CloudEvent to Slack OpenFaaS Demo

This repo contains a simple OpenFaaS function which demonstrates how events using the CloudEvents 0.1 Specification schema can be consumed from Azure EventGrid.

The demo function handles the receipt of a Microsoft.Storage.BlobCreated event in CloudEvents0.1 format, where it will parse the received message, extracting the URL of the created file from the CloudEvent and sending both that URL and the raw CloudEvent message to a configurable Slack Channel for display.

Building the function

The following steps are optional, you can proceed to Deploying the function if you wish to use the prebuilt image. You should also have a look at OpenFaaS Cloud as it can be used for a hosted GitOps build and deployment flow.

1. git clone https://github.com/johnmccabe/cloudevents-slack-demo.git

2. cd cloudevents-slack-demo

3. faas build

4. If you are making the image public you can also push it to your registry.

   faas push
   

Deploying the function

1. Create a secret containing your Slack token, for example on Swarm or Kubernetes.

   echo <slack token> | docker secret create cloudevent-slack-token -
   kubectl create secret generic secret-api-key --from-file=cloudevent-slack-token=<slack token file> --namespace openfaas-fn
   

2. Replace <SLACK_ROOM_ID> with your Slack room id in stack.yml

3. Deploy the function to your OpenFaaS platform

   faas deploy
   

4. You can now use the deployed functions endpoint in your EventGrid subscription for the Storage event, making sure to set the scheme to --event-delivery-schema cloudeventv01schema. For example:

   az eventgrid event-subscription create \
       --resource-id $storageid \
       --name openfaas-cloudevent-demo \
       --endpoint https://xxxxxxxx.ngrok.io/function/cloudevents-slack-demo \
       --event-delivery-schema cloudeventv01schema
   

Handling a CloudEvent in OpenFaaS

The function handler converts the received raw request into a CloudEvent as follows (with the implementation in cloudevent.go):

c, err := getCloudEvent(req)
if err != nil {
    log.Fatal(err)
}

Should the received event not be of type CloudEvent the function will exit and an error logged.

Azure and Slack Handling

The demo handler includes two other Slack/Azure related parts which:

• Responds to an EventGrid Subscription Validation Event to validate the function endpoint for subsequent delivery of events.

  if resp := azureValidationEvent(req); resp != nil {
      return *resp
  }
  

  This is received from EventGrid when setting up the subscription.

• Checks the CloudEvents EventType to determine how to interpret the Data payload, in this case it expects a MicrosoftStorageBlobCreatedType event payload which it uses to send a message to Slack with sendmessage()