Raspberry Pi Kubernetes Cluster with OpenFaaS for Serverless Functions (Part 4)

Getting Started with OpenFaaS

This is the fourth post in this series. The focus will be on getting OpenFaaS set up on your Raspberry Pi Kubernetes cluster nice and quickly.

Here are some links to previous posts in this series:

OpenFaaS is an open source project that provides a scalable platform to easily deploy event-driven functions and microservices.

It has great support to run on ARM hardware, which makes it an excellent fit for the Raspberry Pi. It’s worth mentioning that it is of course designed to run across a multitude of different platforms other than the Pi.

Getting Started

You’ll work with a couple of different CLI tools that I chose for the speed at which they can get you up and running:

  • faas-cli – the main CLI for OpenFaaS
  • arkade – a golang based CLI tool for quick and easy one liner installs for various apps / software for Kubernetes

There are other options like Helm or standard YAML files for Kubernetes that you could also use. Find more information about these here.

I have a general purpose admin and routing dedicated Pi in my Raspberry Pi stack that I use for doing admin tasks in my cluster. This made for a great bastion host that I could use to run the following commands:

Install arkade

# Important! Before running these scripts, always inspect the remote content first, especially as they're piped into sh with 'sudo'

# MacOS or Linux
curl -SLsf https://dl.get-arkade.dev/ | sudo sh

# Windows using Bash (e.g. WSL or Git Bash)
curl -SLsf https://dl.get-arkade.dev/ | sh

Install faas-cli

# Important! Before running these scripts, always inspect the remote content first, especially as they're piped into sh with 'sudo'

# MacOS
brew install faas-cli

# Using curl
curl -sL https://cli.openfaas.com | sudo sh

Deploying OpenFaaS

Using arkade, deploy OpenFaaS with:

arkade install openfaas

If you followed my previous articles in this series to set your cluster up, then you’ll have a LoadBalancer service type available via MetalLB. However, in my case (with the above command), I did not deploy a LoadBalancer service, as I already use a single Ingress Controller for external traffic coming into my cluster.

The assumption is that you have an Ingress Controller setup for the remainder of the steps. However, you can get by without one, accessing OpenFaaS by the external gateway NodePortservice instead.

The arkade install will output a command to get your password. By default OpenFaaS comes with Basic Authentication. You’ll fetch the admin password you can use to access the system with Basic Auth next.

Grab the generated admin password and login with faas-cli:

PASSWORD=$(kubectl get secret -n openfaas basic-auth -o jsonpath="{.data.basic-auth-password}" | base64 --decode; echo)
echo -n $PASSWORD | faas-cli login --username admin --password-stdin

OpenFaaS Gateway Ingress

OpenFaaS will have deployed with two Gateway services in the openfaas namespace.

  • gateway (ClusterIP)
  • gateway-external (NodePort)

Instead of relying on the NodePort service, I chose to create an Ingress Rule to send traffic from my cluster’s Ingress Controller to OpenFaaS’ ClusterIP service (gateway).

You’ll want SSL so setup a K8s secret to hold your certificate details for the hostname you choose for your Ingress Rule. Here is a template you can use for your OpenFaaS ingress:

apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  annotations:
    kubernetes.io/ingress.class: nginx
    nginx.ingress.kubernetes.io/rewrite-target: /
  name: openfaas
spec:
  rules:
  - host: openfaas.foo.bar
    http:
      paths:
      - backend:
          serviceName: gateway
          servicePort: 8080
        path: /
  tls:
  - hosts:
    - openfaas.foo.bar
    secretName: openfaas.foo.bar

Create your TLS K8s secret in the openfaas namespace, and then deploy the ingress rule with:

kubectl -n openfaas apply -f ./the_above_ingress_rule.yml

You should now be able to access the OpenFaaS UI with something like https://openfaas.foo.bar/ui/

The OpenFaas Web UI

Creating your own Functions

Life is far more fun on the CLI, so get started with some basics with first:

  • faas-cli store list --platform armhf – show some basic functions available for armhf (Pi)
  • faas-cli store deploy figlet --platform armhf – deploy the figlet function that converts text to ASCII representations of that text
  • echo "hai" | faas-cli invoke figlet – pipe the text ‘hai’ into the faas-cli invoke command to invoke the figlet function and get it to generate the equivalent in ASCII text.

Now, create your own function using one of the many templates available. You’ll be using the incubator template for python3 HTTP. This includes a newer function watchdog (more about that below), which gives more control over the HTTP / event lifecycle in your functions.

Grab the python3 HTTP template for armhf and create a new function with it:

# Grab incubator templates for Python, including Python HTTP. Will figure out it needs the armhf ones based on your architecture!

faas template pull https://github.com/openfaas-incubator/python-flask-template
faas-cli new --lang python3-http-armhf your-function-name-here
Success – a new, python3 HTTP function ready to go

A basic file structure gets scaffolded out. It contains a YAML file with configuration about your function. E.g.

version: 1.0
provider:
  name: openfaas
  gateway: http://127.0.0.1:8080
functions:
  your-function-name-here:
    lang: python3-http-armhf
    handler: ./your-function-name-here
    image: your-function-name-here:latest

The YAML informs building and deploying of your function.

A folder with your function handler code is also created alongside the YAML. For python it contains handler.py and requirements.txt (for python library requirements)

def handle(event, context):
    # TODO implement
    return {
        "statusCode": 200,
        "body": "Hello from OpenFaaS!"
    }

As you used the newer function templates with the latest OF Watchdog, you get full access to the event and context in your handler without any extra work. Nice!

Build and Deploy your Custom Function

Run the faas up command to build and publish your function. This will do a docker build / tag / push to a registry of your choice and then deploy the function to OpenFaaS. Update your your-function-name-here.yml file to specify your desired docker registry/repo/tag, and OpenFaas gateway address first though.

faas up -f your-function-name-here.yml

Now you’re good to go. Execute your function by doing a GET request to the function URL, using faas invoke, or by using the OpenFaaS UI!

Creating your own OpenFaaS Docker images

You can convert most Docker images to run on OpenFaaS by adding the function watchdog to your image. This is a very small HTTP server written in Golang.

It becomes the entrypoint which forwards HTTP requests to your target process via STDIN or HTTP. The response goes back to the requester by STDOUT or HTTP.

Read and find out more at these URLs:

Hopefully this gave you a good base to get started with OpenFaaS. We covered everything from deployment and configuration, to creating your own custom functions and images. Have fun experimenting!

Building a Pi Kubernetes Cluster – Part 3 – Worker Nodes and MetalLB

Building a Raspberry Pi Kubernetes Cluster - part 3 - worker nodes featured image

This is the third post in this series and the focus will be on completing the Raspberry Pi Kubernetes cluster by adding a worker node. You’ll also setup a software based load-balancer implementation designed for bare metal Kubernetes Clusters by leveraging MetalLB.

Here are some handy links to other parts in this blog post series:

By now you should have 1 x Pi running as the dedicated Pi network router, DHCP, DNS and jumpbox, as well as 1 x Pi running as the cluster Master Node.

Of course it’s always best to have more than 1 x Master node, but as this is just an experimental/fun setup, one is just fine. The same applies to the Worker nodes, although in my case I added two workers with each Pi 4 having 4GB RAM.

Joining a Worker Node to the Cluster

Start off by completing the setup steps as per the Common Setup section in Part 2 with your new Pi.

Once your new Worker Pi is ready and on the network with it’s own static DHCP lease, join it to the cluster (currently only the Master Node) by using the kubeadm join command you noted down when you first initialised your cluster in Part 2.

E.g.

sudo kubeadm join 10.0.0.50:6443 --token kjx8lp.wfr7n4ie33r7dqx2 \
     --discovery-token-ca-cert-hash sha256:25a997a1b37fb34ed70ff4889ced6b91aefbee6fb18e1a32f8b4c8240db01ec3

After a few moments, SSH back to your master node and run kubectl get nodes. You should see the new worker node added and after it pulls down and starts the weave net CNI image it’s status will change to Ready.

kubernetes worker node added to cluster

Setting up MetalLB

The problem with a ‘bare metal’ Kubernetes cluster (or any self-installed, manually configured k8s cluster for that matter) is that it doesn’t have any load-balancer implementation to handle LoadBalancer service types.

When you run Kubernetes on top of a cloud hosting platform like AWS or Azure, they are backed natively by load-balancer implementations that work seamlessly with those cloud platform’s load-balancer services. E.g. classic application or elastic load balancers with AWS.

However, with a Raspberry Pi cluster, you don’t have anything fancy like that to provide LoadBalancer services for your applications you run.

MetalLB provides a software based implementation that can work on a Pi cluster.

Install version 0.8.3 of MetalLB by applying the following manifest with kubectl:

kubectl apply -f https://gist.githubusercontent.com/Shogan/d418190a950a1d6788f9b168216f6fe1/raw/ca4418c7167a64c77511ba44b2c7736b56bdad48/metallb.yaml

Make sure the MetalLB pods are now up and running in the metallb-system namespace that was created.

metallb pods running

Now you will create a ConfigMap that will contain the settings your MetalLB setup will use for the cluster load-balancer services.

Create a file called metallb-config.yaml with the following content:

apiVersion: v1
kind: ConfigMap
metadata:
  namespace: metallb-system
  name: config
data:
  config: |
    address-pools:
    - name: default
      protocol: layer2
      addresses:
      - 10.23.220.88-10.23.220.98

Update the addresses section to use whichever range of IP addresses you would like to assign for use with MetalLB. Note, I only used 10 addresses as below for mine.

Apply the configuration:

kubectl apply -f ./metallb-config.yaml

Setup Helm in the Pi Cluster

First of all you’ll need an ARM compatible version of Helm. Download it and move it to a directory that is in your system PATH. I’m using my Kubernetes master node as a convenient location to use kubectl and helm commands from, so I did this on my master node.

Install Helm Client

export HELM_VERSION=v2.9.1
wget https://kubernetes-helm.storage.googleapis.com/helm-$HELM_VERSION-linux-arm.tar.gz
tar xvzf helm-$HELM_VERSION-linux-arm.tar.gz
sudo mv linux-arm/helm /usr/bin/helm

Install Helm Tiller in the Cluster

Use the following command to initialise the tiller component in your Pi cluster.

helm init --tiller-image=jessestuart/tiller --service-account tiller --override spec.selector.matchLabels.'name'='tiller',spec.selector.matchLabels.'app'='helm' --output yaml | sed 's@apiVersion: extensions/v1beta1@apiVersion: apps/v1@' | kubectl apply -f -

Note: it uses a custom image from jessestuart/tiller (as this is ARM compatible). The command also replaces the older api spec for the deployment with the apps/v1 version, as the older beta one is no longer applicable with Kubernetes 1.16.

Deploy an Ingress Controller with Helm

Now that you have something to fulfill LoadBalancer service types (MetalLB), and you have Helm configured, you can deploy an NGINX Ingress Controller with a LoadBalancer service type for your Pi cluster.

helm install --name nginx-ingress stable/nginx-ingress --set rbac.create=true --set controller.service.type=LoadBalancer

If you list out your new ingress controller pods though you might find a problem with them running. They’ll likely be trying to use x86 architecture images instead of ARM. I manually patched my NGINX Ingress Controller deployment to point it at an ARM compatible docker image.

kubectl set image deployment/nginx-ingress-controller     nginx-ingress-controller=quay.io/kubernetes-ingress-controller/nginx-ingress-controller-arm:0.26.1

After a few moments the new pods should now show as running:

new nginx ingress pods running with ARM image

Now to test everything, you can grab the external IP that should have been assigned to your NGINX ingress controller LoadBalancer service and test the default NGINX backend HTTP endpoint that returns a simple 404 message.

List the service and get the EXTERNAL-IP (this should sit in the range you configured MetalLB with):

kubectl get service --selector=app=nginx-ingress

Curl the NGINX Ingress Controller LoadBalancer service endpoint with a simple GET request:

curl -i http://10.23.220.88

You’ll see the default 404 not found response which indicates that the controller did indeed receive your request from the LoadBalancer service and directed it appropriately down to the default backend pod.

the nginx default backend 404 response

Concluding

At this point you’ve configured:

  • A Raspberry Pi Kubernetes network Router / DHCP / DNS server / jumpbox
  • Kubernetes master node running the master components for the cluster
  • Kubernetes worker nodes
  • MetalLB load-balancer implementation for your cluster
  • Helm client and Tiller agent for ARM in your cluster
  • NGINX ingress controller

In part 1, recall you setup some iptables rules on the Router Pi as an optional step?

These PREROUTING AND POSTROUTING rules were to forward packets destined for the Router Pi’s external IP address to be forwarded to a specific IP address in the Kubernetes network. In actual fact, the example I provided was what I used to forward traffic from the Pi router all the way to my NGINX Ingress Controller load balancer service.

Revisit this section if you’d like to achieve something similar (access services inside your cluster from outside the network), and replace the 10.23.220.88 IP address in the example I provided with the IP address of your own ingress controller service backed by MetalLB in your cluster.

Also remember that at this point you can add as many worker nodes to the cluster as you like using the kubeadm join command used earlier.