Monday, 17 March 2025

Explain architecture of Kubernetes?

Kubernetes has revolutionized the way organizations deploy, scale, and manage containerized applications. Its architecture is a marvel of distributed systems design, combining modularity, scalability, and resilience. This guide provides an exhaustive exploration of Kubernetes architecture, dissecting every component, interaction, and best practice to equip you with the knowledge needed to master production-grade deployments.

Table of Contents

  1. Introduction to Kubernetes Architecture

    • Why Architecture Matters
    • The Evolution of Container Orchestration

  2. Kubernetes Cluster: A Holistic View

    • Control Plane vs. Data Plane
    • Cluster Communication Flow

  3. Control Plane Components: The Brain of Kubernetes

    • kube-apiserver: The Gatekeeper
    • etcd: The Source of Truth
    • kube-scheduler: The Resource Maestro
    • kube-controller-manager: The State Enforcer
    • cloud-controller-manager: The Cloud Integrator

  4. Node Components: The Workhorses

    • kubelet: The Node Agent
    • kube-proxy: The Network Traffic Cop
    • Container Runtime: The Engine of Containers
    • CRI and CSI: Extending Kubernetes’ Capabilities

  5. Add-Ons: Extending Kubernetes’ Functionality

    • Core Add-Ons: DNS, Dashboard, and Metrics Server
    • Networking Plugins: Calico, Cilium, and Flannel
    • Service Meshes: Istio and Linkerd

  6. Component Interactions: How Kubernetes Works Under the Hood

    • API Request Lifecycle
    • Pod Scheduling Workflow
    • Network Traffic Flow

  7. High Availability (HA): Building a Resilient Cluster

    • Multi-Master Control Plane
    • etcd Clustering and Disaster Recovery
    • Node Auto-Scaling and Self-Healing

  8. Security: Locking Down Your Cluster

    • Authentication and Authorization (RBAC)
    • Network Policies and Pod Security
    • Secrets Management and Encryption

  9. Advanced Topics

    • Custom Resource Definitions (CRDs)
    • Operators: Kubernetes-Native Applications
    • Kubernetes Federation: Multi-Cluster Management

  10. Common Pitfalls and Battle-Tested Best Practices

    • Resource Management and Quotas
    • Storage Pitfalls and Solutions
    • Monitoring and Troubleshooting

1. Introduction to Kubernetes Architecture

Why Architecture Matters

Kubernetes isn’t just a tool—it’s a distributed system that manages thousands of containers across hundreds of nodes. Understanding its architecture is critical for:

  • Troubleshooting: Diagnosing why a Pod isn’t scheduled or a Service isn’t reachable.
  • Optimization: Tuning performance for specific workloads (e.g., AI/ML, databases).
  • Security: Identifying attack vectors like unsecured API endpoints or overly permissive RBAC policies.

The Evolution of Container Orchestration

Before Kubernetes, organizations struggled with manual scaling, inconsistent environments, and fragmented tooling. Kubernetes introduced:

  • Declarative Configuration: Define the desired state, and Kubernetes makes it happen.
  • Self-Healing: Automatically replaces failed containers or nodes.
  • Portability: Run the same cluster on-premises, in the cloud, or at the edge.

2. Kubernetes Cluster: A Holistic View

A Kubernetes cluster is a federation of nodes (machines) that together run containerized applications. It’s divided into two planes:

  1. Control Plane: Manages the cluster’s state (e.g., API server, scheduler).
  2. Data Plane: Runs application workloads (e.g., Pods, Deployments).

Cluster Communication Flow

  1. User/Application → kube-apiserver: Requests to create/update/delete resources.
  2. kube-apiserver → etcd: Persists cluster state.
  3. kube-scheduler → Nodes: Assigns Pods to nodes based on policies.
  4. kubelet → Container Runtime: Starts/stops containers.
  5. kube-proxy → Services: Manages network routing.

Kubernetes Architecture Diagram

3. Control Plane Components: The Brain of Kubernetes

1. kube-apiserver

  • Role: Exposes the Kubernetes API and validates requests.
  • Key Features:
    • Authentication: Verifies user/client identities (e.g., X.509 certificates, OIDC).
    • Authorization: Enforces RBAC policies (e.g., “Can user X create Pods?”).
    • Admission Control: Applies policies like PodSecurity or ResourceQuota.
  • Example API Request:
    kubectl get pods --v=9  # Logs API request/response at level 9

2. etcd

  • Role: Distributed key-value store for cluster state.
  • Key Features:
    • Consistency: Uses the Raft consensus algorithm.
    • HA Setup: Deploy 3 or 5 nodes for fault tolerance.
  • Disaster Recovery:
    # Backup etcd
ETCDCTL_API=3 etcdctl --endpoints=https://127.0.0.1:2379 \
  --cacert=/etc/kubernetes/pki/etcd/ca.crt \
  --cert=/etc/kubernetes/pki/etcd/server.crt \
  --key=/etc/kubernetes/pki/etcd/server.key \
  snapshot save /tmp/etcd-backup.db

3. kube-scheduler

  • Role: Assigns Pods to nodes based on resource availability and constraints.
  • Scheduling Process:
    1. Filtering: Eliminates nodes that don’t meet Pod requirements (e.g., CPU, GPU).
    2. Scoring: Ranks nodes based on policies (e.g., spread Pods across zones).
  • Custom Schedulers:
    apiVersion: v1
kind: Pod
metadata:
  name: my-pod
spec:
  schedulerName: my-custom-scheduler  # Use a custom scheduler

4. kube-controller-manager

  • Role: Runs controllers that reconcile the cluster’s actual state with the desired state.
  • Key Controllers:
    • Deployment Controller: Manages ReplicaSets for rolling updates.
    • Node Controller: Monitors node health (e.g., NodeReady condition).
    • PersistentVolume Controller: Binds PVCs to PVs.

5. cloud-controller-manager

  • Role: Integrates with cloud providers to manage resources like load balancers or storage.
  • Example: Automatically creates an AWS Load Balancer for a Service of type LoadBalancer.

4. Node Components: The Workhorses

1. kubelet

  • Role: Ensures containers are running in Pods.
  • Key Tasks:
    • Syncs Pod specs from the API server.
    • Reports node status (e.g., kubectl describe node <node-name>).
  • Config File:
    # /var/lib/kubelet/config.yaml
apiVersion: kubelet.config.k8s.io/v1beta1
kind: KubeletConfiguration
evictionHard:
  memory.available: "500Mi"

2. kube-proxy

  • Role: Manages network rules to route traffic to Pods.
  • Modes:
    • iptables: Default, uses Linux kernel iptables.
    • IPVS: Scalable for large clusters (supports round-robin, least connections).
  • Service Example:
    apiVersion: v1
kind: Service
metadata:
  name: my-service
spec:
  selector:
    app: my-app
  ports:
    - protocol: TCP
      port: 80
      targetPort: 9376
  type: ClusterIP

3. Container Runtime

  • Role: Runs containers (e.g., Docker, containerd, CRI-O).
  • CRI (Container Runtime Interface):
    • Abstract layer allowing Kubernetes to support multiple runtimes.
    • containerd Configuration:
      # /etc/containerd/config.toml
version = 2
[plugins."io.containerd.grpc.v1.cri"]
  sandbox_image = "registry.k8s.io/pause:3.9"

4. CSI (Container Storage Interface)

  • Role: Standardizes storage provisioning across cloud providers.
  • Example: Dynamic provisioning of a PersistentVolume on AWS EBS.
    apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: ebs-gp3
provisioner: ebs.csi.aws.com
parameters:
  type: gp3
  iops: "3000"
  throughput: "125"

5. Add-Ons: Extending Kubernetes’ Functionality

1. Core Add-Ons

  • CoreDNS: Cluster DNS server.
    apiVersion: v1
kind: Pod
metadata:
  name: busybox
spec:
  containers:
  - name: busybox
    image: busybox:1.28
    command: ['sh', '-c', 'nslookup kubernetes.default']
  • Metrics Server: Collects resource usage data for kubectl top.

2. Networking Plugins

  • Calico: Implements network policies.
    apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: deny-all
spec:
  podSelector: {}
  policyTypes:
    - Ingress
    - Egress
  • Cilium: Uses eBPF for advanced networking and security.

3. Service Meshes

  • Istio: Manages traffic, security, and observability.
    apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: reviews
spec:
  hosts:
    - reviews
  http:
    - route:
        - destination:
            host: reviews
            subset: v2

6. Component Interactions: How Kubernetes Works Under the Hood

API Request Lifecycle

  1. Authentication: User/client presents credentials (e.g., token, certificate).
  2. Authorization: RBAC checks if the user has permission.
  3. Admission Control: Mutating/validating webhooks modify/validate the request.
  4. Persistence: etcd stores the new state.
  5. Reconciliation: Controllers adjust resources to match the desired state.

Pod Scheduling Workflow

  1. Pod Creation: User submits a Pod manifest.
  2. Scheduling: kube-scheduler assigns the Pod to a node.
  3. Binding: kube-apiserver updates the Pod’s nodeName field.
  4. Execution: kubelet on the node starts the container.

Network Traffic Flow

  1. Service to Pod: kube-proxy routes traffic via iptables/IPVS rules.
  2. Pod-to-Pod: Uses the CNI plugin (e.g., Calico’s overlay network).

7. High Availability (HA): Building a Resilient Cluster

Multi-Master Control Plane

  • kube-apiserver Load Balancing: Use a cloud load balancer or HAProxy.
  • etcd Clustering:
    # etcd cluster bootstrap
etcd --name etcd-1 --initial-cluster-token my-cluster \
  --initial-cluster etcd-1=http://10.0.0.1:2380,etcd-2=http://10.0.0.2:2380 \
  --initial-advertise-peer-urls http://10.0.0.1: 2380 --listen-peer-urls http://0.0.0.0:2380 \
  --advertise-client-urls http://10.0.0.1:2379 --listen-client-urls http://0.0.0.0:2379

Node Auto-Scaling and Self-Healing

  • Cluster Autoscaler: Automatically adjusts the number of nodes in a cluster based on resource demands.
  • Self-Healing: Kubernetes automatically replaces failed Pods and reschedules them on healthy nodes.

8. Security: Locking Down Your Cluster

Authentication and Authorization (RBAC)

  • RBAC Policies: Define roles and permissions for users and service accounts.
    apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  namespace: default
  name: pod-reader
rules:
  - apiGroups: [""]
    resources: ["pods"]
    verbs: ["get", "list", "watch"]

Network Policies and Pod Security

  • Network Policies: Control traffic flow between Pods.
    apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-specific
spec:
  podSelector:
    matchLabels:
      role: frontend
  ingress:
    - from:
        - podSelector:
            matchLabels:
              role: backend

Secrets Management and Encryption

  • Kubernetes Secrets: Store sensitive information securely.

    apiVersion: v1
kind: Secret
metadata:
  name: my-secret
type: Opaque
data:
  password: cGFzc3dvcmQ=  # base64 encoded

  • Encryption at Rest: Protect sensitive data stored in etcd.

    apiVersion: apiserver.config.k8s.io/v1
kind: EncryptionConfiguration
resources:
  - resources:
      - secrets
    providers:
      - aescbc:
          keys:
            - name: key1
              secret: <base64-encoded-secret>

9. Advanced Topics

Custom Resource Definitions (CRDs)

  • Extending Kubernetes: Create custom resources to manage application-specific configurations.
    apiVersion: apiextensions.k8s.io/v1
kind: CustomResourceDefinition
metadata:
  name: myresources.mygroup.example.com
spec:
  group: mygroup.example.com
  names:
    kind: MyResource
    listKind: MyResourceList
    plural: myresources
    singular: myresource
  scope: Namespaced
  versions:
    - name: v1
      served: true
      storage: true

Operators: Kubernetes-Native Applications

  • Operators: Automate the management of complex applications.
  • Example: A database operator that manages backups, scaling, and upgrades.

Kubernetes Federation: Multi-Cluster Management

  • Federation: Manage multiple Kubernetes clusters as a single entity.
  • Use Cases: Disaster recovery, multi-cloud deployments, and global applications.

10. Common Pitfalls and Battle-Tested Best Practices

Resource Management and Quotas

  • Resource Quotas: Prevent resource hogging by setting limits on CPU and memory usage.
    apiVersion: v1
kind: ResourceQuota
metadata:
  name: my-quota
spec:
  hard:
    requests.cpu: "10"
    requests.memory: "20Gi"
    limits.cpu: "20"
    limits.memory: "40Gi"

Storage Pitfalls and Solutions

  • Persistent Volume Reclaim Policies: Misconfiguring can lead to data loss.
    • Retain: Keeps PV after PVC deletion.
    • Delete: Automatically deletes PV (risky for production).

Monitoring and Troubleshooting

  • Prometheus and Grafana: Monitor cluster health and performance.
  • kubectl Debug: Use for troubleshooting Pods.
    kubectl debug pod/my-pod -it --image=busybox -- sh

Understanding Kubernetes architecture is essential for effectively deploying and managing containerized applications. This guide has provided a comprehensive overview of the components, their interactions, and best practices for building a robust Kubernetes environment.

Next Steps:

  • Hands-On Practice: Set up a local Kubernetes cluster using Minikube or Kind.
  • Explore Advanced Topics: Dive deeper into CRDs, Operators, and Service Meshes.
  • Contribute to the Community: Engage with Kubernetes forums, contribute to open-source projects, or write your own blog posts to share knowledge.
  • Stay Updated: Follow Kubernetes release notes and community updates to keep abreast of new features and best practices.

By mastering Kubernetes architecture, you position yourself to leverage the full power of container orchestration, enabling your organization to innovate faster and more efficiently.

Labels:

posted by Kaavannan K @ March 17, 2025 0 comments

0 Comments:

Post a Comment

Note: only a member of this blog may post a comment.

<< Home