Call a Registered External Service from Kyma

This guide shows how to call a registered external service from Kyma using a simple Function.

Prerequisites

• A registered external service

• Your service display name exported as an environment variable

• Your Application name exported as an environment variable

• Your desired namespace, cluster domain, and the names for your Function and APIRule exported as environment variables

  export NAMESPACE=default
  export CLUSTER_DOMAIN=local.kyma.dev
  export FUNCTION_NAME=my-function
  export APIRULE_NAME=$FUNCTION_NAME-ar

• Istio sidecar injection enabled in your namespace

  kubectl label namespace $NAMESPACE istio-injection=enabled

WARNING

On a local Kyma deployment, skip SSL certificate verification when making a curl call, by adding the -k flag to it. Alternatively, add the Kyma certificates to your local certificate storage on your machine using the kyma import certs command.

Steps

1. Build a path to access your registered service:

   export GATEWAY_URL=http://central-application-gateway.kyma-system:8080/$APP_NAME/$SERVICE_DISPLAY_NAME

   WARNING

   SERVICE_DISPLAY_NAME in the GATEWAY_URL path must be in its normalized form. This means that, for example, if you used test-basic-auth as the service displayName, you're good to go, but if you used "Test Basic Auth", you must replace it with test-basic-auth in the path.

2. Create a Function that sends a request to the registered service with the additional path of /uuid. A successful response returns a UUID generated by httpbin.org. To create and register the Function in the desired namespace, run:

   cat <<EOF | kubectl apply -f -
   apiVersion: serverless.kyma-project.io/v1alpha2
   kind: Function
   metadata:
     name: $FUNCTION_NAME
     namespace: $NAMESPACE
     labels:
       app: $APP_NAME
   spec:
     runtime: nodejs18
     source:
       inline:
         source: |-
          const request = require('request');
   
          module.exports = { main: function (event, context) {
           return new Promise((resolve, reject) => {
               const url = process.env.GATEWAY_URL + "/uuid";
               const options = {
                   url: url,
               };
   
               sendReq(url, resolve, reject)
           })
          } }
   
          function sendReq(url, resolve, reject) {
           request.get(url, { json: true }, (error, response, body) => {
               if(error){
                   resolve(error);
               }
               resolve(response.body);
           })
          }
         dependencies: |-
          {
           "name": "example-1",
           "version": "0.0.1",
           "dependencies": {
             "request": "^2.85.0"
           }
          }
     env:
     - name: GATEWAY_URL
       value: $GATEWAY_URL
   EOF

3. To expose the Function outside the cluster, create an APIRule custom resource.

   cat <<EOF | kubectl apply -f -
   apiVersion: gateway.kyma-project.io/v1beta1
   kind: APIRule
   metadata:
     name: $APIRULE_NAME
     namespace: $NAMESPACE
     labels:
       function: $FUNCTION_NAME
   spec:
     gateway: kyma-system/kyma-gateway
     host: $APIRULE_NAME.$CLUSTER_DOMAIN
     rules:
     - path: /.*
       accessStrategies:
       - config: {}
         handler: noop
       methods:
       - GET
     service:
       name: $FUNCTION_NAME
       port: 80
   EOF

4. To verify that everything was set up correctly, you can now call the Function through HTTPS:

   curl https://$APIRULE_NAME.$CLUSTER_DOMAIN/

   NOTE

   If you get nothing or no healthy upstream as a response, wait for a few moments for the Function to get ready and call it again.

   A successful response returns a UUID generated by httpbin.org:

   {
     "uuid": "d44cc373-b26e-4a36-9890-6418d131a285"
   }