You may be familiar with Docker containers and have even used them a few times. However, you might be curious about the practical applications of Docker containers beyond simply running basic commands like "docker run redis". So, let's explore the broader uses of containers and how they can benefit your projects and applications in this article.

The Benefits of Using Containers
Containers serve the purpose of packing an application and its dependencies into a self-contained environment, ensuring isolation, predictability, and repeatability in execution. While virtual machines offer similar functionalities, they require more time for creation, configuration, shipping, and execution. Containers, on the other hand, provide all these advantages while being significantly faster and lighter in comparison with VMs

To better comprehend the various use cases for Docker containers, it is essential to review their characteristics and why they are integral to DevOps practices. By grasping the advantages of containers, we can appreciate why they excel in the specific use cases we will explore below.

Containers provide the following advantages:

• Unified packaging: Docker containers encompass all the necessary components of an application, including binaries, dependencies, and libraries. This eliminates the need for an installation process.
• Consistent execution: A container image runs consistently regardless of the environment it is deployed in. Once an application is built as a Docker image, it can be executed on any system with Docker installed. Multiple instances of the application can be effortlessly launched, ensuring consistent behavior across all instances.
• Efficiency: Containers are lightweight, and are fast to create or destroy. This facilitates seamless software upgrades and patches. Rather than modifying or upgrading an application within a running container, a new container with the updated application can be launched, replacing the old one.
  Moreover, Docker images are composed of layered structures, enabling efficient image transfer as Docker only needs to download the missing layers.
• Portability: Docker ensures portability through its image format, similar to a compressed file (specifically, a TAR archive). This format encapsulates the entire application and its dependencies. Docker images can be downloaded from public or private registries or created independently. Containers run consistently across different environments, whether it be a laptop, data center, or public cloud.
• Isolation: Docker containers offer a level of isolation, creating a sealed environment for each application. Running an application within a container prevents it from impacting other applications, unless explicitly configured to do so.
  Containers vs Virtual Machines

Virtual machines share similar benefits to those mentioned above, but containers offer a more streamlined level of virtualization. Unlike virtual machines that virtualize an entire operating system, containers virtualize individual processes. As a result, containers provide a few outstanding advantages over VMs:

• Efficiency: Containers, virtualizing a single process, are lightweight and facilitate easier distribution compared to virtual machines. They consume fewer resources, have faster startup times, and are more scalable than VMs.
• Composability: Due to their lightweight nature, containers can be easily stacked and interchanged. This feature is particularly advantageous in microservice architectures, which consist of numerous self-contained services managed independently. Containers serve as an excellent technology for achieving this level of composability.

Use Cases for Containers
To fully comprehend the purpose and practical applications of a technology, it's essential to understand its real-world applications. Let's explore the primary areas where containers are widely employed in various industries and scenarios.

1. Running third-party applications and utilities
Numerous popular applications are readily available as container images. It's possible that an application you frequently utilize can be found as a Docker image.

Let's take a look at a few examples of applications that are accessible on Docker Hub, one of the primary registries where Docker images can be discovered and downloaded:

• PostgreSQL (a database)
• Python (the programming language)
• Ubuntu (Linux operating system)
• Nginx (web server).

The advantages of using these containerized applications are significant. They come packaged in a standardized manner, inclusive of all their dependencies, and exhibit consistent behavior regardless of the environment in which they are executed. By leveraging containerization, you can bypass the challenges associated with manual installation or configuration of these applications.

2. Deploying software to a cloud platform
Cloud platforms like Kubernetes, and OpenShift fully support containers. This is highly advantageous for both platform administrators and developers, as it establishes a standardized packaging format for building and running applications on these platforms.

Platform administrators no longer need to delve into the complexities of various application servers and their associated libraries, while developers are relieved from the burden of comprehending a wide range of virtualization technologies. Consequently, PaaS (platforms-as-a-service) have widely embraced containers, particularly Docker, due to the inherent advantages they offer.

From a developer's perspective, the true benefit lies in the ability to package an application, along with all its dependencies, into a well-known and portable format: the container image. Upon arrival on the platform, administrators can effortlessly execute the application because it adheres to the Docker (or OCI) standard.

Previously, deploying applications posed challenges as they were done through diverse methods like scripts, installers, or even on virtual machines. However, containers have introduced a standardized API that both developers and system administrators comprehend.

This parallels the concept of how applications operate on Apple and Android app stores. Developers package their applications using a standardized approach, and the mobile operating systems understand how to unpack and execute those applications, all thanks to the adoption of a common format.

For example, Kubernetes, an open-source container platform, leverages containers to execute applications effectively. Consequently, to deploy an application on Kubernetes, it typically needs to be packaged within a container. Kubernetes can retrieve the container image from a registry, allocate it to a node within the cluster, and initiate the container. This capability stems from the fact that a Docker container adheres to a standard format known as OCI (Open Container Initiative). Therefore, Kubernetes doesn't require extensive knowledge about the container's internal components or the specific procedure for launching the program within it.

3. Running dependencies during development and testing
When developing software, many individuals begin their journey with containers using Docker. Docker enables users to execute one or more dependencies of their application. Frequently, a substantial amount of time is wasted on installing and configuring the necessary dependencies for an application. Most applications rely on additional components, such as databases or APIs, to function.

Consider the instances when you needed to work with a database while developing an application. It often entails downloading the dependency and going through the configuration process, which can be time-consuming. For example, setting up complex software like Oracle Database could take a significant amount of effort, despite only requiring a few days of actual development time.

However, if your application relies on a dependency that has been packaged as a Docker image, you can effortlessly pull the image from a registry, run the container, and instantly have an instance of your dependency ready to use. This eliminates the need for extensive installation and configuration, allowing you to focus on developing your application promptly.

4. Compiling software predictably
During software development, the compilation or packaging of your code is often necessary, particularly for languages like Java or C. While this may appear to be a straightforward task, the tools required for compiling your program can occupy a significant amount of disk space, often reaching hundreds of megabytes, and require proper configuration, adding to the complexity.

Compiling software involves installing and setting up specific compilers, libraries, and build tools, which can be time-consuming and prone to errors. Additionally, ensuring compatibility and consistency across different development environments further complicates the process.

However, with the use of containers, you can simplify this task. By packaging the necessary compilers, libraries, and build tools into a container image, you can easily reproduce the development environment on any machine that supports Docker. This eliminates the need for extensive manual setup and reduces the chances of compatibility issues. With a containerized development environment, compiling and packaging your software becomes a more streamlined and efficient process, allowing you to focus on writing code rather than struggling with configuration complexities.

Containers make the process much simpler. To begin, you create a container image for your build environment, which includes all the necessary dependencies for building your software. When it's time to build your code, you can easily mount your code into the build container and initiate the compilation process. Each build takes place in a clean instance of the build container, ensuring more predictable and consistent results.

By using containers for building software, you can avoid issues related to conflicting dependencies or differences in development environments. Every build occurs in an isolated and reproducible environment, guaranteeing that your builds are reliable and consistent across different machines and development setups. This streamlined approach saves you time and effort, allowing you to focus on developing your software without worrying about complex build configurations.

For example, to build a Java app using containers, you can use the Maven Docker image for compiling the source code. Then, you can copy the compiled code into a separate container with the Java runtime environment based on the OpenJDK image. This ensures a streamlined and repeatable process for building Java applications.

5. Running an application in different environments
Docker enables consistent application execution across environments. The standardized API offered by container engines, such as Docker, ensures that a container behaves predictably on any machine. Whether it's running on my personal computer or another system, the container maintains its consistent behavior.

Running a container is typically as easy as using the "docker run" command. This simplicity makes containers a valuable approach for deploying applications across various environments while ensuring consistency. By creating a single container image and running it in different environments with slight configuration variations, you can achieve parity between them.

Even if containers are not utilized for production environments, they still serve as a highly valuable method for sharing applications across different environments (e.g. dev, test, UAT). This allows for predictable and consistent application sharing across the various stages of the development lifecycle.

For example, containers can serve as a convenient method to transition an application from development to testing. Developers package their code into a container or Docker image and deliver it to the testing team. The testing team can effortlessly run the container image without the need for intricate steps, server configuration, or virtual machine creation. By utilizing the "docker run" command, the testing team can easily start the containerized application, enabling them to perform thorough testing and evaluation. This streamlined process eliminates complexities and allows for efficient testing of the application.

Conclusion
In conclusion, containers offer a wide range of practical use cases that benefit developers, testers, and platform administrators alike. By utilizing containers, you can easily manage application dependencies, create consistent build environments, seamlessly move applications between different environments, deploy applications on cloud platforms, and run utilities or programs without extensive upfront installation and configuration.

The key characteristics of containers, including portability, isolation, and repeatability, tie all of these use cases together. These characteristics enable developers and teams to work more efficiently, reduce complexity, and ensure consistent application behavior across various environments.

As containers continue to gain popularity, we can expect to witness even more innovative use cases emerging in the software development field. It is an exciting time for you to be part of this technological revolution and seize the opportunities that containers offer in innovative ways.