DEV Community: Mehdi Yedes

Tracking Stripe Payments with Slack and faasd

Mehdi Yedes — Sat, 04 Apr 2020 14:49:54 +0000

In my last blog post, I have written about how to turn a Raspberry Pi into a serverless platform with the lightweight OpenFaas implementation faasd. If you haven't checked it out already, you can find the link to the post below:
Turn your Raspberry Pi into a serverless platform with faasd

Please note that a Raspberry Pi is not required here.

faasd can be installed without issues on any other machine or cloud instance as well.

This blog post from Alex Ellis describes how to build a faasd serverless appliance on DigitalOcan:

https://blog.alexellis.io/deploy-serverless-faasd-with-cloud-init/

I did that only as a small hobby project. But then, I wanted to use this setup for a real-world use case, and also use the opportunity to try another useful open-source project which is inlets.

Inlets is a cloud native tunnel that allows you to expose private endpoints to the Internet. In this case, it will be used to expose the OpenFaas gateway running on my Raspberry Pi board to receive incoming Stripe Webhook events and dispatch them to the relevant function.

For more details about inlets, check the official docs and resources available at https://docs.inlets.dev/

So in this post, I will describe how I built a local OpenFaas function that serves as a Stripe webhook. This function simply sends a Slack notification for every new charge.succeeded event.

The architecture

Pictured: conceptual architecture with faasd for functions, inlets for the tunnel and stripe to generate webhooks.

Inlets is an open source HTTP tunnel which we can use to get a public IP address to receive webhooks. The inlets client will be running on the Raspberry Pi and connects to the inlets server using a websocket connection to listen for any incoming requests.

In our setup, every Stripe webhook event that is received by the inlets client will be forwarded to the OpenFaaS gateway on the Raspberry Pi, which will in turn trigger the stripe-slack-notifier function to send a new Slack notification.

Preparing the Setup

Obtain an exit node with inlets

First, make sure you have created an inlets exit server following this nice guide by Alex Ellis:
Get HTTPS for your local endpoints with inlets and Caddy

This would allow you to have an exit node with a public domain that can be used for receiving webhook events. In the setup described earlier, the inlets client is running on the Raspberry Pi, so I have chosen the upstream to be http://127.0.0.1:8080, which is the OpenFaaS Gateway URL.

Using the token provided by the inlets server, the command below exposes the OpenFaaS Gateway to the Internet:

$ inlets client --remote wss://${REMOTE_EXIT_NODE} --upstream http://127.0.0.1:8080 --token ${INLETS_TOKEN}

Our function will then be available from the Internet using the https://${REMOTE_EXIT_NODE}/function/stripe-slack-notifier

Add a Stripe Webhook

We need to add a new Stripe webhook using the

Create a Slack App

To receive incoming webhooks we need to create an App in the Slack dashboard.

Create a function to receive webhooks from Stripe

The function stripe-slack-notifier was built using the python3-http template that is available in the OpenFaaS template store.

Creating a new function using faas-cli new

$ faas-cli template store list | grep python3-http
python3-http openfaas-incubator Python 3.6 with Flask and HTTP
$ faas-cli template store pull python3-http

# Make sure to set this to you Docker hub username
$ export DOCKER_REGISTRY_PREFIX=<Docker hub username>

$ faas-cli new stripe-slack-notifier --lang python3-http --prefix ${DOCKER_REGISTRY_PREFIX}
Folder: stripe-slack-notifier created.
  ________  ____
 / _ \ _ _____ _ __|___ |_ _ ___/___ |
| | | | '_ \ / _ \ '_ \| |_ / _` |/ _` \___ \
| |_| | |_) | __/ | | | _| (_| | (_| |___) |
 \ ___/| .__ / \ ___|_| |_|_| \__ ,_|\ __,_|____ /
      |_|

Function created in folder: stripe-slack-notifier
Stack file written: stripe-slack-notifier.yml
$ tree .
.
├── stripe-slack-notifier
│   ├── handler.py
│   └── requirements.txt
└── stripe-slack-notifier.yml

The final source code for the function can be found in the mehyedes/stripe-slack-notifierGithub repository.

The function is written in python. It will verify the received payload using the Stripe API key and the webhook singing secret, and then send a slack notification:

import stripe
from babel import numbers
from slack_webhook import Slack

def fetch_secret(secret_name):
    secret_file = open(f"/var/openfaas/secrets/{secret_name}", 'r')
    return secret_file.read()

def handle(event, context):

    # Make sure to create the secrets below
    webhook_url = fetch_secret("slack-webhook-url")
    stripe.api_key = fetch_secret("stripe-secret-key")
    webhook_secret = fetch_secret("webhook-secret")

    payload = event.body
    received_sig = event.headers.get("Stripe-Signature", None)

    try:
        event = stripe.Webhook.construct_event(
            payload, received_sig, webhook_secret
        )
    except ValueError:
        print("Error while decoding event!")
        return {
            "body": "Bad payload",
            "statusCode": 400
        }
    except stripe.error.SignatureVerificationError:
        print("Invalid signature!")
        return {
            "body": "Bad signature", 
            "statusCode": 400
        }

    # Fail for all other event types  
    if event.type != "charge.succeeded":
        return {
            "body":"Unsupported event type",
            "statusCode": 422
        }

    amount = numbers.format_currency(
      event.data.object.amount / 100,
      event.data.object.currency.upper(), 
      locale='en'
    )

    try:
        slack = Slack(url=webhook_url)
        slack.post(text=f"You have a received a new payment of {amount} :moneybag: :tada:")
    except:
        print("An error occured when trying to send slack message.")
        return {
            "body": "Could not send slack message", 
            "statusCode": 500
        }
    return {
        "body": "Notification was sent successfully to Slack", 
        "statusCode": 200
    }

stripe-slack-notifier/handler.py

OpenFaaS secrets are used to pass the following data to the function:

Stripe API key
Webhook signing secret
Slack Webhook URL

So they need to be created manually with faas-cli before deploying the function:

$ faas-cli secret create slack-webhook-url \
  --from-literal=${SLACK_WEBHOOK_URL} --gateway http://raspberrypi.loc:8080
$ faas-cli secret create stripe-secret-key \
  --from-literal=${STRIPE_API_KEY} --gateway http://raspberrypi.loc:8080
$ faas-cli secret create webhook-secret \
  --from-literal=${WEBHOOK_SIGNING_SECRET} --gateway http://raspberrypi.loc:8080
$ faas-cli secret list --gateway http://raspberrypi.loc:8080  

NAME
slack-webhook-url
stripe-secret-key
webhook-secret

Building & deploying the function

Since the function will be running on Raspberry Pi, we need to build the Docker image for armv7.

Fortunately, this has become easier with the multi platform builds feature by buildx available in docker v19.03.

But since we have already exposed our OpenFaaS gateway using inlets, we can use Github Actions to build and deploy the latest version of our function to the Raspberry Pi with every git push. The workflow file used to automate this can be found here.

Manually, this can be achieved with the following steps:

Generate the Docker build context for the function

$ faas-cli build --shrinkwrap -f stripe-slack-notifier.yml

This step is not needed if using Docker for desktop as this would be done automatically for you. On Linux, we need to register other platforms like armv7 with the kernel using the docker/binfmt image:

$ docker run --privileged --rm docker/binfmt:a7996909642ee92942dcd6cff44b9b95f08dad64

Create a new builder for buildx

$ docker buildx create --name armhf --platform linux/arm/v7 
armhf

$ docker buildx ls 
NAME/NODE DRIVER/ENDPOINT STATUS PLATFORMS
armhf * docker-container                    
  armhf0 unix:///var/run/docker.sock running linux/arm/v7, linux/amd64, linux/arm64, linux/riscv64, linux/ppc64le, linux/s390x, linux/386, linux/arm/v7, linux/arm/v6
default docker                              
  default default running linux/amd64, linux/386

Finally build and push the image for both armv7 and amd64 platforms:

$ DOCKER_BUILD_KIT=1 DOCKER_CLI_EXPERIMENTAL=enabled docker buildx build --platform linux/arm/v7,linux/amd64 -t ${DOCKER_REGISTRY_PREFIX}/stripe-slack-notifier:latest --push .

A new Docker image is now available on the Docker registry for both amd64 and armv7 architectures:

To deploy the function to the Raspberry Pi, we can finally run the command below from our laptop:

$ faas-cli deploy -f stripe-slack-notifier.yml -g https://raspberrypi.loc:8080

Test the function

Check the status of the function with faas-cli describe

$ faas-cli describe stripe-slack-notifier --gateway http://raspberrypi.loc:8080
Name: stripe-slack-notifier
Status: Ready
Replicas: 1
Available replicas: 1
Invocations: 0
Image:               
Function process:    
URL: http://raspberrypi.loc:8080/function/stripe-slack-notifier
Async URL: http://raspberrypi.loc:8080/async-function/stripe-slack-notifier

We can test that it's now by triggering some test events from the Stripe dashboard:

After a few moments, we can see a similar message in Slack:

The function only supports charge.succeeded Stripe events for now, so any other type of event will receive Unsupported event type error from the function, and no Slack messages will be sent.

Conclusion

In this blog post, I have described how we can create a serverless webhook handler for Stripe API events using faasd and inlets.

As we have seen in this post, faasd can be a great alternative to running OpenFaaS without the need for managing a Kubernetes or Docker Swarm cluster. Combined with inlets, they can be used together for running and exposing functions for real-world use cases.

Things that you might want to do next:

Join the OpenFaaS community on slack
Extend the mehyedes/stripe-slack-notifier function to support other webhook event types
Build a faasd serverless appliance on a cloud instance using cloud-init (see deploy-serverless-faasd-with-cloud-init)
Try out the inlets-operator for getting public IP addresses for your local kubernetes cluster

Turn your Raspberry Pi into a serverless platform with faasd

Mehdi Yedes — Sun, 01 Mar 2020 16:29:26 +0000

Function-as-a-Service (FaaS) is a serverless computing method that consists on running applications' logic in stateless, ephemeral containers that are triggered by specific events which may last only for one invocation; AWS Lambda and Google Cloud Run are popular implementations of FaaS.

OpenFaaS is a serverless computing framework has been getting a lot of traction in the Open Source community. It allows you to easily build your own FaaS serverless computing platform on top of Docker Swarm or Kubernetes, while also providing you with the tools necessary for building your functions.

faasd makes it possible to run OpenFaaS without the need for a container orchestration engine by relying on containerd, which makes it ideal for a building a serverless home lab that doesn't require much computing resources; perfect for single board computers like Raspberry Pi.

In this blog post, I am going to describe how you can build your own OpenFaaS serverless platform by installing faasd on a single Raspberry Pi, and how you can build and deploy you first function to OpenFaas.

Installing dependencies

First, ssh into your Raspberry Pi to install a few dependencies:

sudo apt update \
    && sudo apt install -qy git runc bridge-utils

Install containerd

Since the Rapsberry Pi has an armv7 architecture

pi@raspberrypi:~ $ uname -m
armv7l

we cannot use the binaries released by the containerd maintainers as they are only compatible with the x86_64.

So in order to install containerd, we can either:

build the binaries on the Raspberry Pi by following the instructions available here OR
use the pre-built binaries that @alexellisuk was kind enough to provide in his Github repo

Let's start by downloading the containerd binaries

pi@raspberrypi:~ $ curl -sSL https://github.com/alexellis/containerd-armhf/releases/download/v1.3.2/containerd.tgz | sudo tar -xvz --strip-components=2 -C /usr/local/bin/
./bin/containerd-shim-runc-v1
./bin/containerd-stress
./bin/ctr
./bin/containerd
./bin/containerd-shim-runc-v2
./bin/containerd-shim

Get the containerd systemd unit file

pi@raspberrypi:~ $ sudo wget --output-document=/etc/systemd/system/containerd.service https://raw.githubusercontent.com/containerd/containerd/v1.3.2/containerd.service--2020-02-09 16:44:04-- https://raw.githubusercontent.com/containerd/containerd/v1.3.2/containerd.service

2020-02-09 16:44:04 (6.45 MB/s) - ‘/etc/systemd/system/containerd.service’ saved [641/641]

Start containerd and enable it at system startup

pi@raspberrypi:~ $ sudo systemctl enable containerd
Created symlink /etc/systemd/system/multi-user.target.wants/containerd.service → /etc/systemd/system/containerd.service.
pi@raspberrypi:~ $ sudo systemctl start containerd.service
pi@raspberrypi:~ $ systemctl status containerd.service 
● containerd.service - containerd container runtime
   Loaded: loaded (/etc/systemd/system/containerd.service; enabled; vendor preset: enabled)
   Active: active (running) since Sun 2020-02-09 16:45:32 CET; 47s ago
     Docs: https://containerd.io
  Process: 2763 ExecStartPre=/sbin/modprobe overlay (code=exited, status=0/SUCCESS)
 Main PID: 2764 (containerd)
    Tasks: 13
   Memory: 19.2M
   CGroup: /system.slice/containerd.service
           └─2764 /usr/local/bin/containerd

Setup container networking

We need to enable the Linux kernel bridge modules and IPv4 forwarding as follows:

pi@raspberrypi:~ $ sudo modprobe br_netfilter
pi@raspberrypi:~ $ sudo sysctl net.bridge.bridge-nf-call-iptables=1
net.bridge.bridge-nf-call-iptables = 1
pi@raspberrypi:~ $ sudo /sbin/sysctl -w net.ipv4.conf.all.forwarding=1

We also need to install the CNI networking plugins using the commands below:

pi@raspberrypi:~ $ sudo mkdir -p /opt/cni/bin
pi@raspberrypi:~ $ curl -sSL https://github.com/containernetworking/plugins/releases/download/v0.8.5/cni-plugins-linux-arm-v0.8.5.tgz | sudo tar -xz -C /opt/cni/bin
pi@raspberrypi:~ $ ls -l /opt/cni/bin/
total 64436
-rwxr-xr-x 1 root root 3775719 Jan 22 19:52 bandwidth
-rwxr-xr-x 1 root root 4255875 Jan 22 19:52 bridge
-rwxr-xr-x 1 root root 10706922 Jan 22 19:52 dhcp
-rwxr-xr-x 1 root root 5394554 Jan 22 19:52 firewall
-rwxr-xr-x 1 root root 2872015 Jan 22 19:52 flannel
-rwxr-xr-x 1 root root 3843695 Jan 22 19:52 host-device
-rwxr-xr-x 1 root root 3359276 Jan 22 19:52 host-local
-rwxr-xr-x 1 root root 3976434 Jan 22 19:52 ipvlan
-rwxr-xr-x 1 root root 3015277 Jan 22 19:52 loopback
-rwxr-xr-x 1 root root 4046458 Jan 22 19:52 macvlan
-rwxr-xr-x 1 root root 3637166 Jan 22 19:52 portmap
-rwxr-xr-x 1 root root 4187702 Jan 22 19:52 ptp
-rwxr-xr-x 1 root root 3152425 Jan 22 19:52 sbr
-rwxr-xr-x 1 root root 2665626 Jan 22 19:52 static
-rwxr-xr-x 1 root root 3087310 Jan 22 19:52 tuning
-rwxr-xr-x 1 root root 3976306 Jan 22 19:52 vlan

Install faasd

Install `faas-cli`

Before installing faasd, let's install faas-cli. faas-cli is the command line utility that can be used to interact with OpenFaaS and allows us to build and deploy functions.

pi@raspberrypi:~ $ curl -sLfS https://cli.openfaas.com | sudo sh
armv7l
Downloading package https://github.com/openfaas/faas-cli/releases/download/0.11.7/faas-cli-armhf as /tmp/faas-cli-armhf
Download complete.

Running with sufficient permissions to attempt to move faas-cli to /usr/local/bin
New version of faas-cli installed to /usr/local/bin
Creating alias 'faas' for 'faas-cli'.
  ________  ____
 / _ \ _ _____ _ __|___ |_ _ ___/___ |
| | | | '_ \ / _ \ '_ \| |_ / _` |/ _` \___ \
| |_| | |_) | __/ | | | _| (_| | (_| |___) |
 \ ___/| .__ / \ ___|_| |_|_| \__ ,_|\ __,_|____ /
      |_|

CLI:
 commit: 30b7cec9634c708679cf5b4d2884cf597b431401
 version: 0.11.7

You can also enable bash-completion for faas-cli using the command below:

pi@raspberrypi:~ $ source <(faas-cli completion --shell bash)

Install `faasd`

Let's fetch the latest faasd binary using the following command

pi@raspberrypi:~ $ sudo wget --output-document=/usr/local/bin/faasd https://github.com/openfaas/faasd/releases/download/0.7.4/faasd-armhf && sudo chmod +x /usr/local/bin/faasd

2020-02-09 17:10:19 (662 KB/s) - ‘/usr/local/bin/faasd’ saved [14548992/14548992]

pi@raspberrypi:~ $ faasd version 
  __ _ 
 / _| _____ _ _____ | |
| |_ / _` |/ _` / __|/ _` |
| _| (_| | (_| \__ \ (_| |
|_| \ __,_|\__ ,_| ___/\__ ,_|

faasd
Commit: 592f3d3cc073ca6af83fac3013cc2f4743d05e52
Version: 0.7.4

Now we just need to run the faasd installation:

pi@raspberrypi:~ $ export GOPATH=$HOME/go/
pi@raspberrypi:~ $ mkdir -p $GOPATH/src/github.com/openfaas
pi@raspberrypi:~ $ cd $GOPATH/src/github.com/openfaas 
pi@raspberrypi:~/go/src/github.com/openfaas $ git clone https://github.com/openfaas/faasd.git
pi@raspberrypi:~/go/src/github.com/openfaas $ cd faasd/
pi@raspberrypi:~/go/src/github.com/openfaas/faasd $ sudo faasd install 
Login with:
  sudo cat /var/lib/faasd/secrets/basic-auth-password | faas-cli login -s

And finally, as mentioned in the command output, login using faas-cli to be able to interact with your new OpenFaaS installation:

pi@raspberrypi:~ $ sudo cat /var/lib/faasd/secrets/basic-auth-password | faas-cli login -s
Calling the OpenFaaS server to validate the credentials...
WARNING! Communication is not secure, please consider using HTTPS. Letsencrypt.org offers free SSL/TLS certificates.
credentials saved for admin http://127.0.0.1:8080

Access the OpenFaaS interface

Once faasd is setup and running, the OpenFaaS user interface can be accessed on your browser at http://RASPBERRYPI_IP:8080. Since it is protected by basic auth, you would need to use the username and password available under /var/lib/faasd/secrets/basic-auth-password and /var/lib/faasd/secrets/basic-auth-user to login.

Once logged in, you will be greeted with the following interface:

OpenFaaS web interface

There are a few functions already available at the OpenFaas store, that you can easily deploy directly from the web user interface. Let's try deploying the figlet function:

Deploy the figlet function

Once the status of the function is Ready, let's try to invoke it:

Using faas-cli

Let's use faas-cli now to interact with the OpenFaas gateway. First, we need to login to the OpenFaas gateway using the faas login command from our workstation.

Fetch the password from the /var/lib/faasd/secrets/basic-auth-password file on the Raspberry Pi and store it in a file on your workstation because it's required for the login. Here, I have stored the password in the ~/.faas_pass file:

$ cat ~/.faas_pass | faas login -s --gateway http://raspberrypi.loc:8080  
Calling the OpenFaaS server to validate the credentials...
WARNING! Communication is not secure, please consider using HTTPS. Letsencrypt.org offers free SSL/TLS certificates.
credentials saved for admin http://raspberrypi.loc:8080

We can list and inspect the deployed functions using the commands below:

$ faas list --gateway http://raspberrypi.loc:8080
Function Invocations Replicas
figlet 1 1    

$ faas describe --gateway http://raspberrypi.loc:8080 figlet
Name: figlet
Status: Ready
Replicas: 1
Available replicas: 1
Invocations: 1
Image:               
Function process:    
URL: http://raspberrypi.loc:8080/function/figlet
Async URL: http://raspberrypi.loc:8080/async-function/figlet

Using `faas-cli` to deploy a function from the store

We can list the available function in the OpenFaas store for the armhf platform using the command below:

$ faas store list --platform armhf

FUNCTION DESCRIPTION
NodeInfo Get info about the machine that you...
Figlet Generate ASCII logos with the figlet CLI
SSL/TLS cert info Returns SSL/TLS certificate informati...
YouTube Video Downloader Download YouTube videos as a function
OpenFaaS Text-to-Speech Generate an MP3 of text using Google'...
nslookup Uses nslookup to return any IP addres...
Docker Image Manifest Query Query an image on the Docker Hub for ...
Left-Pad left-pad on OpenFaaS
Identicon Generator Create an identicon from a provided s...

Let's deploy the nslookup function using the faas store deploy command:

$ faas store deploy --platform armhf --gateway http://raspberrypi.loc:8080 nslookup
WARNING! Communication is not secure, please consider using HTTPS. Letsencrypt.org offers free SSL/TLS certificates.

Deployed. 200 OK.
URL: http://raspberrypi.loc:8080/function/nslookup

$ faas describe nslookup --gateway http://raspberrypi.loc:8080
Name: nslookup
Status: Ready
Replicas: 1
Available replicas: 1
Invocations: 0
Image:               
Function process:    
URL: http://raspberrypi.loc:8080/function/nslookup
Async URL: http://raspberrypi.loc:8080/async-function/nslookup

Let's invoke our new function from the command line:

$ echo "openfaas.com" | faas invoke nslookup --gateway http://raspberrypi.loc:8080 
nslookup: can't resolve '(null)': Name does not resolve

Name: openfaas.com
Address 1: 185.199.108.153
Address 2: 185.199.111.153
Address 3: 185.199.109.153
Address 4: 185.199.110.153

Voila! We have deployed and tested our first function from the command line. 🎉

Build your own function

What if we want to build a new function ourserlves, and deploy it to OpenFaas on the Raspberry PI?

faas-cli offers a convenient way to achieve this, as it provides templates for multiple programming languages and commands that allow us to build and deploy new functions to OpenFaas.

However, since we don't have Docker installed on the Rapsberry Pi, we would need to build our functions using another tool: buildkit.

Download buildkit binaries

Since buildkit binaries for armv7 are already available on the project's Github repository, we won't need to compile them by ourselves. Let's fetch the latest buildkit binaries on the RPi:

pi@raspberrypi:~ $ wget -qO- https://github.com/moby/buildkit/releases/download/v0.6.4/buildkit-v0.6.4.linux-arm-v7.tar.gz | sudo tar -xz -C /usr/local/bin/ --strip-components=1 
pi@raspberrypi:~ $ /usr/local/bin/buildkitd --version 
buildkitd github.com/moby/buildkit v0.6.4 ebcef1f69af0bbca077efa9a960a481e579a0e89
pi@raspberrypi:~ $ /usr/local/bin/buildctl --version 
buildctl github.com/moby/buildkit v0.6.4 ebcef1f69af0bbca077efa9a960a481e579a0e89

Build a new function

We are going to build a small function in golang and deploy it to OpenFaas.

Luckily, we don't have to do everything from scratch. We can use one of the already available templates from the OpenFaas template store.

We can list the templates available for the armhf platform using the command below:

pi@raspberrypi:~ $ faas template store list --platform armhf 

NAME SOURCE DESCRIPTION
dockerfile-armhf openfaas Classic Dockerfile armhf template
go-armhf openfaas Classic Golang armhf template
node-armhf openfaas Classic NodeJS 8 armhf template
python-armhf openfaas Classic Python 2.7 armhf template
python3-armhf openfaas Classic Python 3.6 armhf template
node10-express-armhf openfaas-incubator Node.js 10 powered by express armhf template
python3-flask-armhf openfaas-incubator Python 3.6 Flask armhf template
python3-http-armhf openfaas-incubator Python 3.6 with Flask and HTTP for ARMHF
node8-express-armhf openfaas-incubator Node.js 8 powered by express armhf template
golang-http-armhf openfaas-incubator Golang HTTP armhf template
golang-middleware-armhf openfaas-incubator Golang Middleware armhf template

We're going to use the classic golang template here, so let's create a new function:

pi@raspberrypi:~ $ mkdir ~/openfaas && cd ~/openfaas
pi@raspberrypi:~/openfaas $ faas new hello-go --lang go-armhf --prefix myedes
Folder: hello-go created.
  ________  ____
 / _ \ _ _____ _ __|___ |_ _ ___/___ |
| | | | '_ \ / _ \ '_ \| |_ / _` |/ _` \___ \
| |_| | |_) | __/ | | | _| (_| | (_| |___) |
 \ ___/| .__ / \ ___|_| |_|_| \__ ,_|\ __,_|____ /
      |_|

Function created in folder: hello-go
Stack file written: hello-go.yml

Notes:
You have created a new function which uses Golang 1.11
To include third-party dependencies, use a vendoring tool like dep:
dep documentation: https://github.com/golang/dep#installation

You may also like the golang-middleware and golang-http templates
available via "faas-cli template store"

The --prefix option allows you to specify a custom docker registry used to pushing and pulling the function's image.

The template we have used consists of a simple go function that returns a text message along with the request body. The logic can be found inside the hello-go/handler.go file:

pi@raspberrypi:~/openfaas $ cat hello-go/handler.go 
package function

import (
    "fmt"
)

// Handle a serverless request
func Handle(req []byte) string {
    return fmt.Sprintf("Hello, Go. You said: %s", string(req))
}

Using the --shrinkwrap option, we can generate the build context for our function without actually building our function's image. This is useful when we want to use a different tool for building our image, in our case buildkit:

pi@raspberrypi:~/openfaas $ faas build -f hello-go.yml --shrinkwrap 
[0] > Building hello-go.
Clearing temporary build folder: ./build/hello-go/
Preparing: ./hello-go/ build/hello-go/function
Building: docker.io/myedes/hello-go:latest with go-armhf template. Please wait..
hello-go shrink-wrapped to ./build/hello-go/
[0] < Building hello-go done in 0.01s.
[0] Worker done.

Total build time: 0.01s

As we can see, the command generated a few files inside the build/ folder; our build context:

build/
└── hello-go
    ├── Dockerfile
    ├── function
    │   └── handler.go
    ├── go.mod
    ├── main.go
    └── template.yml

2 directories, 5 files

Before building our image, we need to configure the authentication to be able to push to the docker registry. However, we cannot use the docker login command since we don't have Docker installed, so we will have to create the ~/.docker/config.json file manually.

For Docker Hub , we need to generate a token from the user interface and then create the ~/.docker/config.json on the RPi as follows:

pi@raspberrypi:~/openfaas $ export DOCKERHUB_USERNAME=myedes
pi@raspberrypi:~/openfaas $ export DOCKERHUB_TOKEN=<PERSONAL ACCESS TOKEN>
pi@raspberrypi:~/openfaas $ export DOCKER_AUTH=$(echo -n "$DOCKERHUB_USERNAME:$DOCKERHUB_TOKEN" | base64)

pi@raspberrypi:~/openfaas $ cat > ~/.docker/config.json << EOF 
{
    "auths": {
        "https://index.docker.io/v1/": {
            "auth": "$DOCKER_AUTH"
        }
    }
}
EOF

Let's start the buildkitd daemon in the background, and then start the build:

# Run the buildkitd daemon
pi@raspberrypi:~/openfaas $ sudo /usr/local/bin/buildkitd & 
[1] 15587

# Build and push the function image to hub.docker.com
pi@raspberrypi:~/openfaas $ sudo buildctl build \
    --frontend dockerfile.v0 \
    --local context=build/hello-go/ \
    --local dockerfile=build/hello-go/ \
    --output type=image,name=docker.io/myedes/hello-go:latest,push=true

[+] Building 81.3s (26/26) FINISHED
...
 => => pushing layers
 => => pushing manifest for docker.io/myedes/hello-go:latest

For more information about how to use buildkit, make sure to check out the moby/buildkit Github repository.

Deploy the function

As we have built and pushed the function's image to the registry, we can now go ahead and deploy our new function to our OpenFaas gateway:

pi@raspberrypi:~/openfaas $ faas deploy -f hello-go.yml 
Deploying: hello-go.
WARNING! Communication is not secure, please consider using HTTPS. Letsencrypt.org offers free SSL/TLS certificates.

Deployed. 200 OK.
URL: http://127.0.0.1:8080/function/hello-go

By inspecting our new function, we can see that it's in a "Ready" state:

pi@raspberrypi:~/openfaas $ faas describe hello-go 
Name: hello-go
Status: Ready
Replicas: 1
Available replicas: 1
Invocations: 0
Image:               
Function process:    
URL: http://127.0.0.1:8080/function/hello-go
Async URL: http://127.0.0.1:8080/async-function/hello-go

We can now invoke it using the faas invoke command from the Raspberry Pi:

pi@raspberrypi:~/openfaas $ echo "Hello OpenFaas" | faas invoke hello-go 
Hello, Go. You said: Hello OpenFaas

or from our workstation, but we need to specify the gateway using the --gateway parameter:

$ echo "Hello from laptop" | faas invoke --gateway http://raspberrypi.loc:8080 hello-go

Hello, Go. You said: Hello from laptop

And that's it, we have built and deployed our first function to OpenFaas running on a single Raspberry PI 🎉 Pretty cool isn't it?

Conclusion

In this blog post, we have gone through how we can run a FaaS serverless platform based on OpenFaas on a Raspberry Pi board, and how to build and deploy a simple function.

Although faasd is still a bit limited in its features compared to OpenFaas, it is very useful for small setups like home labs especially that there is no need to maintain a Kubernetes or Docker Swarm cluster

Finally, kudos to @alexellisuk and the OpenFaas team for this awesome project!

References:

How I prepared & passed the Certified Kubernetes Administrator (CKA) Exam

Mehdi Yedes — Wed, 29 Jan 2020 09:45:23 +0000

Finishing the year as a Certified Kubernetes Administrator(CKA) was my personal goal for 2019, and I was able to take the exam around the end of the year and pass with a score of 91%. 🎉

In this blog post, I wanted to share some useful resources that helped me pass the CKA exam, and a few tips that can help you prepare and hopefully pass if you are also planning to take it.

DISCLAIMER: This post is a bit long because I tried to dump all the knowledge and experience I gathered when preparing for the CKA exam. So brace yourself 😀

The Certified Kubernetes Administrator Exam

With the exploding adoption of Kubernetes, the Certified Kubernetes Administrator program was created by the Cloud Native Computing Foundation(CNCF) in collaboration with the Linux Foundation to allow Kubernetes users to demonstrate that they have the necessary skills and knowledge to perform the tasks and responsibilities of a Kubernetes administrator.

The exam's format

The good thing about it is that it's 100% hands-on. It's an online proctored exam where you are asked to perform certain tasks on the command line.

The Candidate Handbook is your definitive source for any details about the exam. So make sure to read it thoroughly.

Here is a short list of points worth mentioning:

You need a steady internet connection.
You would need a webcam and a microphone which are required by the proctor.
You would need a government issued ID , or a passport.
The exam consists of 24 questions that you can solve in no specific order.
The duration of the exam is 3 hours.
The pass mark is 74%.
You need to use the Chrome browser.
You have one free retake in case you don't pass on your first try 🎉

The curriculum

Unlike the Certified Kubernetes Application Developer(CKAD) exam, the CKA exam focuses more on cluster administration rather than deploying and managing applications on Kubernetes.

The exam's curriculum is usually updated quarterly, you can always find the latest version on Github at cncf/curriculum.

The CKA exam covers the following topics:

Application Lifecycle Management – 8%
Installation, Configuration & Validation – 12%
Core Concepts – 19%
Networking – 11%
Scheduling – 5%
Security – 12%
Cluster Maintenance – 11%
Logging / Monitoring – 5%
Storage – 7%
Troubleshooting – 10%

The exam environment

The day of the exam, you will have multiple cluster presented for you, and with each question you will be provided with name of the cluster where you should try to solve the question.

Below is the list of the clusters provided to the candidate from the latest Exam Tips document available at the CKA CNCF page at the time of writing this post:

Cluster	Members	CNI	Description
k8s	1 master, 2 workers	flannel	k8s cluster
hk8s	1 master, 2 workers	calico	k8s cluster
bk8s	1 master, 1 worker	flannel	k8s cluster
wk8s	1 master, 2 workers	flannel	k8s cluster
ek8s	1 master, 2 workers	flannel	k8s cluster
ik8s	1 master, 1 base node	loopback	k8s cluster - missing worker node

The Kubernetes version running on the exam environment is currently v1.16 at the time of writing this post, and the Linux distribution is Ubuntu 16.

Preparing for the exam

The first step in preparing for the CKA exam(or any exam) is understanding what it is about.

So make sure to read all the documents provided in the CKA Program page at https://www.cncf.io/certification/cka/ :

Pre-requisites

Although the CKA exam is about Kubernetes, it also requires some basic sysadmin skills. So, you need be comfortable with the Linux command line and have a minimum knowledge on how to use the following tools:

systemd for managing system services. Basic knowledge would be enough IMHO, but very important especially for troubleshooting cluster components. There is a nice tutorial series for that provided by the DigitalOcean people: Systemd Essentials: Working with Services, Units, and the Journal
vim for editing files on the command line. Although you could change the default text editor by setting the value of $EDITOR to nano if that's what you are most comfortable with, vim can give you a productive boost during the exam.
tmux since you only get one console during the exam, being able to have multiple panes open at the same time might be helpful. Personally, I didn't really need or use tmux during the exam, so if you don't use it already in your day to day work, I don't recommend learning it for the sake of the exam.
openssl for generating keys, CSRs, certificates etc.. You will probably need it during the exam for security related questions. So make sure you train yourself to use it at least for those basic use cases.

Getting ready for the exam

In this section, I am going to provide some tips on how to prepare for the exam and also list some useful resources that helped me and might help you get fit for the exam day.

kubectl

Since the CKA exam is 100% practical, you need to make sure you are confident enough with kubectl. That's mostly what you will be using during the exam, and since you are already reading this post, chances are you are already using kubectl or at least experimenting with it.

You need to be quick on the command line since you will have limited time for solving the questions during the exam, so knowing how to perform the following quickly with kubectl is crucial:

Checking the config, switching and creating contexts
Creating, editing and deleting kubernetes resources
Viewing, finding and inspecting resources
Updating and patching resources
Interacting with pods, nodes and cluster

A lot of useful kubectl command examples can be found in the kubectl cheatsheet available in the official kubernetes documentation.

It is also very useful to know how to use the kubectl run command to create resources quickly, saving time by avoiding to write yaml files(who likes that, right?). You can also use it to generate yaml files if you need to edit something before actually creating the kubernetes object by using the --dry-run and the -o yaml options combined. Some details about the kubectl run usage can be found here.

If you come from the Docker world and still starting with Kubernetes, then the kubectl for Docker Users documentation page is definitely worth checking out.

Getting familiar with JSONPath template would be also helpful. Combining kubectl and jsonpath enables you to easily extract resource information in a format that you can specify.

Finally, make sure to practice a lot with kubectl, whether it is on local kubernetes clusters with minikube, docker-desktop or on the cloud. That is very crucial for the exam.

Learning resources

If you are planning to take the CKA exam, them you probably have already searched around the internet for some resources and found plenty. So in this section, I am only going to list the resources that I have found most informative and helpful for me to pass the exam.

The Kubernetes Documentation

The most important resource is the official kubernetes documentation; that's your definitive source of information. And since you are allowed to access it during the exam, it's really important that you know how to easily navigate it and quickly search for what you need. Make sure to get well accustomed to it.

Also, make sure you get to do most if not all of the tasks listed here.

It's really useful to join the kubernetes slack community at https://slack.k8s.io/. There is a slack channel dedicated to CKA exam questions named #cka-exam-prep.

The members there are really nice and helpful and would answer any questions you have.

Kubernetes The Hard Way(KTHW)

The kubernetes-the-hard-way repo was created by Kelsey Hightower to provide a guide for bootstrapping a Kubernetes cluster on Google Cloud Platform. It helps you understand the internals of a Kubernetes cluster, which would be really important especially for troubleshooting.

Make sure to go through it at least once while trying to understand every step on the way.

If you don't want to use GCP, there is another fork that relies on vagrant and can be found here:

Bootstrap Kubernetes the hard way on Vagrant on Local Machine. No scripts.

Online Courses

There are a couple of online course available that can help you prepare for the CKA exam.

I was able to try 3 of them while preparing for the exam:

Kubernetes Fundamentals (LFS258) which was part of the CKA exam bundle I purchased. I only liked the practice labs, otherwise the course was very boring and you'd better read the kubernetes documentation rather than reading slides. So IMHO totally not worth taking.
Linuxacademy: Cloud Native Certified Kubernetes Administrator (CKA): I found this course really good at first. However, after a while I found myself watching the instructor mostly typing commands in the terminal so I got disconnected and stopped following the course. I also tried the mock exams, but I found them a bit limited.
Udemy: Certified Kubernetes Administrator (CKA) with Practice Tests This was the most comprehensive course for me in this list. It covered all the topics, and the instructor made sure to explain all the Kubernetes concepts(and also other concepts) thouroughly. The practice labs are really good since you are provided with an environment and your answers are checked there automatically. The mock exams were also a great preparation for the exam. I cannot recommend this course enough!

Additional Resources

The Kubernetes in Action book by Marko Lukša is definitely worth reading to have a good understanding of Kubernetes.

There is a google spreadsheet created by the community that compiles a lot of useful resources that can be found here.

Some additional useful Github repositories:

Tips for the exam day

In this section, I am going to provide a few tips for the day of the exam:

You are allowed to open one additional browser tab in addition to the exam interface and you can use it to browse the kubernetes documentation. Bookmarks are also allowed, so make sure to create some bookmarks in chromes for the documentation sections that you think you would need in the exam beforehand.
You don't have to solve the questions in a specific order. So you can start with the easiest to build some confidence, but that's a matter of personal preference.
There is built-in notepad in the exam interface which might be handy since you're not allowed to write on paper during the exam. You can use it to write the questions' numbers so that you keep track of the ones you didn't solve and get back to them later.
If you are taking the exam with a laptop, use an external monitor if your laptop screen is tiny. You would need all the space you can get for the terminal.
Make sure to go to the restroom before starting the exam. During the 3 hours, you would only be able to take a break if your proctor allows it but the timer would never stop for you.
Have some water in a bottle without a label, or a transparent glass. Anything other than that is not allowed.
Take the exam in a quiet room, on a clean desk. Remove any electronics from the desk and make sure that absolutely no one enters the room during the exam. You will be asked by the proctor to show him around the room using the webcam.
Finally: GOOD LUCK!

Conclusion

In this post, I tried to provide some tips and resources for preparing the CKA exam based on my experience.

I hope this article would be useful for you and please let me know in the comments if it somehow helped you to pass the exam.

This post was originally published at: https://myedes.io/cka-exam-tips/

DEV Community: Mehdi Yedes

Tracking Stripe Payments with Slack and faasd

The architecture

Preparing the Setup

Obtain an exit node with inlets

Add a Stripe Webhook

Create a Slack App

Create a function to receive webhooks from Stripe

Building & deploying the function

Test the function

Conclusion

Turn your Raspberry Pi into a serverless platform with faasd

Installing dependencies

Install containerd

Setup container networking

Install faasd

Install faas-cli

Install faasd

Access the OpenFaaS interface

Using faas-cli

Using faas-cli to deploy a function from the store

Build your own function

Download buildkit binaries

Build a new function

Deploy the function

Conclusion

References:

How I prepared & passed the Certified Kubernetes Administrator (CKA) Exam

The Certified Kubernetes Administrator Exam

The exam's format

The curriculum

The exam environment

Preparing for the exam

Pre-requisites

Getting ready for the exam

kubectl

Learning resources

Tips for the exam day

Conclusion

Install `faas-cli`

Install `faasd`

Using `faas-cli` to deploy a function from the store