Triggering IBM Cloud Functions with Message Hub records

Create Message Hub data processing apps with IBM Cloud Functions powered by Apache OpenWhisk. This tutorial should take about 5 minutes to complete. After this, move on to more complex serverless applications such as those tagged openwhisk-hands-on-demo.

If you're not familiar with the Cloud Functions/OpenWhisk programming model try the action, trigger, and rule sample first. You'll need an IBM Cloud account and the latest OpenWhisk (wsk) or IBM Cloud command line plugin (bx wsk).

This example shows how to create an action that consumes Message Hub (Apache Kafka) messages (records).

1. Configure Message Hub
2. Create Cloud Function actions, triggers, and rules
3. Clean up

1. Configure Message Hub

Provision an IBM Message Hub service instance

Log into the IBM Cloud, provision a Message Hub instance, and name it openwhisk-kafka. On the "Manage" tab of the Message Hub console create a topic named "cats-topic". Set the corresponding names as environment variables in a terminal window:

export KAFKA_INSTANCE="openwhisk-kafka"
export KAFKA_TOPIC="cats-topic"

Import the service credentials into the OpenWhisk environment

We will make use of the built-in Cloud Functions Kafka package, which contains a set of actions and feeds that integrate with both Apache Kafka and IBM Message Hub (based on Kafka).

With Cloud Functions on the IBM Cloud, this package can be automatically configured with the credentials and connection information from the Message Hub instance we provisioned above. We make it available by refreshing our list of packages.

# Ensures the IBM Message Hub credentials are available to Cloud Functions.
wsk package refresh

2. Create Cloud Function actions, triggers, and rules

Attach a trigger to the Message Hub topic

Triggers can be explicitly fired by a user or fired on behalf of a user by an external event source, such as a feed. Use the code below to create a trigger to fire events when messages are received using the "messageHubFeed" provided in the Message Hub package.

# Create trigger to fire events when messages (records) are received
wsk trigger create message-received-trigger \
  --feed Bluemix_${KAFKA_INSTANCE}_Credentials-1/messageHubFeed \
  --param isJSONData true \
  --param topic "$KAFKA_TOPIC"

Create an action to process messages from the topic

Create a file named process-message.js. This file will define an action written as a JavaScript function. This function will print out messages that are received from Kafka. For this example, we are expecting a stream of messages that contain a cat object with name and color fields.

function main(params) {

  console.log(params);

  return new Promise(function(resolve, reject) {
    if (!params.messages || !params.messages[0] || !params.messages[0].value) {
      reject("Invalid arguments. Must include 'messages' JSON array with 'value' field");
    }
    var msgs = params.messages;
    var cats = [];
    for (var i = 0; i < msgs.length; i++) {
      var msg = msgs[i];
      for (var j = 0; j < msg.value.cats.length; j++) {
        var cat = msg.value.cats[j];
        console.log('A ' + cat.color + ' cat named ' + cat.name + ' was received.');
        cats.push(cat);
      }
    }
    resolve({
      "cats": cats
    });
  });

}

Deploy an IBM Cloud Function from the JavaScript file.

wsk action create process-message process-message.js

Map the action to the trigger with a rule

We are going to configure this action to be invoked in response to events fired by the message-received-trigger when messages are received on the Message Hub topic.

To do this, we create a rule, which maps triggers to actions. Once this rule is created, the process-message action will be executed whenever the message-received-trigger is fired in response to new messages being written to the Kafka stream.

wsk rule create log-message-rule message-received-trigger process-message

Enter data to fire a change

Begin streaming the Cloud Functions activation log in a second terminal window.

wsk activation poll

Now send a message to Message Hub using the message producer action back in the original window.

echo '{"cats": [{"name": "Tahoma", "color": "Tabby"}, {"name": "Tarball", "color": "Black"}] }' > records.json
DATA=$( base64 records.json )

wsk action invoke Bluemix_${KAFKA_INSTANCE}_Credentials-1/messageHubProduce \
  --param topic $KAFKA_TOPIC \
  --param value "$DATA" \
  --param base64DecodeValue true

View the log to look for the change notification. You should see activation records for the producing action, the rule, the trigger, and the consuming action.

3. Clean up

Remove the rule, trigger, action, and package

# Remove rule
wsk rule disable log-message-rule
wsk rule delete log-message-rule

# Remove trigger
wsk trigger delete message-received-trigger

# Remove actions
wsk action delete process-message

# Remove package
wsk package delete Bluemix_${KAFKA_INSTANCE}_Credentials-1

Troubleshooting

Check for errors first in the Cloud Functions activation log. Tail the log on the command line with wsk activation poll or drill into details visually with the Cloud Functions monitoring console.

If the error is not immediately obvious, make sure you have the latest version of the wsk CLI installed. If it's older than a few weeks, download an update.

wsk property get --cliversion

License

Apache 2.0