Introduction
Docker containerisation is a unique application that helps to quickly deploy and run applications using the containers available on the platform. However, everything on the Docker platform is not the same, meaning a Docker image differs significantly from a Docker container. Both Docker and container serve the same purpose but differ in use cases.
A container holds a lot of information and data in the form of essential files and documents. A Docker image only presents a picture of a particular environment, whereas a Docker container is responsible for running the entire software.
Let’s explore the Docker image vs container concept and closely understand both.
What is a Container?
If you are wondering ‘what is Docker container’, here’s its answer.
A container is a separate area which allows applications to run independently without influencing any other part of the system. Containers are ideal for safely operating applications and databases that contain sensitive information because they are segregated from other parts of the device.
Using containers is very effective since they do not need any overhead or any other part of the operating system. Containers run separately and independently on the operating system. The host machine’s kernel does not get overloaded and has space for executing other applications. Docker users can configure a container as per their requirements.
Containers are also cloud compatible; applications can independently run and integrate with cloud systems. A lot of machinery work is eliminated by building and executing containers inside multiple software. Isolating selective applications from the others in infrastructure is easier with containers.
What is a Docker Image?
Docker images are available only in the read-only format, and these are used to include information about building containers. The Docker platform generates containers applying Docker images. A Docker image is very similar to a picture or a blueprint.
To understand ‘what is a Docker image’, one must know what it contains. A Docker image is composed of multiple layers, just like it exists in a snapshot, and all the layers consist of different parameters having distinctive values according to the environment.
The Docker image consists of various objects, runtimes and binary codes to run an application successfully. All these are done with the help of the host operating system kernel, which acts as the backbone of the Docker image.
Docker users can pull images from other sources and also generate images manually. For generating images manually, the Docker user will write a whole set of codes to create a Docker image or file. If the Docker user wants to pull the images from any other file, then the “Docker pull [name]” command has to be executed.
However, all the Docker images are immutable, and any changes cannot be made after the image is created. To change any characteristic in a Docker image, the user must create an image in another container and save it as a new one.
How do Containers and Docker Work?
One must know how containers and Docker function to fully understand the concept of Docker container vs image. Let’s look at the functionality of Docker images and containers.
Docker image functions on a read-only system, and any changes in an already created image cannot be made. It is immutable and not dynamic. Docker images are only used to write and execute container creation codes. These are a set of guidelines that acts as a template for building containers.
Docker containers function on a read-write basis, allowing the container to alter and modify the files it includes. This helps to connect the container to the intended network. It allows Docker users to make changes in the file system and create network interfaces per the user’s requirements.
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Key Differences Between Containers and Docker
Though belonging to the same platform, Docker images and containers have different use cases and features.
The table below shows the difference between Docker image and container:
| Docker image | Docker container |
| Images are blueprints or templates of a container. | Containers are instances and collections of various images. |
| Images exist on a logical basis and can be created only once. | Containers have real-world applications and can be created several times using images. |
| Images are immutable, and they do not permit any changes or modifications. | Containers allow changes when new images are to be built, and the old ones are lost. |
| Images are simple and can work without any computing resources. | Computing resources are necessary for containers to run the applications in connection with a Docker virtual machine. |
| The creation of an image requires the writing of codes in a Docker file. | When containers are created with the help of Docker images, the user has to execute the Docker run <image>” command. |
| Docker images are utilised to package up applications and make pre-configured servers. | Containers are operated using a file system and server information guided by images. |
| Images can be viewed and shared at the Docker hub. | Containers do not require the concept of sharing, and it is only applicable to images. |
| A Docker image does not come with any running stage. | Containers have different stages of running and use RAM at that time. |
| Any connection with the images is prohibited as it exists only as a picture. | Users cannot connect one container to another to execute and run the commands. |
| Docker images can be shared. | Sharing Docker containers directly is not allowed. |
| Images come in the format of read-only and consist of multiple layers. | Containers come in the read-write format and consist of a single writable layer. |
| The image blueprints can be segregated from containers. | Containers cannot exist without images. |
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Benefits of Using Containers and Docker
Docker has very well captured the containerisation market. It is a popular platform and provides many advantages to the users.
- Consistent environment: Docker is a very consistent platform and provides users with the advantages of consistency in designing and building containers. It is a predictable environment that provides debugging features and eliminates errors for proper configuration.
- Speed and agility: Docker services are fast and do not slow down. It helps users create containers in just a few minutes and deploy them on the intended operating systems without any hindrance.
- Effective management of multi-Cloud environment: Cloud computing has gained popularity in the past few years, and every organisation is installing a multi-cloud facility. It prevents any destruction of information in the Docker containers and provides the facility for efficient storage of information in containers integrated with cloud environments.
- Greater security: As containers remain in an isolated area, it is much safer to store sensitive information and files. It provides enhanced security to the sensitive files and does not let other servers get access to it.
- Reduced costs: Docker container allows users to reduce the enormous infrastructure cost. Docker platforms allow users to run multiple applications at a very minimal rate. Thus, it automatically increases the return on investment.
Drawbacks of Using Containers and Docker
Docker also has some disadvantages. The following are the drawbacks of using containers and Docker:
- Missing features: Docker is not equipped with all the features a user requires, like self-registration, copying files and folders, self-inspection etc.
- No cross-platform compatibility: A significant drawback of Docker containers is that if they are developed on Linux, they cannot operate on Windows and vice versa.
- Poor backup facility: Docker is ineffective if the device fails and the container needs a backup. The backup solution is not automated, and it provides low scalability.
- Not suitable for rich GUI applications: Docker is primarily designed to work with applications based on a command line. It is very tough for Docker to run a graphical interface inside a container, making it unsuitable for applications requiring a rich GUI.
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Which to Choose: Containers or Docker?
Docker has proven to be better than containers as it encapsulates all the requirements an application needs to run successfully in one environment. Docker can also be well integrated with cloud platforms which help users to run the application on any server, PC or laptop.
Additionally, Docker containers are very well-optimised and contain all the prerequisites and libraries required to develop an application in a single platform. Docker consists of multiple system tools, libraries settings etc., that allow the container to run independently.
Use Cases for Containers and Docker
Docker is lightweight and is equipped with the prerequisites of an operating system. Thus, Docker containers are increasingly used in the industry, and the primary use cases are explained as follows:
- Deploying software: Docker containers are packed with all the configurations and dependencies that users may need for deploying applications. This feature makes it easier for the users to transfer files whenever required from PC to a server or otherwise. Even more complicated applications can be deployed with the use of Kubernetes. Register for a Master of Science in Computer Science from LJMU to learn the difference between Docker and Kubernetes and other in-demand software development skills.
- Running lightweight Linux applications: Docker containers are lightweight, and the Docker hub consists of images to run applications. With configurations and installing desired software, Docker users can customise a well-integrated container with the Linux server without impacting the host operating system.
- Hosting servers: Docker containers are robust and can host multiple servers. Docker works with file and web servers and can create reverse proxy servers as and when required.
- Creating a development environment: The development environment comes with complex configuration problems and dependencies. Docker containers help to solve these problems to work on complex projects. As the Docker container comes within the entire package, everything can be done in a single platform, making the workflow easier.
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Conclusion
Docker has captured the containerisation market, and its impact will only increase. But containers have won the constant tussle between the Docker image and container discussion as it provides a complete package to run stand-alone applications. If you want to become a master in this field, consider signing up for the Executive PG Programme in Full Stack Development from IIITB by upGrad. The course will enlighten you about the core concepts of Docker and help you learn how to implement it practically.
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