Super Simple Serverless eCommerce – Square Corner Blog – Medium


Serverless Functions using AWS Lambda

For our serverless function, we’ll process the Square catalog variant ID that is being sent from our form in our static site, and then create a checkout URL to redirect our user to. To do this, we’ll use Square’s JavaScript SDK inside our function to more easily generate the URL we need. You’re more than welcome to attempt using just AWS tools for creating and deploying the function, but we’re going to just use Serverless for managing deploying the function and linking it to AWS API Gateway.

If you, too, want to use serverless to create your own functions, they have great tutorials over here. You need to have Node on your machine and install serverless with npm install -g serverless (or if you don’t want it installed globally, just use npx).

You can run serverless create --template aws-nodejs to get a template going, but it creates a lot more than what’s needed. Feel free to just copy the handler.js and serverless.yml to modify into your own templates. We’ll start out with a basic function to test that our deployment is working as intended, then add in functionality for our checkout.

This is just our example to test. Next, we want to create our serverless.yml file for deploying our function and creating the AWS API Gateway endpoint.

There are probably more elegant ways of handling your credentials if you don’t want them in your file.

Now, it’s as simple as running serverless deploy to launch our functions into the cloud. You should see something similar to the below when you deploy:

Serverless: Packaging service...
Serverless: Excluding development dependencies...
Serverless: Uploading CloudFormation file to S3...
Serverless: Uploading artifacts...
Serverless: Uploading service .zip file to S3 (742.81 KB)...
Serverless: Validating template...
Serverless: Updating Stack...
Serverless: Checking Stack update progress...
..............
Serverless: Stack update finished...
Service Information
service: serverless-checkout
stage: prod
region: us-east-1
stack: serverless-checkout-prod
api keys:
None
endpoints:
ANY - https://UNIQUE_ID.execute-api.us-east-1.amazonaws.com/prod/checkout
functions:
checkout: serverless-checkout-prod-checkout
Serverless: Removing old service versions...

You should be able to visit the URL that Serverless logged out to the console in your browser and find our message, “Success! Our function is running!” showing up in the browser. We just need to refactor our Lambda function to handle the catalog variant ID in order to request our checkout URL and redirect the user.

Note that our credentials are pulled in from “process.env”, which can be set in the AWS console as environment variables.

Here we have our fully functioning (pun intended) Lambda function that can create checkout URLs to allow users to buy our products.

Again, it’s worth reminding that this is intentionally a minimal implementation that would only work for something like a digital good (that requires no tax), but demonstrates how easy it is to create your checkout and redirect a customer without having to spin up our own servers. In fact, if you were to append your catalog variant ID as query string parameters to your function URL, you could just parse those out in your function to essentially have your own serverless “buy it now” link. Additionally, you could add a line item for shipping costs to easily handle flat rate shipping and even capture the customer’s shipping details in the checkout (see here for more details on that).

A preview of our eCommerce store. Those are our stickers we give away at developer conferences.

Serverless Misunderstandings

There seems to be widespread misunderstanding around serverless computing and what it is comprised of. Is it pay per invocation? Pay per Mb/s of memory? Just like Node, serverless is suffering a bit from the same desire to “do all the things.” True, it’s a new technology that needs to be explored, but a lot of weird uses are cropping up that come across as anti-patterns (in my opinion). Node was and is known for being really bad at handling CPU-intensive tasks due to its single-threaded nature, and the same goes for using serverless for user facing interactions or APIs. Users expect things to be responsive, and cold starts kill the expected responsiveness. You can certainly try circumvent this by keeping your functions warm as a solution to this, but smells like an anti-pattern. The whole benefit of serverless is to not have to be as concerned with your infrastructure, yet people are writing more code to modify their infrastructure’s behavior that they don’t really have control over.

If you plan to use serverless for user-facing applications, look carefully at your user traffic patterns to your endpoints, since that would play heavily into overall user experience. A constant amount of traffic would be relatively fine — functions would stay warm and a very small percentage of users would be impacted by a slow response — but if you have particularly spiky traffic, the user experience will suffer as your platform provider is spinning up additional instances of your function to service your traffic.



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