What is the difference between cluster and container?

What is a container?

Container solves the problem of running the same application across multiple operating systems without running into unexpected errors. A software container is responsible for packing up an application or service and all its dependencies, libraries, and code in a single place. The major difference between a container and a virtual machine is that, unlike VMs, containers don’t need to create a whole virtual operating system. Containers allow applications to use the Linux kernel they are running on.

Use of Container

With the immense popularity of microservices architecture, nowadays, organizations have started leveraging multiple containers running on multiple machines. Dedicated container orchestration tools are used to manage these containers better. Let’s have a look at a few of the common ways organizations are using containers -

• Lift and Shift: Few organizations leverage containers to migrate their existing applications into more modern environments. However this practice
• Refactoring of existing applications: Refactoring is a process of porting existing monolithic applications into container-based applications.
• Develop container-native applications: Organizations also use containers to develop fully container-native applications from scratch. Just like refactoring, this approach also unlocks the full benefits of containers.
• Easier deployment of repetitive jobs: Containers are meant to be run in the background and work flawlessly in supporting ETL functions or batch jobs.
• Helps support DevOps for CI/CD: Container technology supports streamlined build, test, and deployment from the same container images.

What is a cluster?

A Kubernetes cluster is a collection of nodes that work together to run containerized applications. Containerizing encapsulates an app’s dependencies as well as some essential services. They are lighter and more adaptable than virtual machines. Kubernetes clusters make it easier to develop, migrate, and manage apps in this way.

Containers can run on multiple machines and environments using Kubernetes clusters. Unlike virtual machines, Kubernetes containers are not limited to a single operating system. Instead, they can share operating systems and execute from any location.

What is a cluster made up of?

A Kubernetes cluster is composed of six main components, namely -

1. API server: Serves as the front end of the Kubernetes control panel. API servers are responsible for exposing the REST interface of all Kubernetes resources.
2. Scheduler: Based on resource requirements and metrics, containers are placed. The scheduler also identifies pods with no node assigned and selects nodes for them to run on.
3. Controller manager: It manages all the controllers such as node controllers, endpoint controllers, and replication controllers.
4. Kubelet: Interacts with the Docker engine for creating and managing containers to ensure that containers are executing in a Pod. Takes a set of PodSpecs and guarantees that the containers that correspond to them are completely operational.
5. Kube-proxy: Responsible for managing network connectivity and maintaining network rules across every node in the given cluster.
6. Etcd: Kubernetes store for storing all the cluster data.

Use of cluster

Thanks to Kubernetes clusters, containers may run on a variety of devices and contexts, including virtual, physical, cloud-based, and on-premises. Unlike virtual machines, Kubernetes containers are not bound to a particular operating system. Instead, they may run everywhere and share operating systems. One can create a kubernetes cluster by using an open-source tool known as Minikube. It is compatible with windows, mac and linux. Minikube is used to create simple streamlined cluster that contains only one working node.

A Kubernetes cluster contains one master node and a few worker nodes. Depending on the cluster, these nodes can be actual computers or virtual ones.

The master node is responsible for controlling the state of the cluster. It coordinates the process such as -

1. Scheduling and scaling applications
2. Maintaining a cluster’s state
3. Implementing updates

The worker node, on the other hand, performs tasks assigned by the master node. A minimum of one master and one worker node is compulsory for a kubernetes cluster to be operational. While in production and staging, cluster is distributed across different worker nodes.

Relation between Cluster and Container

Containers and clusters are both part of Kubernetes. There is a symbiotic relationship between the two. A container logically runs inside a pod. A group of many pods, whether related or unrelated to each other, forms a cluster. Both container and cluster are distinct things yet are dependent on each other.

Containers have eliminated application deployment burdens. As application is isolated from its host and dependencies are packed within the container, security is also improved. Your web application’s availability, scalability, and performance can be greatly enhanced by deploying containerized apps across cluster nodes. Running several containers on a single node maximises resource utilization, and ensures that each container is running in more than one instance at once. This prevents the creation of a single point of failure for your application.