Creating and Testing Serverless Functions

Usage Scenario

You are a developer who needs to create an API to receive and process data. You have heard of the approach to use Serverless Functions to implement such an API, so you want to learn how to create a Serverless Function and how to use it.

Task Flow

In this exercise, you will perform the following steps:

Create a Serverless Function using kubectl.
Create a Serverless Function using Kyma dashboard.
Expose and test the Function using HTTP.

Prerequisites

You have created a SAP BTP, Kyma runtime instance in the SAP BTP subaccount. See Deploying a Kubernetes Cluster with Kyma on SAP BTP.
You have configured kubectl to interact with your SAP BTP, Kyma runtime instance, and you have access to Kyma dashboard. See Setting and Configuring Kubectl for Kyma and Accessing Your Kyma Runtime Instance Using Kyma Dashboard.
You have added the Serverless module. See Adding Kyma Modules.

Task 1: Create and Test a Serverless Function

Steps

Create a Serverless Function using kubectl.
1. Open your terminal and list all current Serverless Functions in your default namespace:
  Code Snippet
```
1
kubectl get functions
```
  If your namespace has no Functions, you get an empty list.
2. Enable the Istio sidecar proxy injection in the default namespace.
  Code Snippet
```
1
kubectl label namespace default istio-injection=enabled --overwrite
```
  If you create a Function in a namespace with enabled Istio sidecar injection, an Istio sidecar proxy is automatically injected to the Function's Pod during its creation. This makes the Function part of the Istio service mesh. To expose a workload using an APIRule custom resource, which you will do in step 3, it is required to include the workload in the Istio service mesh.
3. To create a Serverless Function, run the following command:
  Code Snippet
```
1
kubectl apply -n default -f https://raw.githubusercontent.com/sap-samples/kyma-runtime-learning-journey/main/unit_3/functions/hello-world-function.yaml
```
  If successful, you get the output: function.serverless.kyma-project.io/hello-world-function created.
4. List all s in the default namespace again:
  Code Snippet
```
1
kubectl get functions
```
  The Function hello-world-function is on the list.
Create a Serverless Function using Kyma dashboard.
1. Open Kyma dashboard, go to Namespaces, and choose default.
2. Go to Workloads → Functions and choose Create.
3. Enter the following information:
  - Name: hello-kyma-function
  - Language: JavaScript
  You can also switch to the YAML tab to see, copy, or edit the YAML manifest of the Function.
4. Choose the Create button.
  Result
  Your function is now being created. After a few seconds, it has the status Running.
Expose and test the Function using HTTP.
Note
Exposing the Function using HTTP allows you to test it in a browser. You will find out more about exposure later in the course.
1. Go to the Kyma Environment section of your subaccount overview to check the default domain of your Kyma cluster.
  Copy the value of APIServerURL after https://api. For example, for the URL https://api.xxx123.kyma.ondemand.com, copy xxx123.kyma.ondemand.com.
2. Go to Discovery and Network→API Rules and choose Create.
3. Enter the following information and choose the Create button:
  - Name: hello-kyma-function-api
  - Service Name: hello-kyma-function
  - Port: 80
  - Host: hello-kyma-function-api.<your-domain>
    Replace <your-domain> with the copied domain name.
  - Access Strategy: No Auth
  By creating this APIRule CR, you expose your function as an HTTP endpoint. Only GET requests are allowed.
4. Paste the URL hello-kyma-function-api.<your-domain> in your browser.
  Result
  You get the following message:
  Hello world from the Kyma Function hello-kyma-function running on nodejs20!

Result

Bravo, you have successfully created and tested a Serverless Function!