Containers have turn into a major trend in the development of software as an alternative to Virtual Machine. Containerization assists developers to build and deploy applications more securely and faster. The main use of Containers is for deploying Microservices applications quickly and easily. Without speaking about containers, it’s difficult to speak about microservices.
What is a Container?
A Container is just like a software package into a logical box with all information that the application requires to run. The software package contains an operating system, system tools, system libraries, application code, and binaries and etc.
Containers directly run within the kernels of the Host machine. Containers share the resources of the Host machine (like CPU, Memory, disks and etc.) and don’t require the more load of a Hypervisor. That is why Containers are “lightweight“. The size of Containers is much smaller than a Virtual machine, they require less time to start.
Why Do We Need Containers?
The main benefit of a container is that it is portable and lightweight and, therefore, assists the developer a lot in building and deploying applications. There are many causes for employing Containers however only a few of them are stated below:
Containers share the kernel of OS and thus there is no need for a full Operating System instance per application. It sorts the container files smaller which is why the size of Containers is smaller. As containers are lightweight, they can be horizontally scaled easily.
A Container is a package having all its dependencies within it, which means that we have to build and write the software just once and the same software can be run across diverse systems without the requirement of configuring the complete software again.
Due to their small size and deployment portability across platforms, containers are stated as an ideal fit for application patterns and modern development (such as DevOps).
Containers allow developers and operators to enhance the CPU and memory use of physical machines.
Different Types of Containers
The precise development and growth in container technology take a large set of selections to choose from. There are many types of containers out of which more important and more famous are described below;
Docker is widely used and one of the most popular container platforms. It allows the construction and use of Linux containers. Docker is a tool that sorts the development, deployment, and running of applications very easily by means of containers. Docker is not only embraced by the Linux powers (such as Red Hat and Canonical) but other information technology companies like Microsoft, Oracle, and Amazon, have also accepted it. Today, almost all Information Technology and cloud-based companies have adopted Docker.
Read more about docker https://blogs.slimlogix.com/a-deep-introduction-of-docker-and-its-architecture/
An open-source LXC is the project of Linux Containers. The purpose of LXC is to arrange for isolated application surroundings that closely similar to virtual machines. LXC obeys the process model of UNIX, where there is no central daemon. So, instead of being accomplished by one central package, each container works as if it’s run and managed by an isolated program.
CRI-O is an implementation of the Kubernetes CRI (Container Runtime Interface) to allow using Open Container Initiative (OCI) compatible runtimes. CRI-O is an open-source tool and its aim is to exchange Docker, as the Container engine, for Kubernetes.
The rkt has a set of assisted tools and community to competing Docker. It is also known as Rocket, an upturn from CoreOS to decrease security risk in initial versions of Docker. It is an application container engine build for advanced invention cloud-native surroundings. It sorts a pod-native method, a pluggable implementation environment, and a distinct surface area that marks it perfect for integration with other systems.
The Pod is the core execution unit of rkt, it is a collection of one or more applications running in a shared context. rkt enables consumers to put on diverse configurations. Structural design of rkt means that each pod runs directly in the classic UNIX process model, in an isolated and self-contained environment.
Podman is an open-source container engine, the behavior of podman is more similar to the Docker engine. But the difference between podman and docker is the way in which both work. Like LXC and rkt, there is not a central daemon but Docker obeys the client/server model which is, using a daemon to handle all containers.
In Docker, if the daemon stuck off, we also unable to control the containers. But in Podman, containers are independent, entirely isolated environments, which we can handle independently of one another. More, Docker allows, by default, root permission to the container user, whereas non-root privilege is standard in Podman. In all, these user privilege and isolation characteristics make Podman more protected.
runC is a lightweight OS container. Initially, it was a low-level Docker component, which operated under the hood rooted within the platform structural design. On the other hand, it has been rolled out as a separate modular tool. The indication behind the release was to raise the portability of containers by giving an identical interoperable container runtime that be able to toil both as part of Docker and separately of Docker in another container system. So, runC can aid you to escape being muscularly tied to particular technologies.
Basically, containerd is just like a daemon, supported by both Windows and Linux that turns as an interface between container runtimes and container engine. It offers an absorbing layer that makes it cooler to manage and handle container lifecycles such as container execution, image transfer, snapshot, functionality and specific storage operations, by means of simple API requests.