Strimzi Stretch Cluster - LoadBalancer Networking Provider

LoadBalancer-based networking provider plugin for Strimzi Kafka stretch clusters deployed across multiple Kubernetes clusters.

What This Plugin Does

This plugin enables cross-cluster Kafka communication by:

1. Creating LoadBalancer Services - Creates a dedicated LoadBalancer service for each Kafka broker pod
2. Waiting for IP Assignment - Waits for cloud provider to assign external IP/hostname (with exponential backoff retry, up to 5 minutes)
3. Discovering Endpoints - Extracts the assigned LoadBalancer IP/hostname and port
4. Generating Configurations - Automatically generates advertised.listeners and controller.quorum.voters configurations for Kafka brokers

Example Output:

• Service: my-cluster-kafka-0-lb with external IP 10.21.50.10
• Advertised Listener: REPLICATION-9091://10.21.50.10:9091
• Controller Quorum Voter: 0@10.21.50.10:9091

How It Works

1. Service Creation

For each broker pod, the plugin creates a LoadBalancer service:

apiVersion: v1
kind: Service
metadata:
  name: my-cluster-kafka-0-lb
spec:
  type: LoadBalancer
  selector:
    statefulset.kubernetes.io/pod-name: my-cluster-kafka-0
  ports:
  - name: tcp-replication
    port: 9091
  - name: tcp-plain
    port: 9092

2. IP Assignment Wait

The plugin waits for the cloud provider/LoadBalancer controller to assign an external IP:

• Retry Logic: Exponential backoff (10s → 20s → 30s...)
• Maximum Wait: 5 minutes per broker
• Cloud Provider Dependent: AWS ELB/NLB, GCP LB, Azure LB, MetalLB, etc.

3. Endpoint Discovery

Once the IP is assigned, the plugin extracts it from service.status.loadBalancer.ingress[0]:

• IP address: 10.21.50.10
• Or hostname: a1b2c3-123.us-west-2.elb.amazonaws.com

Prerequisites

LoadBalancer Support Required:

• Cloud: AWS ELB/NLB, GCP Load Balancer, Azure Load Balancer
• On-Premises: MetalLB, Cilium BGP, or similar LoadBalancer controller
• Network: Connectivity between all cluster LoadBalancer IPs

Building the Plugin

Quick Build (Recommended)

Use the automated build script:

./build-plugin.sh

This script will:

1. Build and install Strimzi cluster-operator to local Maven repository
2. Build the LoadBalancer plugin JAR
3. Verify the JAR contents
4. Show next deployment steps

Manual Build

If you prefer to build manually:

# First, build and install the Strimzi cluster-operator
cd ../strimzi-kafka-operator
mvn clean install -pl cluster-operator -am -DskipTests -Dcheckstyle.skip=true

# Then build the plugin
cd ../strimzi-stretch-loadbalancer-plugin
mvn clean package

This produces: target/strimzi-stretch-loadbalancer-plugin-0.48.0.jar

Deploying the Plugin

1. Add JAR to Operator

Mount the plugin JAR into the Strimzi operator:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: strimzi-cluster-operator
spec:
  template:
    spec:
      containers:
      - name: strimzi-cluster-operator
        volumeMounts:
        - name: stretch-plugins
          mountPath: /opt/strimzi/plugins
      volumes:
      - name: stretch-plugins
        hostPath:
          path: /opt/strimzi/plugins  # Copy JAR here on operator node

2. Configure Operator Environment Variables

Enable the plugin by setting these environment variables in the operator deployment:

env:
- name: STRIMZI_STRETCH_PLUGIN_CLASS_NAME
  value: io.strimzi.plugin.stretch.LoadBalancerNetworkingProvider
- name: STRIMZI_STRETCH_PLUGIN_CLASS_PATH
  value: /opt/strimzi/plugins/*

Network Requirements

LoadBalancer Controller:

• Ensure LoadBalancer controller is running (cloud provider controller or MetalLB)
• Configure appropriate IP address pools

For MetalLB (on-premises example):

apiVersion: metallb.io/v1beta1
kind: IPAddressPool
metadata:
  name: kafka-pool
  namespace: metallb-system
spec:
  addresses:
  - 10.21.50.10-10.21.50.50

Firewall:

• Allow traffic on Kafka ports (9090, 9091, 9092, etc.)
• LoadBalancer IPs must be routable between clusters

Troubleshooting

LoadBalancer IP Not Assigned

Symptom: Timeout after ~5 minutes waiting for LoadBalancer IP

Solutions:

• Check cloud provider LoadBalancer quota/limits
• Verify LoadBalancer controller is running: kubectl get pods -n metallb-system (for MetalLB)
• Check service events: kubectl describe svc my-cluster-kafka-0-lb
• Verify IPAddressPool configuration (for MetalLB)

Slow Reconciliation

This is normal. LoadBalancer IP assignment can take 2-5 minutes per broker depending on the cloud provider. The plugin uses exponential backoff and waits up to 5 minutes per broker.

License

Apache License 2.0

Version

• Plugin Version: 0.48.0
• Compatible with: Strimzi 0.48.0+
• Requires: Kubernetes 1.25+ with LoadBalancer support