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Kafka

Kafka Cluster installation

For the installation Strimzi kafka operator will be used to deploy a Kafka cluster.

Strimzi Operator installation procedure using Helm

Installation using Helm (Release 3):

Step 1: Add the Strimzi Helm repository:

helm repo add strimzi https://strimzi.io/charts/

Step2: Fetch the latest charts from the repository:
```
helm repo update
```
Step 3: Create namespace
```
kubectl create namespace kafka
```

Step 3: Install Strimzi kafka operator

helm install strimzi-kafka-operator strimzi/strimzi-kafka-operator --namespace kafka

Step 4: Confirm that the deployment succeeded, run:
```
kubectl -n kafka get pod
```

Deploy Kafka cluster

Using Strimzi operator build Kafka cluster CRD.

Step 1: Create a manifest file deploying a 3 broker tls-encrypted cluster. It contains basic configuration of Kafka cluster with 3 Zookeeper replicas and 3 Kafka broker replicas. Persistence will be configure to use Longhorn as storageClass and 5GB of storage in the volume claims.

  apiVersion: kafka.strimzi.io/v1beta2
  kind: Kafka
  metadata:
    name: my-cluster
    namespace: kafka
  spec:
    kafka:
      version: 3.5.1
      replicas: 3
      listeners:
        - name: plain
          port: 9092
          type: internal
          tls: false
        - name: tls
          port: 9093
          type: internal
          tls: true
      config:
        offsets.topic.replication.factor: 3
        transaction.state.log.replication.factor: 3
        transaction.state.log.min.isr: 2
        default.replication.factor: 3
        min.insync.replicas: 2
        inter.broker.protocol.version: "3.5"
      storage:
        type: jbod
        volumes:
        - id: 0
          type: persistent-claim
        class: longhorn
          size: 5Gi
          deleteClaim: false

    zookeeper:
      replicas: 3
      storage:
        type: persistent-claim
        size: 5Gi
        deleteClaim: false5Gi
        class: longhorn
    entityOperator:
      topicOperator: {}
      userOperator: {}  

Step 2: Apply manifest
```
kubectl apply -f manifest.yml
```

Step 3: Check Kafka status

kubectl get kafka -n kafka
NAME         DESIRED KAFKA REPLICAS   DESIRED ZK REPLICAS   READY   WARNINGS
my-cluster   3                        3                     True

Note:

By default, intra-broker communication is encrypted with TLS while communication with ZooKeeper is both autenticated and encrypted with mTLS. The Apache ZooKeeper clusters backing the Kafka instances are not exposed outside of the Kubernetes cluster, providing additionnal security.

Create Topic

Step 1: Create a manifest file topic.yaml

apiVersion: kafka.strimzi.io/v1beta2
kind: KafkaTopic
metadata:
  name: my-topic
  labels:
    strimzi.io/cluster: my-cluster
spec:
  partitions: 1
  replicas: 3
  config:
    retention.ms: 7200000
    segment.bytes: 1073741824

Step 2: Apply manifest
```
kubectl apply -f topic.yml
```

Step 3: Check Kafka topic status

kubectl get kafkatopic my-topic -n kafka
NAME       CLUSTER      PARTITIONS   REPLICATION FACTOR   READY
my-topic   my-cluster   1            1                    True

Testing Kafka cluster

Once the cluster is running, you can run a simple producer to send messages to a Kafka topic (the topic will be automatically created).

Step 1: launch producer

kubectl -n kafka run kafka-producer -ti --image=quay.io/strimzi/kafka:0.29.0-kafka-3.2.0 --rm=true --restart=Never -- bin/kafka-console-producer.sh --bootstrap-server my-cluster-kafka-bootstrap:9092 --topic my-topic

Step 3: in a different terminal launch consumer

kubectl -n kafka run kafka-consumer -ti --image=quay.io/strimzi/kafka:0.29.0-kafka-3.2.0 --rm=true --restart=Never -- bin/kafka-console-consumer.sh --bootstrap-server my-cluster-kafka-bootstrap:9092 --topic my-topic --from-beginning

Step 5: In producer terminal wait for the prompt and start typing messages. (Input Control-C to finish)

Messages will be outputed in consumer terminal.

Schema Registry

A schema defines the structure of message data. It defines allowed data types, their format, and relationships. A schema acts as a blueprint for data, describing the structure of data records, the data types of individual fields, the relationships between fields, and any constraints or rules that apply to the data.

Kafka Schema Registry is a component in the Apache Kafka ecosystem that provides a centralized schema management service for Kafka producers and consumers. It allows producers to register schemas for the data they produce, and consumers to retrieve and use these schemas for data validation and deserialization. The Schema Registry helps ensure that data exchanged through Kafka is compliant with a predefined schema, enabling data consistency, compatibility, and evolution across different systems and applications.

Schema-Registry

Schema-Registry-and-Kafka

When using Avro or other schema format, it is critical to manage schemas and evolve them thoughtfully. Schema compatibility checking is enabled in Kafka Schema Registry by versioning every single schema and comparing new schemas to previous versions. The type of compatibility required (backward, forward, full, none, etc) determines how Kafka Schema Registry evaluates each new schema. New schemas that fail compatibility checks are removed from service.

Some key benefits of using Kafka Schema Registry include:

Schema Evolution: As data formats and requirements evolve over time, it is common for producers and consumers to undergo changes to their data schemas. Kafka Schema Registry provides support for schema evolution, allowing producers to register new versions of schemas while maintaining compatibility with existing consumers. Consumers can retrieve the appropriate schema version for deserialization, ensuring that data is processed correctly even when schema changes occur.
Data Validation: Kafka Schema Registry enables data validation by allowing producers to register schemas with predefined data types, field names, and other constraints. Consumers can then retrieve and use these schemas to validate incoming data, ensuring that data conforms to the expected structure and format. This helps prevent data processing errors and improves data quality. Schema Management: Kafka Schema Registry provides a centralized repository for managing schemas, making it easier to track, version, and manage changes. Producers and consumers can register, retrieve and manage schemas through a simple API, allowing for centralized schema governance and management.
Interoperability: Kafka Schema Registry promotes interoperability between different producers and consumers by providing a standardized way to define and manage data schemas. Producers and consumers written in different programming languages or using different serialization frameworks can use a common schema registry to ensure data consistency and compatibility across the ecosystem.
Backward and Forward Compatibility: Kafka Schema Registry allows producers to register backward and forward compatible schemas, enabling smooth upgrades and changes to data schemas without disrupting existing producers and consumers. Backward compatibility ensures that older consumers can still process data produced with a newer schema, while forward compatibility allows newer consumers to process data produced with an older schema.

Deploying Schema Registry

Official confluent docker images for Schema Registry can be installed using helm chart maintained by the community. Confluent official docker images support multiarchitecture (x86/ARM). However, this helm chart is quite old and it seems not to be maintaned any more (last update: 2 years ago).

Install Bitnami packaged Schema registry

Confluent Schema Registry packaged by Bitnami is keept up to date and it supports multi-architecture docker images.

Step 1: Prepare schema-registry-values.yaml:

kafka:
  enabled: false
auth:
  protocol: {}
service:
  ports:
    client: {}
externalKafka:
  brokers:
    - PLAINTEXT://my-cluster-kafka-bootstrap:9092

Step 2: Install bitnami schema registry:

helm install schema-registry oci://registry-1.docker.io/bitnamicharts/schema-registry -f schema-registry-values.yml --namespace kafka

Step 3: Check schema registry started

kubectl logs kafka-schema-registry-0 schema-registry -n kafka

[2023-08-19 09:06:38,783] INFO HV000001: Hibernate Validator 6.1.7.Final (org.hibernate.validator.internal.util.Version:21)
[2023-08-19 09:06:39,019] INFO Started o.e.j.s.ServletContextHandler@7e94d093{/,null,AVAILABLE} (org.eclipse.jetty.server.handler.ContextHandler:921)
[2023-08-19 09:06:39,029] INFO Started o.e.j.s.ServletContextHandler@270b6b5e{/ws,null,AVAILABLE} (org.eclipse.jetty.server.handler.ContextHandler:921)
[2023-08-19 09:06:39,040] INFO Started NetworkTrafficServerConnector@660acfb{HTTP/1.1, (http/1.1, h2c)}{0.0.0.0:8081} (org.eclipse.jetty.server.AbstractConnector:333)
[2023-08-19 09:06:39,041] INFO Started @6514ms (org.eclipse.jetty.server.Server:415)
[2023-08-19 09:06:39,041] INFO Schema Registry version: 7.4.1 commitId: 8969f9f38b043ca55d4e97536b6bcb5ccc54f42f (io.confluent.kafka.schemaregistry.rest.SchemaRegistryMain:47)
[2023-08-19 09:06:39,042] INFO Server started, listening for requests... (io.confluent.kafka.schemaregistry.rest.SchemaRegistryMain:49)

Testing Schema Registy

Once the cluster is running, you can run a producer and a consumer using Avro messages stored in Schema Registry.

Note:

Kafka consumer and producers docker images used for testing ca be found in kafka-python-client repository. This docker image contain source code of one of the examples in [confluent-kafka-python repository]https://github.com/confluentinc/confluent-kafka-python/.

Step 1: launch producer

kubectl -n kafka run kafka-producer -ti --image=ricsanfre/kafka-python-client:latest --rm=true --restart=Never -- python avro_producer.py -b my-cluster-kafka-bootstrap:9092 -s http://kafka-schema-registry:8081 -t my-avro-topic

Enter required fields for building the message

Step 3: in a different terminal launch consumer

kubectl -n kafka run kafka-consumer -ti --image=ricsanfre/kafka-python-client:latest --rm=true --restart=Never -- python avro_consumer.py -b my-cluster-kafka-bootstrap:9092 -s http://kafka-schema-registry:8081 -t my-avro-topic

Kafka UI (Kafdrop)

Kafdrop is a web UI for viewing Kafka topics and browsing consumer groups. The tool displays information such as brokers, topics, partitions, consumers, and lets you view messages.

Note:

Even when helm chart source code is available in the repository, this helm chart is not hosted in any official helm repository. I have decided to selfhost this helm chart within my own repository https://ricsanfre.github.io/helm-charts/

Step 1: Add the Helm repository:

helm repo add ricsanfre https://ricsanfre.github.io/helm-charts/

Step 2: Fetch the latest charts from the repository:
```
helm repo update
```

Step 3: Prepare kafdrop-values.yml

# Kafka broker connection
kafka:
  brokerConnect: my-cluster-kafka-bootstrap:9092ç
# JVM options
jvm:
  opts: "-Xms32M -Xmx64M"

# Adding connection to schema registry
cmdArgs: "--schemaregistry.connect=http://kafka-schema-registry:8081"

# Ingress resource
ingress:
  enabled: true
  ## Add ingressClassName to the Ingress
  ingressClassName: nginx
  # ingress host
  hosts:
    - kafdrop.picluster.ricsanfre.com
  ## TLS Secret Name
  tls:
    - secretName: kafdrop-tls
      hosts:
        - kafdrop.picluster.ricsanfre.com
  ## Default ingress path
  path: /
  ## Ingress annotations
  annotations:
    # Enable cert-manager to create automatically the SSL certificate and store in Secret
    # Possible Cluster-Issuer values:
    #   * 'letsencrypt-issuer' (valid TLS certificate using IONOS API)
    #   * 'ca-issuer' (CA-signed certificate, not valid)
    cert-manager.io/cluster-issuer: letsencrypt-issuer
    cert-manager.io/common-name: kafdrop.picluster.ricsanfre.com

# Kafdrop docker images are not multi-arch. Only amd64 image is available
affinity:
  nodeAffinity:
    requiredDuringSchedulingIgnoredDuringExecution:
      nodeSelectorTerms:
      - matchExpressions:
        - key: kubernetes.io/arch
          operator: In
          values:
          - amd64

Kafdrop is configured to use Schema Registry, so messages can be decoded when Schema Registry is used. See helm chart value cmdArgs:

--schemaregistry.connect=http://kafka-schema-registry:8081

Step 4: Install Kafdrop helm chart

helm upgrade -i kafdrop ricsanfre/kafdrop -f kafdrop-values.yml --namespace kafka

Step 4: Confirm that the deployment succeeded, opening UI:

https://kafdrop.picluster.ricsanfre.com/

References

Last Update: Sep 16, 2023

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