It's possible to embed multiple Hazelcast instances into an application deployed in a single POD. Then, you can control how the cluster are formed. It requires an additional configuration, but you don't have to modify HazelcastKubernetesDiscoveryStrategy.

Sample application

I've created a sample application to present how it works. Please check it here: https://github.com/leszko/hazelcast-code-samples/tree/kubernetes-embedded-multiple/hazelcast-integration/kubernetes/samples/embedded.

Configuration steps

Hazelcast Configuration

You have two Hazelcast instances in your application, so you need to specify the ports they use. Also, with the parameters of the hazelcast-kubernetes plugin, you can configure which Hazelcast instances form the cluster together.

For example, assuming the first Hazelcast instance should form a cluster with all other Hazelcast instances in the current Kubernetes namespace, its configuration can look as follows.

Config config = new Config();config.getNetworkConfig().setPort(5701);config.getProperties().setProperty("hazelcast.discovery.enabled", "true");JoinConfig joinConfig = config.getNetworkConfig().getJoin();joinConfig.getMulticastConfig().setEnabled(false);HazelcastKubernetesDiscoveryStrategyFactory discoveryStrategyFactory = new HazelcastKubernetesDiscoveryStrategyFactory();Map<String, Comparable> properties = new HashMap<>();joinConfig.getDiscoveryConfig().addDiscoveryStrategyConfig(new DiscoveryStrategyConfig(discoveryStrategyFactory, properties));

Then, the second Hazelcast instance could form the cluster only with the same application. We could make this separation by giving it a service-name parameter with the value from environment variables.

Config config = new Config();config.getNetworkConfig().setPort(5702);config.getProperties().setProperty("hazelcast.discovery.enabled", "true");JoinConfig joinConfig = config.getNetworkConfig().getJoin();joinConfig.getMulticastConfig().setEnabled(false);HazelcastKubernetesDiscoveryStrategyFactory discoveryStrategyFactory = new HazelcastKubernetesDiscoveryStrategyFactory();Map<String, Comparable> properties = new HashMap<>();String serviceName = System.getenv("KUBERNETES_SERVICE_NAME");properties.put("service-name", serviceName);properties.put("service-port", "5702");joinConfig.getDiscoveryConfig().addDiscoveryStrategyConfig(new DiscoveryStrategyConfig(discoveryStrategyFactory, properties));GroupConfig groupConfig = new GroupConfig("separate");

Kubernetes Template

Then, in the Kubernetes Deployment template, you need to configure both ports: 5701 and 5702.

ports:- containerPort: 5701- containerPort: 5702

And the environment variable with the service name:

env:- name: KUBERNETES_SERVICE_NAME  value: hazelcast-separate-1

Plus, you need to create two services, for each Hazelcast instance.

kind: Servicemetadata:  name: hazelcast-shared-1spec:  type: ClusterIP  selector:    app: hazelcast-app  ports:  - name: hazelcast-shared    port: 5701kind: Servicemetadata:  name: hazelcast-separate-1spec:  type: ClusterIP  selector:    app: hazelcast-app  ports:  - name: hazelcast-separate  port: 5702

Obviously, in the same manner, you can separate Hazelcast clusters using service labels instead of service names.