Understanding Kubernetes: Part 25 Affinity and Anti-Affinity

---

📢 If you’ve been following our Kubernetes series 2025, welcome back! For new readers, check out Part 24: Taints and Tolerations

What is Node Affinity?

Node Affinity is a rule that ensures Pods are scheduled on specific nodes based on defined labels.

What is Pod Affinity and Anti-Affinity?

• Pod Affinity ensures that Pods are scheduled close to other Pods based on label selectors.

• Pod Anti-Affinity prevents Pods from being scheduled on the same nodes or within a failure domain.

---

Use Cases

Affinity and Anti-Affinity are useful in various scenarios:

1. Node Affinity

• Ensuring that workloads requiring SSD storage run on nodes labeled with storage=ssd.

• Running GPU-intensive workloads on nodes labeled gpu=true.

2. Pod Affinity

• Ensuring that microservices communicate efficiently by scheduling them on the same node.

• Keeping interdependent applications (e.g., frontend and backend) close together to reduce latency.

3. Pod Anti-Affinity

• Distributing replicas of an application across multiple nodes for high availability.

• Ensuring that critical workloads are not placed on the same node to prevent single points of failure.

---

Node Affinity Syntax

Node Affinity rules are defined in the Pod specification under affinity.nodeAffinity.

Example: Scheduling a Pod on SSD Nodes

apiVersion: v1
kind: Pod
metadata:
  name: ssd-pod
spec:
  affinity:
    nodeAffinity:
      requiredDuringSchedulingIgnoredDuringExecution:
        nodeSelectorTerms:
          - matchExpressions:
              - key: "storage"
                operator: "In"
                values:
                  - "ssd"
  containers:
    - name: app
      image: my-app

This ensures that the Pod is scheduled only on nodes labeled storage=ssd.

---

Pod Affinity Syntax

Pod Affinity rules are defined under affinity.podAffinity.

Example: Placing Pods Close Together

apiVersion: v1
kind: Pod
metadata:
  name: web-pod
spec:
  affinity:
    podAffinity:
      requiredDuringSchedulingIgnoredDuringExecution:
        labelSelector:
          matchLabels:
            app: frontend
        topologyKey: "kubernetes.io/hostname"
  containers:
    - name: web
      image: nginx

This ensures that the Pod is scheduled on the same node as other Pods labeled app=frontend.

---

Pod Anti-Affinity Syntax

Pod Anti-Affinity is defined under affinity.podAntiAffinity.

Example: Spreading Replicas Across Nodes

apiVersion: v1
kind: Pod
metadata:
  name: backend-pod
spec:
  affinity:
    podAntiAffinity:
      requiredDuringSchedulingIgnoredDuringExecution:
        labelSelector:
          matchLabels:
            app: backend
        topologyKey: "kubernetes.io/hostname"
  containers:
    - name: backend
      image: my-backend

This ensures that backend Pods are scheduled on different nodes to improve reliability.

---

In My Previous Role

As a Senior DevOps Engineer, I leveraged Affinity and Anti-Affinity for:

• Optimizing Microservice Deployments: Ensured interdependent services were scheduled on the same node to reduce latency.

• High Availability Strategies: Used Anti-Affinity to distribute replicas across nodes to prevent single points of failure.

• Performance Tuning: Enforced Node Affinity rules to assign workloads to high-memory nodes for better performance.

🚀 Ready to Master Kubernetes?

Take your Kubernetes journey to the next level with the Master Kubernetes: Zero to Hero course! 🌟 Whether you’re a beginner or aiming to sharpen your skills, this hands-on course covers:

✅ Kubernetes Basics — Grasp essential concepts like nodes, pods, and services. ✅ Advanced Scaling — Learn HPA, VPA, and resource optimization. ✅ Monitoring Tools — Master Prometheus, Grafana, and AlertManager. ✅ Real-World Scenarios — Build production-ready Kubernetes setups.

🎓 What You’ll Achieve

💡 Confidently deploy and manage Kubernetes clusters. 🛡️ Secure applications with ConfigMaps and Secrets. 📈 Optimize and monitor resources for peak performance.

🔥 Start Learning Now: [Join the Master Kubernetes Course](https://cloudops0.gumroad.com/l/k8s)

Don’t miss your chance to become a Kubernetes expert! 💻✨

🚀 Stay ahead in DevOps and SRE! 🔔 Subscribe now and never miss a beat on Kubernetes and more. 🌟

🚀 Master Terraform: Infrastructure as Code

🔥 Start Learning Now: Join the Master Terraform Course