DevOps

Kubernetes Components Cheatsheet

Comprehensive reference for Kubernetes components covering Control Plane (API Server, etcd, Scheduler, Controllers), Worker Nodes (Kubelet, Kube-Proxy, Pods), Kubernetes Extensions, and kubectl command reference.

#kubernetes #k8s #containers #orchestration #devops #cloud-native
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K8s

What is Kubernetes?

Kubernetes (K8s) is an open-source container orchestration platform that automates the deployment, scaling, and management of containerized applications. It groups containers into logical units for easy management and discovery. When choosing a VPS provider for Kubernetes, consider performance benchmarks to ensure optimal cluster performance.

Control Plane
Manages cluster state and orchestration
Worker Nodes
Run containerized applications in pods
Extensions
Additional features and monitoring

Table of Contents

1. Kubernetes Architecture 2. Control Plane Components 3. Worker Node Components 4. Kubernetes Extensions 5. kubectl Commands 6. Kubernetes Resources

Kubernetes Architecture

Kubernetes follows a master-worker architecture with three main layers: Kubernetes Extensions at the top, Control Plane in the middle, and Worker Nodes at the bottom. This layered architecture enables efficient container orchestration at scale. For production deployments, you can compare different VPS providers to find the best infrastructure for your Kubernetes clusters.

Architecture Layers

Layer 3
Kubernetes Extensions
Web Admin UI, DNS, CLI (kubectl), Container Resource Monitoring
Layer 2
Control Plane
Kube-API Server, etcd, Kube-Scheduler, Controllers (Kube-Controller-Manager, Cloud-Controller-Manager)
Layer 1
Worker Nodes
Pods (Containers), Container Runtime (Docker), Kubelet, Kube-Proxy

Control Plane Components

The Control Plane makes global decisions about the cluster (scheduling, detecting and responding to cluster events). Control Plane components can run on any machine in the cluster, but typically run on dedicated master nodes.

API

Kube-API Server

Central management interface for the entire cluster

The API server is the front end for the Kubernetes control plane. It exposes the Kubernetes API and is the primary interface for cluster management. All operations go through the API server.

Key Functions:
  • • Processes and validates REST requests
  • • Updates corresponding objects in etcd
  • • Acts as gateway for cluster operations
  • • Handles authentication and authorization
DB

etcd

Distributed key-value store for all cluster data

Consistent and highly-available key-value store used as Kubernetes' backing store for all cluster data. Stores configuration data, state, and metadata.

Key Functions:
  • • Stores cluster state and configuration
  • • Provides distributed consensus (Raft algorithm)
  • • Ensures data consistency across cluster
  • • Supports snapshot and restore capabilities
SCH

Kube-Scheduler

Assigns newly created pods to nodes

Watches for newly created pods with no assigned node and selects a node for them to run on. Scheduling decisions consider resource requirements, constraints, affinity/anti-affinity, data locality, and workload interference.

Scheduling Factors:
CTL

Kube-Controller-Manager

Runs controller processes

Runs controller processes that watch the shared state of the cluster through the API server and make changes to move the current state towards the desired state.

Built-in Controllers:
Node Controller Replication Controller Endpoints Controller Service Account Controller Job Controller Namespace Controller
CCM

Cloud-Controller-Manager

Links cluster to cloud provider's API

Embeds cloud-specific control logic. Lets you link your cluster into your cloud provider's API and separates components that interact with the cloud platform from components that only interact with your cluster.

Cloud Controllers:
  • • Node Controller: Checks cloud provider for node status
  • • Route Controller: Sets up routes in cloud infrastructure
  • • Service Controller: Creates/deletes cloud load balancers

Worker Node Components

Worker Nodes maintain running pods and provide the Kubernetes runtime environment. Each node runs the necessary services to run pods and is managed by the Control Plane.

Pod

Pods

Smallest deployable units in Kubernetes

A Pod represents a set of running containers on your cluster. Pods are the basic execution unit of a Kubernetes application and can contain one or more containers that share storage and network resources.

Pod Features:
  • • Single IP address shared by all containers
  • • Shared storage volumes
  • • Shared network namespace
  • • Ephemeral by design (can be replaced)
CRI

Container Runtime

Software responsible for running containers

The container runtime is responsible for pulling container images, unpacking the container, and running the application. Kubernetes supports several container runtimes through the Container Runtime Interface (CRI).

Supported Runtimes:
Docker (via dockershim) containerd CRI-O Kata Containers
KBL

Kubelet

Primary node agent running on each node

Kubelet is the primary "node agent" that runs on each node. It works in terms of a PodSpec (a YAML or JSON object that describes a pod) and ensures containers described in PodSpecs are running and healthy.

Kubelet Responsibilities:
  • • Registers node with API server
  • • Monitors pod specifications from API server
  • • Ensures containers are running and healthy
  • • Reports node and pod status back to API server
  • • Mounts volumes and manages secrets
PRX

Kube-Proxy

Network proxy running on each node

Kube-proxy is a network proxy that runs on each node. It maintains network rules on nodes that allow network communication to Pods from network sessions inside or outside the cluster.

Key Functions:
  • • Implements Kubernetes Service concept
  • • Maintains network rules (iptables/IPVS)
  • • Performs connection forwarding
  • • Enables Service IP-based load balancing

Kubernetes Extensions

Kubernetes can be extended with additional components that enhance its functionality, providing better observability, management, and user experience.

Web Admin UI (Dashboard)

Web-based management interface

General-purpose web UI for Kubernetes clusters that allows users to manage applications running in the cluster and troubleshoot them, as well as manage the cluster itself.

DNS (CoreDNS)

Cluster DNS server

Provides service discovery within the cluster. Kubernetes DNS schedules a DNS Pod and Service on the cluster and configures kubelets to use the DNS Service's IP to resolve DNS names.

CLI (kubectl)

Command-line interface

Command-line tool for communicating with the Kubernetes API server. kubectl is used for deploying applications, inspecting and managing cluster resources, and viewing logs.

Container Resource Monitoring

Metrics and monitoring

Provides monitoring capabilities for cluster resources. Tools like Metrics Server, Prometheus, and Grafana collect and visualize container metrics, performance data, and cluster health.

Essential kubectl Commands

kubectl is the primary CLI tool for interacting with Kubernetes clusters. Here are the most commonly used commands for managing your Kubernetes resources.

Cluster Information

Display cluster information 

$ kubectl cluster-info

Get cluster nodes

$ kubectl get nodes

Get kubectl version

$ kubectl version

Pod Management

List all pods in current namespace

$ kubectl get pods

List all pods in all namespaces

$ kubectl get pods --all-namespaces

Get detailed information about a pod

$ kubectl describe pod <pod-name>

Delete a pod

$ kubectl delete pod <pod-name>

Get pod logs

$ kubectl logs <pod-name>

Execute command in a pod 

$ kubectl exec -it <pod-name> -- /bin/bash

Deployment Management

List deployments

$ kubectl get deployments

Create deployment

$ kubectl create deployment <name> --image=<image>

Scale deployment

$ kubectl scale deployment <name> --replicas=3

Update deployment image

$ kubectl set image deployment/<name> <container>=<new-image>

Rollback deployment

$ kubectl rollout undo deployment/<name>

Check rollout status

$ kubectl rollout status deployment/<name>

Service Management

List services

$ kubectl get services

Expose deployment as service 

$ kubectl expose deployment <name> --port=80 --type=LoadBalancer

Delete service

$ kubectl delete service <service-name>

Configuration & Resources

Apply configuration from file

$ kubectl apply -f <file.yaml>

Delete resources from file 

$ kubectl delete -f <file.yaml>

Get all resources

$ kubectl get all

View resource YAML

$ kubectl get <resource> <name> -o yaml

Namespace Management

List namespaces

$ kubectl get namespaces

Create namespace

$ kubectl create namespace <name>

Set default namespace

$ kubectl config set-context --current --namespace=<name>

Kubernetes Resource Types

Kubernetes uses various resource types to manage applications and infrastructure. Understanding these resources is essential for effective cluster management.

Deployment

Manages replicated applications and provides declarative updates for Pods and ReplicaSets.

Service

Exposes applications running on a set of Pods as a network service.

ConfigMap

Stores non-confidential configuration data in key-value pairs.

Secret

Stores sensitive information like passwords, OAuth tokens, and SSH keys.

Ingress

Manages external access to services, typically HTTP/HTTPS routing.

PersistentVolume

Storage resource in the cluster that persists beyond pod lifecycle.

Namespace

Provides logical isolation for resources within a cluster.

StatefulSet

Manages stateful applications with stable network identities and persistent storage.

DaemonSet

Ensures all (or some) nodes run a copy of a Pod.

Job

Creates one or more Pods and ensures that a specified number complete successfully.

CronJob

Creates Jobs on a repeating schedule.

HorizontalPodAutoscaler

Automatically scales the number of Pods based on observed CPU utilization or custom metrics.

Related Cheatsheets

Expand your knowledge with these related cheatsheets that complement your Kubernetes expertise.

Docker

Container runtime and image management essentials

OPS

DevOps Tools

CI/CD pipelines and automation for K8s deployments

NET

Linux Networking

Network configuration for Kubernetes clusters
CLI

Linux Commands

Essential commands for server administration
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