Kafka-connector

This is a Proof-of-Concept for connecting a number of Kakfa topics to OpenFaaS functions via the API Gateway.

Goals:

• Allow functions to subscribe to topics
• Ingest data from Kafka
• Work with black-box knowledge of OpenFaaS
• Formulate and validate a generic "connector-pattern" to be used for various event sources like Kafka, AWS SNS, RabbitMQ etc

Conceptual design

This diagram shows the Kafka connector on the left hand side. It is responsible for querying the API Gateway for a list of functions. It will then build up a map or table of which functions have advertised an interested in which topics.

When the connector hears a message on an advertised topic it will look that up in the reference table and find out which functions it needs to invoke. Functions are invoked only once and there is no re-try mechanism. The result is printed to the logs of the Kafka connector process.

The cache or list of functions <-> topics is refreshed on a periodic basis.

Try it out

This sample is setup for use on Swarm, but the application code will also work on Kubernetes by using the setup/kubernetes.yml file.

Usage for Swarm:

• Deploy this sample using ./build.sh
• Deploy or update a function so it has a label of topic=faas-request or some other topic

As an example:

$ faas store deploy figlet --label topic="faas-request"

The function can advertise more than one topic by using a comma-separated list i.e. topic=topic1,topic2,topic3

• Publish some messages to the topic in question i.e. faas-request

Instructions are below for publishing messages

• Watch the logs of the kafka-connector

Trigger a function via a topic with exec

You can use the kafka container to send a message to the topic.

SERVICE_NAME=kafka_kafka
TASK_ID=$(docker service ps --filter 'desired-state=running' $SERVICE_NAME -q)
CONTAINER_ID=$(docker inspect --format '{{ .Status.ContainerStatus.ContainerID }}' $TASK_ID)
docker exec -it $CONTAINER_ID kafka-console-producer --broker-list kafka:9092 --topic faas-request

hello world

Generate load on the topic

You can use the sample application in the producer folder to generate load for a topic.

Make sure you have some functions advertising an interest in that topic so that they receive the data.

Note: the producer must run inside the Kubernetes or Swarm cluster in order to be able to access the broker(s).

Monitor the results

Once you have generated some requests or start a load-test you can watch the function invocation rate increasing in Prometheus or watch the logs of the container.

Prometheus

You can open the Prometheus metrics or Grafana dashboard for OpenFaaS to see the functions being invoked.

Watch the logs

docker service logs kafka_connector -f

Topics
[__consumer_offsets faas-request] <nil>
2018/03/24 12:42:58 Binding to topics: [faas-request]
Rebalanced: &{Type:rebalance start Claimed:map[] Released:map[] Current:map[]}
Rebalanced: &{Type:rebalance OK Claimed:map[faas-request:[0]] Released:map[] Current:map[faas-request:[0]]}

2018/03/24 17:04:40 Syncing topic map
[#53694] Received on [faas-request,0]: 'Test the function.'
2018/03/24 17:04:41 Invoke function: figlet
2018/03/24 17:04:42 Response [200] from figlet  
|_   _|__  ___| |_  | |_| |__   ___   / _|_   _ _ __   ___| |_(_) ___  _ __    
  | |/ _ \/ __| __| | __| '_ \ / _ \ | |_| | | | '_ \ / __| __| |/ _ \| '_ \   
  | |  __/\__ \ |_  | |_| | | |  __/ |  _| |_| | | | | (__| |_| | (_) | | | |_ 
  |_|\___||___/\__|  \__|_| |_|\___| |_|  \__,_|_| |_|\___|\__|_|\___/|_| |_(_)
                  

Note: If the broker has a different name from kafka you can pass the broker_host environmental variable. This exclude the port.

Configuration

env_var	description
upstream_timeout	Go duration - maximum timeout for upstream function call
rebuild_interval	Go duration - interval for rebuilding function to topic map
topics	Topics to which the connector will bind
gateway_url	The URL for the API gateway i.e. http://gateway:8080
broker_host	Default is kafka
print_response	Default is false - this will output the response of calling a function in the logs