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July 2025 5 min read

A Practical Guide to Knative: Serverless on Kubernetes

Learn how to deploy and manage serverless workloads on Kubernetes using Knative — covering installation, auto-scaling, eventing, and a full NGINX deployment walkthrough.

Kubernetes Knative Serverless Istio DevOps

Knative is a Kubernetes-based platform for building, deploying, and managing modern serverless workloads. This guide provides a structured overview, setup instructions, and real-world examples for understanding and implementing Knative effectively.

1. What is Knative?

Knative is a Kubernetes extension composed of custom controllers and custom resource definitions (CRDs) that enables serverless capabilities on top of Kubernetes. It abstracts infrastructure complexities so developers can focus on code.

Key Features

- Auto-scaling (to zero)
- Event-driven architecture
- Easy deployment of stateless applications
- Pluggable components
- Developer-friendly tooling

2. Core Components of Knative

Knative is made up of two main components:

2.1 Knative Serving

Handles the deployment and running of serverless workloads:

  • Service — top-level resource managing the full lifecycle
  • Route — maps network endpoints to revisions
  • Configuration — maintains desired state
  • Revision — immutable snapshot of code + config

2.2 Knative Eventing

Supports event-driven architecture and the management of event flow between services using:

  • Broker — event ingress point
  • Trigger — filters events to subscribers
  • Subscription — connects channels to services
  • Channel — persistent event buffer

3. Benefits of Knative

  • Faster container-based development
  • Focus on coding instead of infrastructure
  • Easy entry into serverless computing
  • Integration with tools like Django, Rails, Spring

4. Prerequisites

  • Kubernetes cluster (v1.17+)
  • kubectl CLI installed and configured
  • Sufficient cluster resources

Note: This guide focuses on the Knative Serving component.

5. Installing Knative Serving

5.1 Serving Component

kubectl apply -f https://github.com/knative/serving/releases/download/knative-v1.19.0/serving-crds.yaml
kubectl apply -f https://github.com/knative/serving/releases/download/knative-v1.19.0/serving-core.yaml

5.2 Istio for Networking

kubectl apply -l knative.dev/crd-install=true -f https://github.com/knative/net-istio/releases/download/knative-v1.19.0/istio.yaml
kubectl apply -f https://github.com/knative/net-istio/releases/download/knative-v1.19.0/istio.yaml
kubectl apply -f https://github.com/knative/net-istio/releases/download/knative-v1.19.0/net-istio.yaml

5.3 Verify Installation

kubectl get pods -n knative-serving

6. DNS and Domain Configuration

Apply the default domain:

kubectl apply -f https://github.com/knative/serving/releases/download/knative-v1.19.0/serving-default-domain.yaml

Patch for a custom domain:

kubectl patch configmap/config-domain \
  --namespace knative-serving \
  --type merge \
  --patch '{"data":{"custom.com":""}}'

7. Deploying a Knative Service

apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: helloworld-go
  namespace: default
spec:
  template:
    spec:
      containers:
      - image: gcr.io/knative-samples/helloworld-go
        env:
        - name: TARGET
          value: "IT WORKS!!"

8. Using Knative CLI (kn)

Installation

wget https://github.com/knative/client/releases/download/knative-v1.19.0/kn-linux-amd64
chmod +x kn-linux-amd64 && mv kn-linux-amd64 /usr/local/bin/kn
kn version

9. Using kn-func (Function CLI)

Installation

wget https://github.com/knative/func/releases/download/knative-v1.19.0/func_linux_amd64
chmod +x func_linux_amd64 && mv func_linux_amd64 /usr/local/bin/kn-func

Usage

kn func create -l python py1
kn func build
kn func run
kn func invoke
kn func deploy --namespace default -i docker.io/youruser/knfunc:tag

10. Accessing Services without DNS

# Patch ConfigMap
kubectl patch configmap/config-domain \
  --namespace knative-serving \
  --type merge \
  --patch '{"data":{"custom.com":""}}'

# Access the service
curl -H "Host: nginx.default.custom.com" http://<external-ip>:<port>

11. Virtual Service with Istio

apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: entry-route
  namespace: default
spec:
  gateways:
  - knative-ingress-gateway.knative-serving.svc.cluster.local
  hosts:
  - test.domain.com
  http:
  - match:
    - uri:
        prefix: "/"
    rewrite:
      authority: testapi.default.svc.cluster.local
    route:
    - destination:
        host: knative-local-gateway.istio-system.svc.cluster.local
        port:
          number: 80

12. Auto-Scaling & Serverless Behavior

Knative scales down to zero when the service is idle and scales up automatically on traffic. To enforce a concurrency limit:

kn service update <service-name> --concurrency-limit=1

13. Full NGINX Deployment on Knative

Here is a complete step-by-step NGINX deployment on Knative with all necessary Kubernetes manifests.

Step 1 — PersistentVolume (nginx-pv.yaml)

apiVersion: v1
kind: PersistentVolume
metadata:
  name: nginx-pv
spec:
  capacity:
    storage: 1Gi
  accessModes:
    - ReadWriteOnce
  hostPath:
    path: "/mnt/data/nginx"

Step 2 — PersistentVolumeClaim (nginx-pvc.yaml)

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: nginx-pvc
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 1Gi

Step 3 — ConfigMap (nginx-configmap.yaml)

apiVersion: v1
kind: ConfigMap
metadata:
  name: nginx-config
data:
  default.conf: |
    server {
        listen 80;
        location / {
            root /usr/share/nginx/html;
            index index.html index.htm;
        }
    }

Step 4 — Knative Service (nginx-knative-service.yaml)

apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: nginx
  namespace: default
spec:
  template:
    metadata:
      annotations:
        autoscaling.knative.dev/metric: concurrency
        autoscaling.knative.dev/target: "100"
    spec:
      containers:
      - image: nginx:latest
        volumeMounts:
        - name: html
          mountPath: /usr/share/nginx/html
        - name: config
          mountPath: /etc/nginx/conf.d
      volumes:
      - name: html
        persistentVolumeClaim:
          claimName: nginx-pvc
      - name: config
        configMap:
          name: nginx-config

Step 5 — Istio VirtualService (nginx-virtualservice.yaml)

apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: nginx-vs
  namespace: default
spec:
  gateways:
  - knative-ingress-gateway.knative-serving.svc.cluster.local
  hosts:
  - nginx.custom.com
  http:
  - match:
    - uri:
        prefix: "/"
    rewrite:
      authority: nginx.default.svc.cluster.local
    route:
    - destination:
        host: knative-local-gateway.istio-system.svc.cluster.local
        port:
          number: 80

Access the NGINX Service

# Get Istio ingress IP
kubectl get svc istio-ingressgateway -n istio-system

# Curl with Host header
curl -H "Host: nginx.custom.com" http://<ISTIO_INGRESS_IP>:<PORT>

14. Resources