Flink SQL Examples

This repository contains assets for running Flink SQL examples that start with one or more streams of data in Apache Kafka topics, run a Flink SQL job and result in one or more streams of data sent to Apache Kafka topics.

The data-generator module contains an application that can provide the streams of data for the different examples.

Setting up the environment for running an example

Prerequisites

• Kubernetes cluster
  • If you are using minikube we recommend the following resources as a minimum:

    MINIKUBE_CPUS=4
    MINIKUBE_MEMORY=16384
    MINIKUBE_DISK_SIZE=25GB
    

• kubectl CLI or equivalent
  • For example, if you are using RedHat OpenShift you can substitute kubectl for oc in the instructions
• docker or podman

Building the data-generator application

The container image for the data-generator application is in quay.io, however you can build the image yourself. If you choose to do this make sure you update the data-generator.yaml file for the example to point to your new image.

1. Build the application:

   mvn clean package
   

2. Build the image:

   ${BUILD_COMMAND} -t flink-examples-data-generator:latest data-generator
   

Installing Apache Kafka, Apache Flink and Apicurio Registry

1. Create a flink namespace:

   kubectl create namespace flink
   

2. Apply the Strimzi QuickStart:

   kubectl create -f 'https://strimzi.io/install/latest?namespace=flink' -n flink
   

3. Create an Apache Kafka cluster:

   kubectl apply -f https://strimzi.io/examples/latest/kafka/kraft/kafka-single-node.yaml -n flink 
   

4. Install Apicurio Registry:

   kubectl apply -f apicurio-registry.yaml -n flink
   

5. Install cert-manager (this creates cert-manager in a namespace called cert-manager):

   kubectl create -f https://github.com/jetstack/cert-manager/releases/download/v1.15.2/cert-manager.yaml
   kubectl wait deployment --all  --for=condition=Available=True --timeout=300s -n cert-manager
   

6. Deploy Flink Kubernetes Operator 1.10.0 (the latest stable version):

   helm repo add flink-operator-repo https://downloads.apache.org/flink/flink-kubernetes-operator-1.10.0/
   helm install flink-kubernetes-operator flink-operator-repo/flink-kubernetes-operator \
   --set podSecurityContext=null \
   --set defaultConfiguration."log4j-operator\.properties"=monitorInterval\=30 \
   --set defaultConfiguration."log4j-console\.properties"=monitorInterval\=30 \
   -n flink
   

   Note:
   (1) Set podSecurityContext to null so that we can run in OpenShift environment
   (2) Set monitorInterval to log4j properties file so that we can dynamically change log level for operator and job/task manager.

Running an example

The steps to run each example are described in their own README. Make sure you have already installed Apache Kafka, Apache Flink and Apicurio Registry.

Running an example in other namespace

By default, we assume all the jobs are running in flink namespace, but it is also possible to run jobs in other namespaces. Please see here for more information.

Viewing the Apicurio Registry UI

The source topics for the example will contain Avro records. You can view the Apicurio Registry UI by running kubectl port-forward service/apicurio-registry-service 8080 -n flink and visiting http://localhost:8080/ui in a browser.

Changing log level dynamically

Since the monitorInterval has been set via helm install command above, we can change the log level via updating/patching the config map directly. To change the operator log level, run kubectl edit cm flink-operator-config -n flink and update the log4j-operator.properties section. To change the job/task manager log level, find the config map for the application and edit it. For example: run kubectl edit cm flink-config-recommendation-app -n flink for recommendation-app example and update the log4j-console.properties section.

Running the data-generator without a schema registry

It is possible to run the data-generator so that it produces CSV records, rather than Avro records. In the <EXAMPLE_DIRECTORY>/data-generator.yaml file change the USE_APICURIO_REGISTRY to false. In the SQL statements supplied in the args in the <EXAMPLE_DIRECTORY>/flink-deployment.yaml, switch to using CSV:

• Change 'value.format' = 'avro-confluent' to 'format' = 'csv'.
• Remove value.avro-confluent.schema-registry.url.

Releasing

See RELEASING.md for instructions on how to release.