The container allows the application to work in almost any environment, providing quick deployments and reproducible builds. Containers allow us to run applications on non-native OS, for example, Linux applications on Windows or macOS.
What are containers?
We call technology the container technology if it allows using the running processes of applications and their dependencies in isolation. Container technology simplifies builds of production-ready applications and provides high-level tools to create a piece of software packed with all dependencies.
The most significant feature of containers is isolation. Various dependencies, libraries, and files of the applications are packed into a container. In this way, the application that works in one place can work in any environment. Different configurations of the same application become available with environment variables.
Multiple containers can run on a machine with the host's operating system isolated in the core. In short, containers can handle any task, despite their small size, and eliminate the need to purchase extra storage space.
Examples of container management software are Docker, Google Kubernetes Engine, Microsoft AKS, AWS Fargate.
What problems do containers solve?
Containers help us overcome such problems as:
Missing libraries, different versions of different applications, or incorrect application dependencies.
Port conflicts between programs running on the same computer.
Overuse of processor and memory-style resources by an application.
The difficulty of installing, starting, stopping, and uninstalling applications.
How do they do it?
To understand how the containers do such tasks, let's dig into their internals.
The three pillars of container technology are namespaces, control groups, and union file systems. Namespaces provide their own view of the underlying Linux system by limiting what containers can see and access. When you run a container, containers create namespaces that the particular container will use and have multiple namespaces that present different information about the operating system. For example, the MNT namespace limits the mounted file systems a container can use, or the USER namespace is used to isolate users in each container.
Control groups are also called cgroups. It is a Linux kernel feature that isolates, prioritizes, and calculates the resource usage (CPU, memory, disk I/O, network, etc.) of a set of processes. Control groups can also impose strict limits on usage, ensure that containers use only the resources they need and, if necessary, set limits on the resources a container can use.
Isolated Union file systems used in containers are stackable. This system helps avoid duplication of data every time you deploy a new container.
What are the advantages of containers?
Containers have many advantages. They also have been preferred by quite a lot of users in recent years. So what are the advantages of containers?
Deploying an existing service with containers takes just a few clicks or commands. On the other hand, you'll probably need to learn how to configure containers properly which takes time and practice.
With the file describing the content of a container, we can start new containers or create more containers with already running applications with just a few commands.
A consistent test environment is provided by following a certain pipeline when using containers.
Thanks to the mass spread of container and cloud technologies, companies can deploy their software almost in any cloud provider with ease.
Conclusion
In summary, containers become more popular every year, because making things lighter and faster. What you will learn in this topic and the upcoming topics will be useful in all areas of software development, as containers are becoming more and more common.