Horizontal Pod Autoscaler (HPA) automatically increases or decreases the number of Pods based on CPU or memory utilization. In this project, I configured HPA on a local KIND cluster and verified autoscaling using CPU-based metrics.
1. Namespace
A Namespace logically separates Kubernetes resources, making it easier to organize and manage applications independently.
namespace.yml
kind: Namespace
apiVersion: v1
metadata:
name: apache
2. Deployment
The Deployment manages the desired number of application Pods. I configured CPU requests and limits because HPA uses these values to calculate resource utilization and make scaling decisions.
deployment.yml
apiVersion: apps/v1
kind: Deployment
metadata:
name: apache-deployment
namespace: apache
spec:
replicas: 3
selector:
matchLabels:
app: apache-app
template:
metadata:
labels:
app: apache-app
spec:
containers:
- name: apache
image: httpd:latest
imagePullPolicy: Always
ports:
- containerPort: 80
resources:
requests:
cpu: "100m"
memory: "100Mi"
limits:
cpu: "200m"
memory: "250Mi"
3. Service
A Service provides a stable endpoint for accessing the application and distributes incoming traffic across all available Pods.
service.yml
apiVersion: v1
kind: Service
metadata:
name: apache-sv
namespace: apache
spec:
selector:
app: apache-app
ports:
- protocol: TCP
port: 80
targetPort: 80
type: ClusterIP
4. Metrics Server
Metrics Server collects CPU and memory usage from each Pod and exposes these metrics to Kubernetes. Without Metrics Server, HPA cannot monitor resource utilization.
Verify Metrics Server
@root-IdeaPad-Gaming-3-15IHU6:~/Code/K8s/django_hpa$ kubectl top nodes -n apache
NAME CPU(cores) CPU(%) MEMORY(bytes) MEMORY(%)
demo-kind-cluster-control-plane 126m 1% 612Mi 7%
demo-kind-cluster-worker 29m 0% 487Mi 6%
demo-kind-cluster-worker2 27m 0% 471Mi 6%
demo-kind-cluster-worker3 34m 0% 520Mi 6%
@root-IdeaPad-Gaming-3-15IHU6:~/Code/K8s/django_hpa$ kubectl top pods -n apache
NAME CPU(cores) MEMORY(bytes)
apache-deployment-67856f954c-b4n2x 1m 13Mi
apache-deployment-67856f954c-xkmwb 1m 12Mi
If CPU and memory metrics are displayed, the Metrics Server is working correctly.
5. Horizontal Pod Autoscaler (HPA)
The Horizontal Pod Autoscaler continuously monitors CPU utilization and automatically increases or decreases the number of Pod replicas based on the configured target utilization.
hpa.yml
# Horizontal Pod Autoscaler for Django Todo Application
apiVersion: autoscaling/v2
kind: HorizontalPodAutoscaler
metadata:
name: apache-hpa
namespace: apache
spec:
# Target the Apache deployment
scaleTargetRef:
apiVersion: apps/v1
kind: Deployment
name: apache-deployment
# Scaling limits
minReplicas: 2
maxReplicas: 10
# Metrics to scale on
metrics:
# CPU-based scaling
- type: Resource
resource:
name: cpu
target:
type: Utilization
averageUtilization: 50
# Memory-based scaling
- type: Resource
resource:
name: memory
target:
type: Utilization
averageUtilization: 70
# Scaling behavior configuration
behavior:
# Scale down policies
scaleDown:
stabilizationWindowSeconds: 30
policies:
- type: Percent
value: 50
periodSeconds: 15
- type: Pods
value: 2
periodSeconds: 15
selectPolicy: Min
# Scale up policies
scaleUp:
stabilizationWindowSeconds: 0
policies:
- type: Percent
value: 100
periodSeconds: 15
- type: Pods
value: 4
periodSeconds: 15
selectPolicy: Max
6. Generate Load
Generate continuous HTTP requests to simulate client traffic and trigger autoscaling.
while true; do curl -s http://localhost:8000 > /dev/null; done
7. Monitor Autoscaling
Watch the HPA status in real time.
kubectl get hpa -w
Watch Pods being created or terminated.
kubectl get pods -w
Check CPU utilization of each Pod.
kubectl top pods
HPA Workflow
Client Requests
│
▼
Kubernetes Service
│
▼
Deployment
│
▼
Application Pods
│
▼
Metrics Server
│
▼
Horizontal Pod Autoscaler
│
▼
Scale Pods Up or Scale Pods Down
Key Learnings
- HPA automatically scales Pods based on CPU or Memory utilization.
- Metrics Server is mandatory for CPU-based autoscaling.
- CPU requests must be defined in the Deployment.
kubectl top podshelps monitor real-time resource usage.- HPA improves application scalability without manual intervention.
Conclusion
Horizontal Pod Autoscaler makes Kubernetes applications more resilient by automatically adjusting the number of running Pods according to workload demand. This hands-on implementation on a KIND cluster helped me understand the complete autoscaling workflow—from collecting metrics to dynamically scaling application replicas.
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