Software deployment or shipping used to happen with specific instructions about the prerequisites about the environment (both software and hardware) in which to run it. These were called the dependencies of the software, without which it would not be able to function. However, with the advent of the Internet and Java, a lot of that changed and containers and virtual machines (VM) became common. Apps could be shipped in a form that made it possible to run them anywhere, without any pre-conditions. The virtual machines made it possible to run the executable in an isolated environment, with the use of hypervisors. The hypervisors made it possible for the machines to run VMs by provisioning separate resources for it appropriately.
As Linux started becoming mainstream, the term open-source also started making waves. The developer community realized the need to have some community wherein collaborative and shared development can happen. That is what gave birth to OSI (Open Source International) and the concept of open-source software. All software classified as open-source would make its design available freely for all, to use, modify and enhance as deemed necessary. This would help in rapid prototyping through collaboration and shared resources through a community. Of course, there are open-source licenses in place to regulate the way people can use, study, modify and distribute this software. But they are far more open and meant to increase the collaboration and not restrictive in any sense.
What is a container?
A container can be termed as a software packaging mechanism that will insulate the software from its environment, making it possible to run it in any computing environment. So, the container unit of software would contain all the dependencies required to run the application successfully. Containerization makes development quick as developers can focus only on the application logic, and not worry about the dependencies part. It also makes it possible to deploy applications faster, to any computing environment, as the app would be able to run independently, once deployed.
In a way, containers are like virtual machines; Like virtual machines, containers also provide an isolated environment in which to run the software independently. Both of these run on top of the host operating system. But while VMs abstract the hardware into multiple VMs running on a single machine, containers virtualize the OS, instead of the hardware. The container abstraction is at the app layer and not the hardware layer. Multiple containers can run on the same machine and share the kernel, and yet function independently of each other. Each VM though, is a full copy of the OS, taking up that many resources, making it slow. Containers are lighter and take up lesser space.
Perse, containers are built, run, and managed using some technology. They are built to operate seamlessly, and their runtime management is mostly automated as otherwise, the purpose is defeated. Though containers provide a certain amount of security to the apps purely by their design, this does mean that the apps won’t need any additional security. They ensure consistency and uniformity in the way apps run across environments.
Docker is an open-source container tool that is used to create, deploy, and run applications by using containers. The Docker engine was launched in 2013 and leveraged a lot on Linux. Later, Docker was also extended to Windows and its functionalities are available on Windows Servers as well, called Docker Windows containers. In June 2015, Docker donated the container image specification and runtime code now known as runc, to the Open Container Initiative (OCI) to help establish standardization as the container ecosystem grows and matures.
Docker allows the apps to use the host kernel and they only need to be shipped or deployed with things that are not already running on the host computer. They are, therefore, lightweight, and highly efficient, as they do not require an OS per the application being run. Being open-source, Docker also allows developers to think out of the box, to modify the software to suit their additional needs if any.
Docker is a very useful tool that helps the developers to focus only on their job – development. They need not worry about any other dependencies about the environment where the software will ultimately run on. Also, being open-source software, Docker comes with a lot of pre-written programs that these developers could use as is, or modify to suit their needs. This brings down the development time by a great margin.
This tool has also become a coveted one for the system administrators/DevOps professionals in recent times. Docker provides them with great flexibility in faster deployment and reducing dependencies with its reduced footprint and overhead. Docker has created the industry standard for containers, so they are highly portable. Docker also provides a great amount of security to the apps running in their containers.
The benefits that containers and Docker bring into modern software development can be summarized as below:
Lightweight: Containers share the OS kernel and are therefore lightweight. They are also small in size and use up lesser resources and can scale up faster.
Portability: Without this, perhaps, containers would not have been what they are. Portability is one of the most important benefits that containers bring in through the removal of dependencies.
Speed: Modern software development is often termed as agile. This means rapid development with aggressive deadlines and multiple deployments within a short period. Dockers and containers make this possible by empowering the developers to concentrate on their work, and system admins and DevOps professionals to deploy with agility. Also, the smaller size, and portability too, add on to the speed of deployment. The Continuous Integration and Deployment (CI/CD) model of DevOps is dependent on container models.
Suited for most architecture: Since a lot of apps nowadays run on microservices architecture, container apps are well suited for such environments. Container apps are also well suited for most forms of Cloud deployment, like even hybrid Clouds.
Migration: Containerizing apps are now the most common method for migrating apps to modernize them, and bring in better manageability and portability. Containers provide much-needed flexibility to scale the apps and services. Also, containers allow migration without the need for having to re-architect these apps, which could be a herculean as well as an expensive task.