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Kubernetes Architecture

Kubernetes uses protocols like gRPC or REST. Components like etcd and kube-api-server communicate with each other using gRPC or REST.

Deep Dive into K8S Architecture​

There are 2 types of components:

  1. Control Plane/Master Node
  2. Worker Node/Data Node

Master Node​

The master node consists of 5 main components:

  1. etcd
  2. kube-api-server
  3. kube-scheduler
  4. kube-controller-manager
  5. cloud-controller-manager (for cloud clusters like ECS, EKS)

kube-api-server​

The API server follows this flow: Authentication → Authorization → Admission Control → Watch Updates

Admission Controllers include both Validating and Mutating Admission Controllers:

  • Mutating AC: Checks if the pod is the right size and validates YAML configuration through Object Schema Validation
  • Validating AC: Validates if the pod meets requirements before storing in etcd

Key features:

  • Webhooks: Plugins based on mutating or validation
  • File path: /etc/kubernetes/manifests
  • Custom Resource Definition (CRD): Extends Kubernetes functionality, allowing deployment without manually creating services and ingress

Watch Updates: Monitors for tasks that need to be completed or updated.

etcd​

etcd is the cluster's data store with these characteristics:

  1. NoSQL Database (key-value pair storage)
  2. Raft Consensus algorithm for distributed consistency
  3. Protobuf for data serialization
  4. WAL (Write-Ahead Logging) for data durability

kube-scheduler​

The scheduler is responsible for assigning pods to nodes based on resource requirements and constraints.

kube-controller-manager​

Manages various controllers including:

  • Node Controller: Monitors node health
  • Route Controller: Manages network routes
  • Service Controller: Manages service endpoints
  • CronJob Controller: Handles scheduled jobs

Worker Node​

The worker node consists of 3 main components:

  1. kube-proxy
  2. kubelet
  3. Container Runtime

kube-proxy​

Handles networking for pods on the worker node:

  • Manages daemon sets and iptables rules
  • Handles the networking part of pods
  • Each node has a cluster IP (private IP) for internal communication
  • Creates iptable rules to map services to pods

kubelet​

The primary node agent that:

  • Communicates with the API server
  • Ensures containers are running as expected
  • Reports node and pod status back to the control plane

Container Runtime Interfaces:

  • CRI (Container Runtime Interface): Manages container lifecycle
  • CNI (Container Network Interface): Handles pod networking
  • CSI (Container Storage Interface): Manages persistent stor