Apache Camel source

These samples show how to configure Camel Sources. These event sources are highly dynamic and allow you to generate events from a variety of systems (cloud platforms, social networks, datastores, message brokers, legacy systems, etc.), leveraging all the 300+ components provided by Apache Camel.

All Camel Sources use Apache Camel K as the runtime engine.

Prerequisites

  1. Install Knative Serving and Eventing.

  2. Install the Apache Camel K Operator in any namespace where you want to run Camel sources.

    The preferred version that is compatible with Camel sources is Camel K v1.0.0-M4.

    Installation instructions are provided in the Apache Camel K Manual. Documentation includes specific instructions for common Kubernetes environments, including development clusters.

  3. Install the Camel Source from the camel.yaml in the Eventing Sources release page:

    kubectl apply --filename camel.yaml

Create Test Resources

All the CamelSource examples use some test resources for the purpose of displaying the generated events. The following resources need to be created:

  • a simple Knative event display service that prints incoming events to its log
  • an in-memory channel named camel-test that buffers events created by the event source
  • a subscription to direct events from the test channel to the event display service

Deploy the display_resources.yaml:

kubectl apply --filename display_resources.yaml

Run a Timer CamelSource

The samples directory contains some sample sources that can be used to generate events.

The simplest example of CamelSource, that does not require additional configuration, is the timer source.

The timer source periodically generates “Hello world!” events and forwards them to the provided destination.

If you want, you can customize the source behavior using options available in the Apache Camel documentation for the timer component. All Camel components are documented in the Apache Camel Website.

Install the timer CamelSource from source:

kubectl apply -f source_timer.yaml

Verify that the published events were sent into the Knative eventing system by looking at what is downstream of the CamelSource.

kubectl logs --selector serving.knative.dev/service=camel-event-display -c user-container

If you have deployed the timer source, you should see new log lines appearing every 3 seconds.

Run a MQTT CamelSource

One of the 300+ Camel components that you can leverage is Camel-Paho, based on the Eclipse Paho open source project.

A source based on Paho (like the provided MQTT CamelSource) allows to bridge any MQTT broker to a Knative resource, automatically converting IoT messages to Cloudevents.

To use the MQTT source, you need a MQTT broker running and reachable from your cluster. For example, it's possible to run a Mosquitto MQTT Broker for testing purposes.

First, edit the MQTT CamelSource and put the correct address of the MQTT broker in the brokerUrl field. You also need to provide the name of the topic that you want to subscribe to: just change paho:mytopic to match the topic that you want to use.

You can also scale this source out, in order to obtain more throughput, by changing the value of the replicas field. By default it creates 2 replicas for demonstration purposes.

To reduce noise in the event display, you can remove all previously created CamelSources from the namespace:

kubectl delete camelsource --all

Install the mqtt CamelSource:

kubectl apply -f source_mqtt.yaml

You can now send MQTT messages to your broker using your favourite client (you can even use Camel K for sending test events).

Each message you send to the MQTT broker will be printed by the event display as a Cloudevent.

You can verify that your messages reach the event display by checking its logs:

kubectl logs --selector serving.knative.dev/service=camel-event-display -c user-container

Run a Telegram CamelSource

Another useful component available with Camel is the Telegram component. It can be used to forward messages of a Telegram chat into Knative channels as events.

Before using the provided Telegram CamelSource example, you need to follow the instructions on the Telegram website for creating a Telegram Bot. The quickest way to create a bot is to contact the Bot Father, another Telegram Bot, using your preferred Telegram client (mobile or web). After you create the bot, you will receive an authorization token that is needed for the source to work.

First, edit the telegram CamelSource and put the authorization token, replacing the <put-your-token-here> placeholder.

To reduce noise in the event display, you can remove all previously created CamelSources from the namespace:

kubectl delete camelsource --all

Install the telegram CamelSource:

kubectl apply -f source_telegram.yaml

Now, you can contact your bot with any Telegram client. Each message you send to the bot will be printed by the event display as a Cloudevent.

You can verify that your messages reach the event display by checking its logs:

kubectl logs --selector serving.knative.dev/service=camel-event-display -c user-container

Run an HTTP Poller CamelSource

CamelSources are not limited to using a single Camel component. For example, you can combine the Camel Timer component with the Camel HTTP component to periodically fetch an external API, transform the result into a Cloudevent and forward it to a given destination.

The example will retrieve a static JSON file from a remote URL, but you can edit the HTTP poller CamelSource to add your own API.

If you have previously deployed other CamelSources, to reduce noise in the event display, you can remove them all from the namespace:

kubectl delete camelsource --all

Install the HTTP poller CamelSource:

kubectl apply -f source_http_poller.yaml

The event display will show some JSON data periodically pulled from the external REST API. To check the logs:

kubectl logs --selector serving.knative.dev/service=camel-event-display -c user-container