Hello Readers, Welcome back !

Lets talk about Kubernetes & start from the scratch. #Beginners

Kubernetes: It is a portable, extensible, open-source platform for managing containerized workloads and services. It has a large, rapidly growing ecosystem. Kubernetes services, support, and tools are widely available.

Container: A container is a ready-to-run software package, containing everything needed to run an application: the code and any runtime it requires, application and system libraries, and default values for any essential settings.

Nodes: A node is a machine either physical or virtual machine on which Kubernetes is installed. A node is a worker machine and this is where containers inside the pods will be launched by Kubernetes.

Pod: A pod is the smallest deployable unit that can be managed by Kubernetes. A pod is a logical group of one or more containers that share the same IP address and port space. The main purpose of a pod is to support co-located processes, such as an application server and its local cache.

Master Node: (aka Control Plane)

• The Master node (Brain) manages the worker nodes (Body) and the Pods in the cluster.
• Its components are as depicted in the diagram ( ETCD, Kube-apiserver, Kube-scheduler etc )
• The master makes global decisions about the cluster and they also detect and respond to cluster events like starting up a new pod when a deployment's field "replicas" is unsatisfied. (replicas dictate the number of identical structures of nodes to be kept at any given point in time)
• Master components, set up scripts typically start all master components on the same machine, and do not run user containers on this machine for the sake of simplicity.

Worker Node:

• The worker nodes are the part of the Kubernetes clusters which actually execute the containers and applications on them.
• These worker nodes have docker containers for each application running on them. There may be a different number of containers running on each node depending on the distribution of the workload.
• Worker nodes are generally more powerful than master nodes because they have to run hundreds of clusters on them.
• However, master nodes hold more significance because they manage the distribution of workload and the state of the cluster.

ETCD:

• It is a distributed reliable key-value store(database) that is easy to install, secure, persistence, highly available & fast.
• Its used to store & retrieve small bit of cluster data which requires fast read & write.
• Its not a traditional/relational database rather a Key-value format database store.
• It stores information regarding the cluster i.e., Nodes, PODs, Secrets, Configs, Roles, Accounts etc.
• Installation - Download Binaries -> Extract -> Run ETCD Service.
• Default port 2379 & Default client etcdctl.
• ETCDCTL is the CLI tool used to interact with ETCD.

KUBE CONTROLLER:

• It manages various controllers & it has its own set of responsibilities.
• It is a process which continuously monitors the state of components & works towards bringing the cluster to desired state.
• There are ample amount of controllers such as Deployment, Replica set, Endpoint, Job, Node, Namespace etc.
• Logically, each controller is a separate process, but to reduce complexity, they are all compiled into a single binary and run in a single process.
• It is similar to our "police department", which continuously checks the status of the city & takes action to remediate the situation accordingly.

KUBE-APISERVER:

• It is a primary management component in Kubernetes.
• The API server is a component of the Kubernetes master node (Control Plane) that exposes the Kubernetes API.
• It authenticates user, validates requests + retrieves & updates data from ETCD Cluster.
• kubectl is used to communicate with kube-apiserver or we can invoke api directly by sending a POST method request.

KUBE-SCHEDULER:

• It is only responsible for deciding which pod goes on which node.
• Which get decided on certain criterion ( CPU, Memory etc )
• Firstly scheduler tries to filter out the nodes that do not fit for pod.
• Secondly it give priority to nodes having optimal resource usage.
• REMEMBER "It does not actually place the pod on the nodes"

KUBELET:

• An agent that runs on each node in the cluster & also makes sure that containers are running in a POD. #Informer
• The kubelet in the worker node, registers the node with the kubernetes cluster.
• The kubelet continues to monitor the state of the POD and the containers in it and reports to the kube-apiserver on a timely basis.
• The kubelet doesn't manage containers which were not created by Kubernetes.

KUBE-PROXY:

• kube-proxy is a network proxy that runs on each node in your cluster.
• Its job is to look for new services and every time a new service is created it creates the appropriate rules on each node to forward traffic to those services to the backend pods.
• kube-proxy maintains network rules on nodes.
• These network rules allow network communication to your PODs from network sessions inside or outside of your cluster.
• One way it does this is using IPTABLES rules.

#aws #community #opensource #K8s #EKS #docker #computing

You can reach out to me @ linkedin.com/in/kunal-shah07

In the next article I'll try to jump into the depth of kubernetes.

Until then, Keep learning :)

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