The Ultimate Guide to Docker Images: Creation, Containers, Advantages, Disadvantages, and Real-Time Use Cases

Understand Docker images ?

A Docker image is a file used to execute code in a Docker container. Docker images act as a set of instructions to build a Docker container, such as a template. Docker images also act as the starting point when using Docker. An image is comparable to a snapshot in virtual machine (VM) environments. 

 Docker is an open source project that's used to create, run and deploy applications in containers. A Docker image contains application code, libraries, tools, dependencies and other files needed to make an application run. When a user runs an image, it can become one or many instances of a container. A Docker daemon operates in the background to oversee images, containers and related tasks. Communication between a client and the daemon is facilitated through sockets or a RESTful API.

Docker image use cases 

A docker image provides a wide range of use cases which provide the following benefits:

• Development and deployment efficiency : A Docker image has everything needed to run a containerized application, including code, config files, environment variables, libraries and runtimes. When the image is deployed to a Docker environment, it can be executed as a Docker container. The docker run command creates a container from a specific image.
• Consistency : Docker offers a consistent environment for applications, letting them function consistently across all environments from development to production. Also, Docker's parity feature ensures that images function the same regardless of the server or laptop they're running on, which saves time when configuring environments and troubleshooting issues that are unique to each one.
• Platform independence : A Docker image is a cross-platform image. For example, it can be created in the Windows environment, submitted to the Docker hub and fetched by users running linux and other operating systems (OSes).
• Portability : Docker images are lightweight, small and fast, which makes them extremely portable across all different versions of Linux, laptops or the cloud.
• Reusability : Docker images are a reusable asset deployable on any host. Developers can take the static image layers from one project and use them in another. This saves the user time because they don't have to recreate an image from scratch.
• Scalability : By spinning up several instances of containers, Docker images facilitate easy horizontal application scaling. With the use of orchestration and management options such as docker swarm or kubernetes, organizations can automate load balancing and scaling in response to demand.

Docker container

• A Docker container is a virtualized runtime environment used in application development.
• It's used to create, run and deploy applications that are isolated from the underlying hardware.
• A Docker container can use one machine, share its kernel and virtualize the OS to run more isolated processes. As a result, Docker containers are lightweight.
• Docker containers can be scaled rapidly to meet the demands of a changing workload. This makes them suitable for microservices architectures and cloud-native applications.

Docker image

• A Docker image is similar to a snapshot in other types of VM environments. It's a record of a Docker container at a specific point in time.
• Docker images are also immutable. While they can't be changed, they can be duplicated, shared or deleted. This feature is useful for testing new software or configurations because whatever happens, the image remains unchanged.
• Containers are dependent on Docker images and need a runable image to exist because images are used to construct runtime environments and are needed to run an application.
• Docker images are created with the build command and are housed in a Docker registry. Because of their layered structure where multiple layers of images are built upon one another, they require minimal data transfer across networks.

How to create a Docker image

Docker images can be created using either an interactive or Dockerfile method.

Interactive method :

The interactive method is the easiest way to create docker images. With this method, users run a container from an existing Docker image and manually make any needed changes to the environment before saving the image. This approach is useful for scenarios where a more hands-on, live approach to image creation is preferred, enabling direct manipulation and customization of the container environment.

The following steps are involved in creating a Docker image:

1. Launch Docker and open a terminal session.
2. Use the Docker run command image_name:tag_name. This starts a shell session with the container that was launched from the image. If the tag name is omitted, Docker uses the most recent version of the image.
3. After this, the image should appear listed in results.

Dockerfile method :

A Dockerfile is a text-based file with no file extension that contains a script of instructions Docker uses to build a container image. This process is more difficult and time-consuming, but it does well in continuous delivery environments. The method includes creating the Dockerfile and adding the commands needed for the image.

The following are the steps involved in creating a Docker image:

1. Once the Dockerfile is started, the user sets up a .dockerignore file to exclude any files not needed for the final build. The .dockerignore file is in the root directory.
2. The Docker build command is used to create a Docker image, and an image name and tag are set.
3. The Docker images command is used to see the created image.

Advantage and disadvantage of docker image:

Advantages of Docker Images:

• Portability and Consistency:

Docker images allow applications to be packaged and deployed consistently across different environments, ensuring that they run the same way regardless of the underlying infrastructure.

• Resource Efficiency:

Docker containers are lightweight, requiring minimal storage space and resources compared to traditional virtual machines, allowing for more efficient resource utilization.

• Fast Deployment:

Docker images simplify and speed up the deployment process, enabling rapid and repeatable application deployments.

• Scalability:

Docker facilitates application scalability by enabling the creation of multiple instances of a container and distributing the workload efficiently using container orchestration tools like Kubernetes.

Disadvantages of Docker Images:

• Security Concerns:

While Docker provides isolation between containers, it's not immune to security vulnerabilities. Shared kernel dependencies and the potential for privilege escalation pose security risks, especially in multi-tenant environments.

• Complexity:

Managing a large number of containers and their dependencies can become complex, requiring careful planning and orchestration.

• Limited Orchestration:

While Docker is excellent for containerizing applications, it lacks built-in orchestration capabilities for managing and scaling containerized applications at scale, requiring tools like Kubernetes or Docker Swarm.

• Persistent Storage Management:

Managing stateful applications in containers can be problematic, as containers are designed to be ephemeral, and data persistence requires careful planning and implementation.

Docker image commands

There are sets of primary docker image commands, categorized as child commands; some include the following:

• docker image build : Builds an image from a Dockerfile.
• docker image inspect : Displays information on one or more images.
• docker image load : Loads an image from a tar archive or streams                      for receiving or reading input. This also known as STDIN.
• docker image prune : Removes unused images.
• docker image pull : Pulls an image or a repository from a registry.
• docker image push : Pushes an image or a repository to a registry.
• docker image rm : Removes one or more images.
• docker image save : Saves one or more images to a tar archive and                    is streamed to normal output, or STDOUT, by default.
• docker image tag : Creates a tag TARGET_IMAGE that refers                                 to  SOURCE_IMAGE.

The Docker CLI provides commands that are used to customize Docker images. Examples of Docker image commands include the following:

• docker image history : Shows the history of an image, including                                   changes made to it and its layers.
• docker update : Updates the configuration of containers.
• docker tag : Creates a tag, such as TARGET_IMAGE, to group and                        organize container images.
• docker search : Looks in Docker Hub for whatever the user needs.
• docker save : Saves images to an archive.
• docker compose : Handles an environment variable.

Conclusion

In conclusion, Docker images allow developers and system administrators to package and deploy applications in a uniform and portable manner. Images are a powerful technique for building, sharing, and running programs across different environments because they use a layered file system and a declarative approach via Dockerfiles.