Scale and Load Balance Applications

Introduction

In this lab, you will start a local Kubernetes cluster using Minikube, deploy a sample NGINX application, and then scale it to meet varying demands. You will observe load balancing across multiple pods, monitor cluster events, and gain a brief introduction to Horizontal Pod Autoscaler (HPA) for future scaling automation. This lab aims to provide a comprehensive, hands-on experience for understanding Kubernetes scaling and load balancing.

Skills Graph

Start the Kubernetes Cluster

In this step, you'll learn how to start and verify a local Kubernetes cluster using Minikube. This is an essential first step for deploying and managing containerized applications in a Kubernetes environment.

First, start the Minikube cluster:

minikube start

Example output:

😄  minikube v1.29.0 on Ubuntu 22.04
✨  Automatically selected the docker driver
📌  Using Docker driver with root permissions
🔥  Creating kubernetes in kubernetes cluster
🔄  Restarting existing kubernetes cluster
🐳  Preparing Kubernetes v1.26.1 on Docker 20.10.23 ...
🚀  Launching Kubernetes ...
🌟  Enabling addons: storage-provisioner, default-storageclass
🏄  Done! kubectl is now configured to use "minikube" cluster and "default" namespace

Verify the cluster status using multiple commands:

minikube status
kubectl get nodes

Example output for minikube status:

minikube
type: Control Plane
host: Running
kubelet: Running
apiserver: Running
kubeconfig: Configured

Example output for kubectl get nodes:

NAME       STATUS   ROLES           AGE   VERSION
minikube   Ready    control-plane   1m    v1.26.1

These commands confirm that:

1. Minikube is successfully running.
2. A local Kubernetes cluster has been created.
3. The cluster is ready to use.
4. You have a single-node cluster with control plane capabilities.

Deploy a Sample Application

In this step, you'll learn how to deploy a simple web application using a Kubernetes Deployment with a single replica. We'll create a YAML manifest for an NGINX web server and apply it to the Minikube cluster. Understanding how to deploy an application is fundamental to using Kubernetes.

First, create a directory for your Kubernetes manifests:

mkdir -p ~/project/k8s-manifests
cd ~/project/k8s-manifests

Create a new YAML file for the deployment:

nano nginx-deployment.yaml

Add the following deployment configuration:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  labels:
    app: nginx
spec:
  replicas: 1
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
        - name: nginx
          image: nginx:latest
          ports:
            - containerPort: 80

Save the file (Ctrl+X, then Y, then Enter).

Explanation of the YAML configuration:

• apiVersion: apps/v1: Specifies the API version for Deployments.
• kind: Deployment: Indicates that this is a Deployment object, used to manage replicated applications.
• metadata: Contains metadata about the Deployment.
  • name: nginx-deployment: The name of the deployment.
  • labels: app: nginx: A label used to identify this deployment.
• spec: Contains the deployment specification.
  • replicas: 1: The desired number of pod instances (replicas). In this initial deployment, we have only one replica.
  • selector: Defines how the deployment will select pods to manage.
    • matchLabels: app: nginx: Pods with the label app: nginx will be managed by this deployment.
  • template: The pod template. It specifies the configuration for the pods the deployment creates.
    • metadata.labels: app: nginx: Label that applies to pods managed by this deployment
    • spec.containers: Defines the containers in the pod
      • name: nginx: The name of the container.
      • image: nginx:latest: The Docker image for the container (using the latest NGINX image).
      • ports: containerPort: 80: Exposes port 80 in the container.

Apply the deployment to the Kubernetes cluster:

kubectl apply -f nginx-deployment.yaml

Example output:

deployment.apps/nginx-deployment created

Verify the deployment status:

kubectl get deployments
kubectl get pods

Example output for kubectl get deployments:

NAME               READY   UP-TO-DATE   AVAILABLE   AGE
nginx-deployment   1/1     1            1           30s

Example output for kubectl get pods:

NAME                                READY   STATUS    RESTARTS   AGE
nginx-deployment-xxx-yyy            1/1     Running   0          30s

Key points about this deployment:

1. We created a Deployment with a single replica.
2. The deployment uses the latest NGINX image.
3. The container exposes port 80.
4. The deployment has a label app: nginx for identification.

Inspect the deployment details:

kubectl describe deployment nginx-deployment

Example output will show deployment configuration, events, and current state.

Scale Deployments to Handle Increased Load

In this step, you will learn how to scale your application to handle more traffic. In the real world, as your application becomes more popular, one replica may not be sufficient to handle the load. To address this, Kubernetes allows you to easily scale out your application by increasing the number of pod instances (replicas).

Before scaling, let’s briefly discuss why multiple replicas are necessary. A single replica of an application can only handle a certain amount of concurrent requests. If the traffic increases beyond that capacity, the application can become slow or unresponsive. By having multiple replicas, the load can be distributed across different pod instances, ensuring that the application remains responsive and available. This concept is essential for creating scalable applications.

You will now learn how to scale your Kubernetes deployment by modifying the replicas field in the YAML manifest, and also by using the kubectl scale command.

Open the previously created deployment manifest:

nano ~/project/k8s-manifests/nginx-deployment.yaml

Modify the replicas field from 1 to 3:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  labels:
    app: nginx
spec:
  replicas: 3 ## Changed from 1 to 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
        - name: nginx
          image: nginx:latest
          ports:
            - containerPort: 80

Save the file (Ctrl+X, then Y, then Enter).

Apply the updated deployment:

kubectl apply -f ~/project/k8s-manifests/nginx-deployment.yaml

Example output:

deployment.apps/nginx-deployment configured

Verify the scaled deployment:

kubectl get deployments
kubectl get pods

Example output for kubectl get deployments:

NAME               READY   UP-TO-DATE   AVAILABLE   AGE
nginx-deployment   3/3     3            3           5m

Example output for kubectl get pods:

NAME                                READY   STATUS    RESTARTS   AGE
nginx-deployment-xxx-yyy            1/1     Running   0          5m
nginx-deployment-xxx-zzz            1/1     Running   0          30s
nginx-deployment-xxx-www            1/1     Running   0          30s

Alternative scaling method using kubectl scale:

kubectl scale deployment nginx-deployment --replicas=4

Example output:

deployment.apps/nginx-deployment scaled

Verify the new number of replicas:

kubectl get deployments
kubectl get pods

Key points about scaling:

1. Modify replicas in the YAML file or use the kubectl scale command.
2. Use kubectl apply to update the deployment when making changes to the YAML file.
3. Kubernetes ensures the desired number of replicas are running.
4. You can scale both up (increase replicas) or down (decrease replicas).

Verify Load Balancing by Checking Multiple Pod Responses

In this step, you'll learn how to verify load balancing in Kubernetes by creating a Service and checking responses from multiple pods. Load balancing is crucial for distributing traffic across multiple replicas, ensuring that no single pod is overwhelmed. Kubernetes Services handle this process automatically.

Create a service to expose the deployment:

nano ~/project/k8s-manifests/nginx-service.yaml

Add the following service configuration:

apiVersion: v1
kind: Service
metadata:
  name: nginx-service
spec:
  selector:
    app: nginx
  type: ClusterIP
  ports:
    - port: 80
      targetPort: 80

Save the file (Ctrl+X, then Y, then Enter).

Explanation of the YAML configuration:

• apiVersion: v1: Specifies the API version for Services.
• kind: Service: Indicates that this is a Service object.
• metadata: Contains metadata about the Service.
  • name: nginx-service: The name of the Service.
• spec: Contains the service specification.
  • selector: Defines which pods this service will route traffic to.
    • app: nginx: Selects pods with the label app: nginx, which matches the pods created in the previous step.
  • type: ClusterIP: Creates an internal service with a cluster IP address, used for internal communication. This service type is only reachable within the Kubernetes cluster.
  • ports: Defines how the service will map traffic.
    • port: 80: The port that the service exposes.
    • targetPort: 80: The port that the application inside the container is listening on.

Apply the service:

kubectl apply -f ~/project/k8s-manifests/nginx-service.yaml

Example output:

service/nginx-service created

Verify the service:

kubectl get services

Example output:

NAME            TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)   AGE
kubernetes      ClusterIP   10.96.0.1       <none>        443/TCP   30m
nginx-service   ClusterIP   10.96.xxx.xxx   <none>        80/TCP    30s

Now, to truly verify load balancing, you will create a temporary pod and send multiple requests to the service. This allows you to see that the requests are being distributed across different NGINX pods.

Create a temporary pod to test load balancing:

kubectl run curl-test --image=curlimages/curl --rm -it -- sh

This command does the following:

• kubectl run curl-test: Creates a new pod named curl-test.
• --image=curlimages/curl: Uses a Docker image with curl installed.
• --rm: Automatically removes the pod when it is finished.
• -it: Allocates a pseudo-TTY and keeps stdin open.
• -- sh: Starts a shell session in the pod.

Inside the temporary pod, run multiple requests:

for i in $(seq 1 10); do curl -s nginx-service | grep -q "Welcome to nginx!" && echo "Welcome to nginx - Request $i"; done

This loop will send 10 requests to the nginx-service. Each request should be routed to one of the available NGINX pods. The output will print Welcome to nginx - Request $i for each successful request.

Example output:

Welcome to nginx - Request 1
Welcome to nginx - Request 2
Welcome to nginx - Request 3
...

Exit the temporary pod:

exit

Key points about load balancing:

1. Services distribute traffic across all matching pods.
2. Each request can potentially hit a different pod.
3. Kubernetes uses a round-robin approach by default.
4. The ClusterIP service type provides internal load balancing.
5. The curl test shows the load being distributed across multiple NGINX instances.

Dynamically Adjust the Deployment Scale to Meet Demand

In this step, you will practice dynamically adjusting your Kubernetes deployment scale to meet changing application demands using the kubectl scale command. This step emphasizes the practical aspect of adjusting the number of running replicas without directly modifying the YAML file, which can be useful for rapid adjustments in response to traffic spikes.

First, check the current deployment status:

kubectl get deployments

Example output:

NAME               READY   UP-TO-DATE   AVAILABLE   AGE
nginx-deployment   4/4     4            4           45m

Scale the deployment using the kubectl command:

kubectl scale deployment nginx-deployment --replicas=5

Example output:

deployment.apps/nginx-deployment scaled

Verify the new number of replicas:

kubectl get deployments
kubectl get pods

Example output for deployments:

NAME               READY   UP-TO-DATE   AVAILABLE   AGE
nginx-deployment   5/5     5            5           46m

Example output for pods:

NAME                                READY   STATUS    RESTARTS   AGE
nginx-deployment-xxx-yyy            1/1     Running   0          1m
nginx-deployment-xxx-zzz            1/1     Running   0          1m
nginx-deployment-xxx-www            1/1     Running   0          1m
nginx-deployment-xxx-aaa            1/1     Running   0          1m
nginx-deployment-xxx-bbb            1/1     Running   0          1m

Now, update the deployment YAML for persistent scaling:

nano ~/project/k8s-manifests/nginx-deployment.yaml

Modify the replicas field:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  labels:
    app: nginx
spec:
  replicas: 5 ## Updated from previous value
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
        - name: nginx
          image: nginx:latest
          ports:
            - containerPort: 80

Apply the updated configuration:

kubectl apply -f ~/project/k8s-manifests/nginx-deployment.yaml

Example output:

deployment.apps/nginx-deployment configured

Simulate scaling down for reduced demand:

kubectl scale deployment nginx-deployment --replicas=2

Example output:

deployment.apps/nginx-deployment scaled

Verify the reduced number of replicas:

kubectl get deployments
kubectl get pods

Key points about scaling:

1. Use kubectl scale for quick, temporary scaling.
2. Update YAML for persistent configuration.
3. Kubernetes ensures smooth scaling with minimal disruption.
4. You can scale up or down based on application needs using both command and configuration.

Monitor Deployment and Pod Events for Changes

In this step, you'll learn how to monitor Kubernetes deployments and pods using various kubectl commands to track changes, troubleshoot issues, and understand the lifecycle of your applications. Observability is crucial for ensuring the health and performance of your applications.

Describe the current deployment to get detailed information:

kubectl describe deployment nginx-deployment

Example output:

Name:                   nginx-deployment
Namespace:              default
CreationTimestamp:      [timestamp]
Labels:                 app=nginx
Replicas:               2 desired | 2 updated | 2 total | 2 available | 0 unavailable
StrategyType:           RollingUpdate
MinReadySeconds:        0
RollingUpdateStrategy:  25% max unavailable, 25% max surge
Pod Template:
  Labels:  app=nginx
  Containers:
   nginx:
    Image:        nginx:latest
    Port:         80/TCP
    Host Port:    0/TCP
    Environment:  <none>
    Mounts:       <none>
Conditions:
  Type           Status  Reason
  ----           ------  ------
  Available      True    MinimumReplicasAvailable
  Progressing    True    NewReplicaSetAvailable
OldReplicaSets:  <none>
NewReplicaSet:   nginx-deployment-xxx (2/2 replicas created)
Events:          <some deployment events>

Get detailed information about individual pods:

kubectl describe pods -l app=nginx

Example output will show details for each pod, including:

• Current status
• Container information
• Events
• IP addresses
• Node information

View cluster-wide events:

kubectl get events

Example output:

LAST SEEN   TYPE      REASON              OBJECT                           MESSAGE
5m          Normal    Scheduled           pod/nginx-deployment-xxx-yyy    Successfully assigned default/nginx-deployment-xxx-yyy to minikube
5m          Normal    Pulled              pod/nginx-deployment-xxx-yyy    Container image "nginx:latest" already present on machine
5m          Normal    Created             pod/nginx-deployment-xxx-yyy    Created container nginx
5m          Normal    Started             pod/nginx-deployment-xxx-yyy    Started container nginx

Filter events for specific resources:

kubectl get events --field-selector involvedObject.kind=Deployment

Example output will show only deployment-related events.

Simulate an event by deleting a pod:

## Get a pod name
POD_NAME=$(kubectl get pods -l app=nginx -o jsonpath='{.items[0].metadata.name}')

## Delete the pod
kubectl delete pod $POD_NAME

Observe the events and pod recreation:

kubectl get events
kubectl get pods

Key points about monitoring:

1. kubectl describe provides detailed resource information.
2. kubectl get events shows cluster-wide events.
3. Kubernetes automatically replaces deleted pods.
4. Events help troubleshoot deployment issues.
5. Use describe for detailed object information and events to track actions.

Briefly Introduce Horizontal Pod Autoscaler (HPA) for Future Learning

In this step, you'll get an introduction to Horizontal Pod Autoscaler (HPA), a powerful Kubernetes feature that automatically scales applications based on resource utilization. HPA allows you to define scaling rules based on metrics like CPU utilization, memory usage, or even custom metrics.

Understanding HPA:

HPA automatically adjusts the number of running pod replicas in a Deployment, ReplicaSet, or StatefulSet based on observed CPU or memory usage, or based on custom metrics provided by your applications. This ensures that your application can automatically scale to handle changing traffic loads, improving performance and availability.

Enable metrics server addon in Minikube:

minikube addons enable metrics-server

Example output:

* The 'metrics-server' addon is enabled

The metrics server provides Kubernetes with usage data about your resources and it is essential for the HPA to function.

Create a deployment with resource requests:

nano ~/project/k8s-manifests/hpa-example.yaml

Add the following content:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: php-apache
spec:
  selector:
    matchLabels:
      run: php-apache
  replicas: 1
  template:
    metadata:
      labels:
        run: php-apache
    spec:
      containers:
        - name: php-apache
          image: k8s.gcr.io/hpa-example
          ports:
            - containerPort: 80
          resources:
            limits:
              cpu: 500m
            requests:
              cpu: 200m
---
apiVersion: v1
kind: Service
metadata:
  name: php-apache
  labels:
    run: php-apache
spec:
  ports:
    - port: 80
  selector:
    run: php-apache

Apply the deployment:

kubectl apply -f ~/project/k8s-manifests/hpa-example.yaml

Explanation of the YAML configuration:

• This YAML file defines a Deployment for a PHP application and the corresponding Service.
• The Deployment configuration is very similar to the NGINX one, with the exception of:
  • name: php-apache: The name of the deployment and pod container.
  • image: k8s.gcr.io/hpa-example: The Docker image for the container.
  • resources: This section specifies the resource requirements for the container.
    • limits.cpu: 500m: The maximum CPU allowed to use by the container.
    • requests.cpu: 200m: The guaranteed CPU amount assigned to the container.
• The service is a standard service configuration, exposing the deployment internally.

Create an HPA configuration:

nano ~/project/k8s-manifests/php-apache-hpa.yaml

Add the following HPA manifest:

apiVersion: autoscaling/v2
kind: HorizontalPodAutoscaler
metadata:
  name: php-apache
spec:
  scaleTargetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: php-apache
  minReplicas: 1
  maxReplicas: 10
  metrics:
    - type: Resource
      resource:
        name: cpu
        target:
          type: Utilization
          averageUtilization: 50

Apply the HPA configuration:

kubectl apply -f ~/project/k8s-manifests/php-apache-hpa.yaml

Explanation of the YAML configuration:

• apiVersion: autoscaling/v2: Specifies the API version for HorizontalPodAutoscaler.
• kind: HorizontalPodAutoscaler: Indicates that this is an HPA object.
• metadata: Contains metadata about the HPA.
  • name: php-apache: The name of the HPA.
• spec: Contains the HPA specification.
  • scaleTargetRef: Defines the target Deployment that will be scaled.
    • apiVersion: apps/v1: The API version of the target resource.
    • kind: Deployment: The target resource type, which is a Deployment.
    • name: php-apache: The name of the target Deployment to scale.
  • minReplicas: 1: The minimum number of replicas to keep running.
  • maxReplicas: 10: The maximum number of replicas to scale to.
  • metrics: Defines how to determine scaling metrics.
    • type: Resource: Scales based on a resource metric.
    • resource.name: cpu: Scales based on CPU usage.
    • resource.target.type: Utilization: Scales based on a percentage of the CPU requested by the pod
    • resource.target.averageUtilization: 50: Scales when average CPU usage across all pods exceeds 50% of the requests.

Verify the HPA configuration:

kubectl get hpa

Example output:

NAME         REFERENCE              TARGETS         MINPODS   MAXPODS   REPLICAS   AGE
php-apache   Deployment/php-apache  0%/50%          1         10        1          30s

Simulate load to trigger scaling (optional):

kubectl run -i --tty load-generator --rm --image=busybox --restart=Never -- /bin/sh -c "while sleep 0.01; do wget -q -O- http://php-apache; done"

DO NOT CLOSE the terminal with the load generator. OPEN ANOTHER TERMINAL and monitor the HPA behavior:

kubectl get hpa

Wait for a few seconds (it may take more than a minute and a half) to see the HPA scale the deployment based on CPU utilization.

kubectl get hpa
NAME         REFERENCE               TARGETS   MINPODS   MAXPODS   REPLICAS   AGE
php-apache   Deployment/php-apache   68%/50%   1         10        2          72s

Press Ctrl+C to stop the load generator.

Key points about HPA:

1. Automatically scales pods based on resource utilization, which improves application resilience.
2. Can scale based on CPU, memory, or custom metrics.
3. Defines min and max replica counts, ensuring balanced and efficient scaling.
4. HPA is a crucial component for maintaining application performance and availability under varying load.

Summary

In this lab, you've gained hands-on experience with scaling and load balancing in Kubernetes. You started by creating a local Kubernetes cluster with Minikube and deploying a basic NGINX web application. You then explored different scaling methods, including modifying deployment YAML files and using kubectl scale to adjust the number of pod replicas. You learned how to verify load balancing using Kubernetes Services and a temporary test pod.

Furthermore, you learned how to monitor deployments and pods through kubectl describe and kubectl get events commands. Finally, you gained a basic understanding of the Horizontal Pod Autoscaler (HPA), including how it can automatically scale your application based on resource utilization, using an example based on a php-apache image. This lab provides a comprehensive introduction to Kubernetes scaling, load balancing, monitoring, and autoscaling techniques, and sets the foundation for managing more complex applications in Kubernetes.