It is always the right call to understand the topics from scratch when we start discussing something new. In our case, we are trying to untangle and elaborate docker image vs. container. You might also call this a comparison of docker vs. container. But one needs to understand first what is docker image and what is docker container.
Let’s not waste our time, and let’s start to explore every detail about the docker vs container.
So let’s commence by defining two significant things:
• What is a docker image?
• What is a docker container?
Table of Contents
What Is A Docker Image?
Before talking about the docker image or docker container vs. image, let’s first discuss what is docker.
Well, do you remember cargo ships? Those big ships that carry big boxes or we can say big containers that have their own distinct objectives and ID.
Those containers contain unique items and are required to make that specific box useful for that particular company or individual who asked for the container to be shipped for them. These items are packed in boxes in such a way that they are useful for someone who has asked them to be shipped. The packaging in boxes is also called dockerized or containerized.
If you find these things difficult to understand or confusing, let me define docker in technical terms then we will start with docker container vs. image.
Docker is a kind of platform-as-a-service i.e., a PaaS product whose main purpose is to isolate virtual environments to deploy, build, and test applications that are usually not meant to work with the current operating system or we can say applications that are incompatible with the current operating system. It is an open-source, virtualization software designed to make developers work easy.
Let’s step back to docker images, before jumping to docker image vs. container.
Docker Images
A docker image is like a snapshot in other types of VM environments in other words it is a kind of readymade software designed with source codes, libraries, tools, and other miscellaneous files that are needed for any application to get developed and run successfully on any operating system and platform.
Docker Images= a collection of files+ some metadata
Dockerfile- build- image- run- containers
Docker Container
It is nothing but an environment virtualized during run-time to allow users to isolate applications from the system underpinning it. They are entirely autonomous and render essential service components by providing strong isolation.
How are Docker Containers Useful?
When docker images run on docker engines they become docker containers. Comparing image vs. container, containers are popular amongst developers and companies of all sizes because it is:
Standardized: Docker has developed the industry standard for containers because of which they are easily portable anywhere.
Lightweight: Containers share the machine’s operating system and do not require an operating system as per the application and it reduces server and licensing costs.
Secure: Docker provides strong default isolation capabilities in the industry and applications are always safer in containers.
Talking about container image files, they are complete, static, and executable versions of an application. Now that we have covered all the basics of docker images and containers, we can jump to the docker container vs. image i.e., how the docker container is different from the image.
But do you know the structure of the docker image? There are layers of software that make up a Docker image. These layers make it easier to configure the dependencies needed to execute the container.
AI development services can be used to analyze and optimize Docker images, helping to identify potential vulnerabilities and improve performance.
So let’s check out the structure of the docker image.
Base Image: The basic image is made from scratch, it will be the starting point for the majority of Dockerfiles.
Parent Image: By using the FROM command, we can refer to the parent image in the Dockerfile. Parent image is the image that our image is based on.
Layers: Numerous layers are added to the base image that creates a sequence of intermediary images. Docker has storage drives that handle the management of image layer contents.
Container layer: A Docker image creates a new container and also a writable container layer. The layer hosts changes that are made to the running container and stores newly written and deleted files as well as changes to the files that already exist. The layer can be also used to customize containers.
Docker manifest: It is an additional file in the Docker image and it uses JSON i,e., javascript object notation format to define the image by using information such as image tags and digital signatures.
From Dockerfile to Image to Container
The process from a docker file to an image to a container starts with the script of instructions that explain how to build a specific docker image and clears your doubt regarding the docker image vs. container. The script of instructions is known as Dockerfile.
The command for creating an image from a Dockerfile is docker build.
The developer can copy and run an application from the template. The application always needs an isolated environment to run that is a container.
The image created completely relies on the source code, files, dependencies, and binary libraries which are all found in the Docker image and which are further used to make up a container.
Use the command docker create to create a container layer from an image.
At the final stage, after the launch of a container from the image already uploaded, you can begin the service and run the application.
The crucial thing to understand about use of Docker is that it has two main components:
• The client CLI tool
• The container runtime
The CLI tool is used to execute instructions to the Docker runtime at the command line. The role of the Docker runtime is to create containers and run them on the OS.
How To Create A Docker Image?
Well! Talking about docker image vs. container there are two methods to create a docker image:
» Interactive
» Dockerfile method
Let’s discuss both methods in brief.
Interactive method: In this method, users can run a container from an existing Docker image and manually make the necessary changes as per the requirements of the environment before saving the image. It is the easiest way to create a docker image.
Dockerfile method: This method requires making a plain text Dockerfile that makes the specifications for creating an image. The whole method is difficult and time-consuming but the benefit is it does well in continuous delivery environments. The whole process includes creating the Dockerfile and adding every command needed for the image.
Once the Dockerfile starts, the user can set up a .dockerignore file to exclude any files that are not needed for the final build. The file is in the root directory. The Docker images command is always used to see the created image.
Docker Image vs. Container
You might have a question is docker a container or are docker and container are same? Well, if we see container vs. docker that is if we compare container and docker, the answer is not exactly.
If we talk about the lower level, a container is just a set of steps that are isolated from the rest of the system. A Docker container is just a runnable instance of an image. At the same time, it will not be wise to say that docker is different from containers.
The following are a few main differences between a Docker Image vs Container:
Docker Image
» It is a source code for the docker container.
» The docker image is a blueprint of the container.
» The image is a logical entity.
» The docker image can be created only once.
» With the help of the docker registry, docker images can be shared between users.
» One cannot attach volumes and networks and hence the images are rigid.
» You must have to write a script in a Dockerfile to make a Docker image.
» It is possible to share a docker image.
» It contains multiple read-only layers.
» Images can be shared on Docker Hub.
» These image templates can exist in isolation.
» There is nothing like running the state of a Docker image.
» Computing resources to work is not required for images.
Docker Container
» It is the instance of the docker image.
» The docker container is a specimen of the image.
» It is a real-world entity.
» Containers are created numerous times using an image.
» It cannot be shared between the users.
» One can attach volumes, networks, etc. but it is only possible if the containers change ie., the old image is deleted and a new one is used to build the container.
» You have to run a command that is “docker run <image>” to make a container from an image.
» It is not possible to share containers.
» Discussing docker container vs Image, the container contains a single writable layer.
» Always docker images are shared because there is no sense in sharing a running entity.
» These containers cannot exist without images.
» Docker containers use RAM when created and in a running state.
» Containers need computing resources to run as they run with a Docker Virtual Machine.
Benefits Of Docker
There are several benefits of docker in building and deploying applications. Here are some of them listed below:
• Flexible resource sharing
• Scalability, you can place many containers in a single host
• Fast deployment
• Faster migration
• Ease of moving and maintaining your applications
• Better security
• Less access is needed to work with the code running inside containers
• Fewer software dependencies
Always keep these benefits in mind whenever you create the container infrastructure while building applications in the cloud.
Conclusion
Once you understand the whole process of creating a container you will get to know what docker container vs. image actually means. After reading this blog you must have got a better understanding of what a Docker image is what a container is and how they are connected to each other.
A container needs an image to run and it always depends on the image to create a run-time environment for running and deploying applications.
Now that you have a fair knowledge of both concepts of docker container vs. image, you have to keep in mind that an image can exist without a container, but vice versa is not possible.
Frequently Asked Questions
Q1. What Is the Difference between Container and Container Image in Docker?
Ans. The major difference between a Docker image and a container is that a Docker image is a read-only permanent template that elaborates how a container is going to be realized.
Q2. What Are Docker Image And Docker Container?
Ans. A Docker image is a file used to implement code in a Docker container. Docker images function as arranged instructions to develop a Docker container like a template. Docker images function just like this at the starting point when using Docker. An image is proportionate to a snapshot in a virtual machine, i.e., a VM environment.
Q3. How To Convert Docker Container To Image?
Ans. You can convert a Docker container to an image in the eight best steps. These steps are mentioned below:
• Create a base container
• Examine images
• Examine containers
• Start the container
• Alter the running container
• Generate an image from a container
• Tag the image
• Generate images with tags.
Q4. Where Is Docker Image Stored?
Ans. By default, Docker uses the Overlay2 driver, with the help of which it stores the images in a directory which is known as /var/lib/docker/overlay2.
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