Note_Tech

All technological notes.

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Kubernetes Cluster - Architecture

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• Kubernetes Cluster - Architecture
  • Architecture
    • Node and Cluster
    • Components
  • Master Machine Components
  • Node Components

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Architecture

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Node and Cluster

• Node / Minions

  • A machine, physical or virtual, that provides the resources required to run workloads.

• Worker Node

  • A type of node that runs the application workloads (pods) and provides compute, storage, and networking.

• Master Node / Control Plane Node

  • A type of node that runs the control plane components responsible for scheduling, orchestrating, and monitoring workloads across worker nodes.

• Cluster

  • A collection of nodes, master and worker, that operate together as a single system for running and managing applications.

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Components

• API Server
  • the front-end for kubernetes
  • The users, management devices, Command line interfaces all talk to the API server to interact with the kubernetes cluster.
• ETCD service
  • a distributed reliable key-value store used by kubernetesto store all data used to manage the cluster.
  • stores all that information on all the nodes in the cluster in a distributed manner
  • responsible for implementing locks within the cluster to ensure there are no conflicts between the Masters.
• A kubelet service
  • agent that runs on each node in the cluster.
  • responsible for making sure that the containers are running on the nodes as expected.
• A Container Runtime
  • the underlying software that is used to run containers.
  • example: docker

• Controllers

  • responsible for noticing and responding when nodes, containers or endpoints goes down.
  • The controllers makes decisions to bring up new containers in such cases.
• Schedulers
  • s responsible for distributing work or containers across multiple nodes.
  • looks for newly created containers and assigns them to Nodes.

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Master Machine Components

• Control Plane Components

  • Manage the overall state of the cluster

• etcd

  • a distributed, key-value store that Kubernetes uses as its primary datastore.
  • used to stores the configuration information which can be used by each of the nodes in the cluster.
  • distributed among multiple nodes.
  • accessible only by Kubernetes API server as it may have some sensitive information.

• API Server

  • a control plane component that serves as the central point of access for interacting with the cluster
  • a RESTful API over HTTP, enabling users, other cluster components, and external systems to manage, query, and manipulate the state of Kubernetes objects like Pods, Services, and Deployments.

• Controller Manager

  • a control plane component used to run controller processes.
  • a daemon which runs in nonterminating loop and is responsible for collecting and sending information to API server.
  • To get the shared state of cluster and then change the current status of the server to the desired state.
  • key controllers
    • replication controller,
    • endpoint controller,
    • namespace controller,
    • and service account controller.

• Scheduler

  • a control plane component used to allocate Pods to Nodes in the cluster and distribute the workload.
  • To track utilization of working load on cluster nodes and then place the workload on which resources are available and accept the workload.
  • Default scheduler: kube-scheduler.

• cloud controller manager

  • A control plane component that embeds cloud-specific control logic.
  • Optional component.

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Node Components

• Container runtime

  • A node component that empowers Kubernetes to run containers effectively.
  • To manage the execution and lifecycle of containers within the Kubernetes environment.

• kubelet

  • An agent that runs on each node in the cluster.
  • To ensure that containers are running in a Pod.
    • relay information to and from control plane service.
    • interact with etcd store to read configuration details and wright values.
    • receive commands and work.
    • manage network rules, port forwarding, etc.

• kube proxy

  • a network proxy that runs on each node in cluster, implementing the Kubernetes Service.
  • forward the request to correct containers
  • perform primitive load balancing
  • maintains network rules on nodes.
  • optional