem. Many people also call this comparison as docker image vs container which I feel is not right to do because one needs to first understand the core objects which make docker system and try to decode those objects if they want to compare them  

So let’s first define 

• What Is Docker Image? 
• What Is Docker Container?  

What is Docker Image

Let’s start by understanding - 

What Is Docker? 

Well, I always like to call Docker a mammoth cargo ship that has the ability to hold big boxes (containers) having their distinct objectives and id. These boxes contain items that are unique and are required to make that particular box useful for the company/person who has asked for it to be shipped. These items are first manufactured in factories that have templates to reproduce such items. These items (images) are packaged into the boxes (dockerized/containerized) in such a manner that they are useful for someone who has asked them to be shipped.  

If you are finding this analogy hard to digest, let me define it by keeping its technical aesthetics in place 

Docker is open-source, virtualization software created to make developer's life easy. It is a kind of PaaS (platform-as-a-service) product whose core objective is to isolate virtual environments to deploy, build, and test applications that are usually incompatible or not meant to work with the current OS. 

So let’s come back to docker images.  

Docker Images

It is a kind of ready-to-use software read-only template crafted with source codes, libraries, external dependencies, tools, and other miscellaneous files that are needed for any software application to run successfully on any platform or OS.  

The developer community also likes to call it Snapshots, representing the app and its virtual environment at a specific point in time.  

This docker snapshot is a perfect recipe for developers to build test and deploy the desired app swiftly. Know more about introduction to docker, docker containers & docker hub. 

What is Docker Container?

Now that you have got hold of the docker image concept it will be apt now to describe the docker container.  

As we discussed, docker images are nothing but a read-only template that can’t be executed by themselves and cannot run or start. If that is the limitation how can one make a real value out of it?  

Well, the answer lies in the concept of the Docker container.

Docker Container 

A container is nothing but a box that has the ability to run the docker image templates. The moment you create a container using those immutable images you essentially end up creating a read-write copy of that filesystem (docker image) inside the given container. This adds a container layer which helps you to modify the entire copy of the given Docker image. 

A container can also be considered as a cohesive software unit that packages up code and all its dependencies so the application runs quickly and reliably from one computing environment to another.  

If your curiosity is not settling down why don’t you go ahead and check out this course learning docker online?

Docker Image vs Container Comparison Table

Now that we have an idea about docker image vs container, let us understand the difference between docker image and container based on the parameters below. 

Parameter	Docker Image	Container
State	Static template hence Immutable	Dynamic hence Mutable
Scalability	Less scalable	Highly Scalable.
Size	Lightweight.	Heavier than docker image.
Creation	Created from a Docker file	Created from a Docker image
Portability	Highly portable	Less portable than Docker image
Resource Sharing	Shared resources.	Resources are shared maintaining isolation.
Isolation	Image-level isolation	Process-level isolation
Lifecycle	Persistent across various platforms.	Short-lived
Startup time	More unless images are cached	Relatively lesser

I hope this table gave you a gist of the difference between container and docker.

Docker Image vs Container

stack-overflow 

Let me elaborate on each of the parameters mentioned above. This detailed exploration will enhance your understanding of the difference between docker image and docker container. 

Docker Image vs Container : State

Docker Image: An image's contents cannot be modified once it's created, promises reproducibility and uniformity amongst containers. Making changes calls for an entirely new image.

Container: Throughout their lifecycle, containers can be modified and be in any of the following states: running, paused, or stopped. IT enables adjustment and personalization over the course of the container's life.

Docker Image vs Container : Scalability

Docker Image: Images created with Docker are not naturally scalable. The only scalability they provide is to allow for multiple container creation from one image.

Container: Dynamic scaling revolves around containers because of their high scalability. They enable the distribution and replication of an application among several instances in response to different workloads.

Docker Image vs Container : Size

Docker Image: Lightweight because it is static and does not include active resources or running processes.

Container: Bigger than the image because it has resources allotted to it and multiple running processes. 

Docker Image vs Container : Creation

Docker Image: Built using a Dockerfile that provides layer-by-layer construction instructions for the image.

Container: It is created from a Docker image using the “docker run” command, with various optional configurations set at runtime.

Docker Image vs Container : Portability

Docker Image: It is simple to share, version, and deploy uniformly in various environments.

Container: Although it is less portable, it ensures consistent behavior across different platforms by encapsulating the application and its dependencies.

Docker Image vs Container : Resource Sharing

Docker Image: By sharing layers, images minimize redundancy and maximize disc space. Nevertheless, dynamic resource scaling does not directly involve images.

Container: Because they can scale both vertically i.e. increasing resources for a single container and horizontally i.e. replicating containers to distribute the load, containers are an efficient use of resources.

Docker Image vs Container : Isolation

Docker Image: Ensures that the contents of the image are self-contained by providing isolation at the image level.

Container: Permits independent application operation without interfering with one another. Although they have distinct user spaces, containers share the host OS kernel.

Docker Image vs Container : Lifecycle

Docker Image: Enduring in various environments, supporting rollbacks, versioning, and upholding a standard build procedure.

Container: Makes replacement, starting, and stopping simple. This makes orchestration, dynamic scaling, and resource efficiency possible.

Docker Image vs Container : Startup Time

Docker Image: Setting up the Docker process from scratch can take time unless the image is cached. Depending on the size of the image, internet speed, and availability of local cache, this may take a few seconds.

Container: A container is an already-configured instance of a Docker image, with its environment ready to go. When compared to pulling and preparing an image from scratch, this results in faster startup times.

Difference between Docker image and containers?

To be true if you see the docker ecosystem in its entirety you will agree that both of these docker objects are an inclusive part of it. Without docker images, you can imagine docker containers at all and without docker containers, docker images are like completely meaningless and orphans.  

So is it wise to compare them, I may say no but still to clarify the concepts we can do so only on the basis of their roles and responsibilities  

Docker Image vs Container

• The key difference between a docker image vs container is that a Docker image is a read-only immutable template that defines how a container will be realized. A Docker container is a runtime instance of a Docker image that gets created when the $ docker run command is implemented.  
• Before the docker container can even exist docker templates/images are built using $ docker build CLI. 
• Docker image templates can exist in isolation but containers can't exist without images.  
• So docker image is an integral part of containers that differs only because of their objectives which we have already covered.  
• Docker images can’t be paused or started but a Docker container is a run time instance that can be started or paused.

When to use: Docker image vs container

In the battle between linux containers vs docker you must be confused which one to pick, let me help you with it.

When you wish to package and distribute applications uniformly across various environments, use Docker images. Docker images encapsulate an application's code, dependencies, and runtime, acting as immutable blueprints. Versioning these images makes them more reproducible and gives deployment a solid base.

However, when you're prepared to run and execute applications, use Docker containers. Applications have access to a lightweight, isolated runtime environment through containers, which are instantiated from Docker images. Containers make it possible to scale easily, manage more effectively, and use resources more efficiently. They are perfect for workloads that change frequently because they make it easy to replicate and orchestrate apps. To sum up, Docker images serve as the foundation for applications and guarantee consistency, whereas Docker containers are the dynamic, runnable instances that give those applications life and allow for greater deployment workflow agility and scalability.

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Benefits of Using Containers and Docker

I am sure you must have been clear with the concepts of docker vs container. Now let us look at some of the pros of using the duo to get a better understanding of the difference between docker and container.

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1. Fast Deployment: Applications can be deployed consistently and quickly thanks to containers. Because containers are lightweight and quick to instantiate, applications can be scaled up or down dynamically in response to shifting workloads. This flexibility is particularly important in contemporary dynamic environments where applications must quickly adapt.
2. Increased security: It is far safer to store sensitive data and files in containers because they stay in a separate location. It keeps sensitive files safe from other servers and offers increased security for them.
3. Integration of DevOps with CI/CD: Because they enable smooth integration with CI/CD pipelines, containers are essential to DevOps processes. Specifically, Docker has established itself as a go-to tool for automating software delivery. Containers streamline the deployment pipeline and lower deployment friction by ensuring that applications behave consistently in development, testing, and production environments.
4. Lower expenses: Using a Docker container helps users cut back on the high cost of infrastructure. Users can run multiple applications at very low speeds with Docker platforms. It consequently raises the return on investment automatically.
5. Efficient multi-cloud environment management: With the rise in popularity of cloud computing in recent years, every organization is setting up a multi-cloud infrastructure. It offers the capability for effective information storage in containers integrated with cloud environments and guards against any information being destroyed in Docker containers.

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Use Cases for Containers and Docker 

There can be multiple use cases for docker image vs container, have a look at some of the primary cases.

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1. Microservices Architecture: Docker is an excellent tool for developing and implementing microservices applications because it provides isolation, scalability, and quick deployment for every service component.
2. Cloud-Native Applications: The foundation of cloud-native development is containers, which enable resource optimization, scalability, and portability in cloud environments.
3. Server Hosting: Multiple servers can be hosted by Docker containers due to their robustness. When necessary, Docker can generate reverse proxy servers in addition to working with file and web servers.
4. DevOps Interaction: By enabling shared container images and environments and streamlining the processes for testing, debugging, and deployment, Docker facilitates collaboration between development and operations teams.
5. Modernizing Legacy Applications: Docker can containerize current applications, giving them the benefit of improved resource efficiency, scalability, and isolation while running in contemporary environments.

Which to Choose: Containers or Docker?

Picking "engine" or "car" is akin to selecting "containers" or "Docker". The technology, the engine driving portability, scalability, and isolation, is containers. The tool, or platform, that makes it simple to create, administer, and implement containerized applications is called Docker.

Your individual requirements will determine which option is best for you. Docker images are crucial to the packaging and distribution of an application in a consistent and portable manner. Dealing with containers is essential if your goal is to run and manage applications in a secluded and effective environment. Both are typically used in tandem to enable a comprehensive approach to modern application deployment and management: containers are used to execute applications, while Docker images are used to encapsulate them.

Wrapping Up

Docker and Container is a Strong Pair. Because of their close relationship, to understand Docker image vs container can be confusing. They are two sides of the same coin, not interchangeable. Pictures are the models, the still recipes; and containers are the completed cakes, the instances that are brought to life from those models.

Docker images lay the groundwork for standardized application packaging, but containers make these blueprints a reality by promoting scalability, agility, and effective management. Combining the two simplifies the development-to-deployment process and provides a complete solution for building, distributing, and executing applications in a variety of settings. In the age of containerization, Docker images and containers work together to completely rethink how we design, build, and run applications.