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Kartik Dudeja
Kartik Dudeja

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Going Serverless on Kubernetes with OpenFaaS

#kubernetes #serverless #openfaas #functionasaservice

Build, ship, and scale functions — on your own Kubernetes cluster.

openfaas-k8s

1. What is Serverless?

Serverless allows developers to write and deploy code without worrying about the underlying infrastructure. The server still exists — you just don’t manage it.

Instead of provisioning and scaling servers, you:

  • Write a function
  • Deploy it
  • Let the platform handle the rest (scaling, routing, etc.)

Serverless is about developer experience, efficiency, and auto-scaling — perfect for microservices, APIs, and background tasks.

2. What is OpenFaaS?

OpenFaaS (Functions-as-a-Service) is an open-source serverless framework built for Kubernetes and Docker.

Key Features:

  • Deploy serverless functions in containers
  • CLI, UI, and REST API support
  • Built-in Prometheus metrics
  • Auto-scaling via function invocation count
  • Supports multiple runtimes (Python, Node.js, Go, Bash, etc.)

Serverless on Kubernetes with OpenFaaS:

OpenFaaS runs as a set of Kubernetes components:

  • Gateway: Exposes functions over HTTP
  • Function Pods: Each function is a container
  • Prometheus: Scrapes function invocation metrics
  • Autoscaler: Adds/removes replicas based on load

3. Installing OpenFaaS on Kubernetes with Arkade

Arkade is a simple Kubernetes marketplace for installing apps.

Prerequisites

  • Kubernetes cluster (e.g., minikube, kind, k3s)
  • kubectl installed
  • arkade installed: 
curl -sLS https://get.arkade.dev | sudo sh
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Install OpenFaaS: 

arkade install openfaas
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It will:

  • Create openfaas and openfaas-fn namespaces
  • Deploy the gateway, faas-netes, UI, and Prometheus

4. Accessing the OpenFaaS UI

Get admin password: 

PASSWORD=$(kubectl get secret -n openfaas basic-auth \
-o jsonpath="{.data.basic-auth}" | base64 --decode)
echo $PASSWORD
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Port-forward the gateway: 

kubectl port-forward -n openfaas svc/gateway 8080:8080
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Visit: http://localhost:8080

Login with:

  • Username: admin
  • Password: from the command above

openfaas-ui

5. Creating a Sample Python Function (python3-http)

We’ll use the python3-http template which supports GET/POST with JSON or plain text input.

Step 1: Install the OpenFaaS CLI 

curl -sSL https://cli.openfaas.com | sudo sh
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Login via CLI:

faas-cli login --username admin --password $PASSWORD
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Pull templates from store supported by openfaas 

faas-cli template store pull python3-http
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Step 2: Create the function 

faas-cli new openfaas-py-fn --lang python3-http
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Edit openfaas-py-fn/handler.py:

def handle(event, context):
    name = event.body.decode('utf-8') or "World"
    return {
        "statusCode": 200,
        "body": f"Hello, {name}",
        "headers": {
            "Content-Type": "text/plain"
        }
    }
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Step 3: Update stack.yaml file 

version: 1.0
provider:
  name: openfaas
  gateway: http://127.0.0.1:8080
functions:
  openfaas-py-fn:
    lang: python3-http
    handler: ./openfaas-py-fn
    image: <DOCKERHUB_USERNAME>/openfaas-py-fn:1.1
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Step 4: Build and Deploy 

faas-cli build -f stack.yaml
faas-cli push -f stack.yaml
faas-cli deploy -f stack.yaml
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openfaas-fn-get-pods

6. Accessing the Function via cURL 

curl -X POST http://localhost:8080/function/openfaas-py-fn -d "Testing"
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Or through the UI → Click "Invoke" beside the function.

7. Configuring Auto-Scaling

OpenFaaS autoscaler monitors Prometheus metrics and scales functions automatically.

To customize:

Add this to stack.yaml:

annotations:
  com.openfaas.scale.min: "1"
  com.openfaas.scale.max: "5"
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Redeploy:

faas-cli deploy -f stack.yaml
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Now, your function can scale up to 5 replicas during high load.

8. Prometheus Metrics and Grafana Dashboard

OpenFaaS installs Prometheus by default.

Access Prometheus: 

kubectl port-forward -n openfaas svc/prometheus 9090:9090
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Visit http://localhost:9090

Sample queries:

  • gateway_function_invocation_total
  • gateway_function_invocation_duration_seconds

Grafana for Function Monitoring

You can install Grafana via Arkade:

arkade install grafana
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Then port-forward it:

kubectl port-forward -n default svc/grafana 3000:3000
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Login (default: admin/admin) and add Prometheus as a data source to create dashboards for OpenFaaS function metrics.

9. Load Testing with hey and Testing Auto-Scaling

hey is a lightweight load-testing tool.

Install hey: 

go install github.com/rakyll/hey@latest
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Test Load: 

hey -z 10s -c 1 -m POST -d "Load Testing" http://127.0.0.1:8080/function/openfaas-py-fn
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Flags:

  • -z 10s: Run for 10 seconds
  • -c 1: 1 concurrent users

openfaas-fn-load-testing

Observe Auto-Scaling

Check current function replicas:

kubectl get deploy -n openfaas-fn openfaas-py-fn
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It should scale up under heavy load.

You can also monitor this behavior live via the OpenFaaS UI or Prometheus.

Final Thoughts

OpenFaaS + Kubernetes brings the best of both worlds:

  • The flexibility and portability of containers
  • The simplicity and scalability of serverless

With a single CLI and a UI, OpenFaaS makes it fun to deploy and manage functions — without giving up observability, control, or performance.

{
    "author"   :  "Kartik Dudeja",
    "email"    :  "kartikdudeja21@gmail.com",
    "linkedin" :  "https://linkedin.com/in/kartik-dudeja",
    "github"   :  "https://github.com/Kartikdudeja"
}
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