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Kubernetes Discovery for Hazelcast
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Hazelcast Discovery Plugin for Kubernetes

This repository contains a plugin which provides the automatic Hazelcast member discovery in the Kubernetes environment.

You can use it in your project deployed on Kubernetes in order to make the embedded Hazelcast members discover each other automatically. This plugin is also included in Hazelcast Docker images, Hazelcast Helm Charts, and Hazelcast OpenShift Docker image.

Requirements and Recommendations

  • Your Java Runtime Environment must support TLS 1.2 (which is the case for most modern JREs).
  • Versions compatibility: hazelcast-kubernetes 1.3+ is compatible with hazelcast 3.11+; for older hazelcast versions you need to use hazelcast-kubernetes 1.2.x.
  • The recommendation is to use StatefulSet for managing Hazelcast PODs; in case of using Deployment (or ReplicationController), the Hazelcast cluster may start with Split Brain (which will anyway re-form to one consistent cluster in a few minutes).

Embedded mode

To use Hazelcast embedded in your application, you need to add the plugin dependency into your Maven/Gradle file. Then, when you provide hazelcast.yaml as presented below or an equivalent Java-based configuration, your Hazelcast instances discover themselves automatically.




compile group: "com.hazelcast", name: "hazelcast-kubernetes", version: "${hazelcast-kubernetes-version}"

Understanding Discovery Modes

The following table summarizes the differences between the discovery modes: Kubernetes API and DNS Lookup.

Kubernetes API DNS Lookup
Description Uses REST calls to Kubernetes Master to fetch IPs of PODs Uses DNS to resolve IPs of PODs related to the given service
Pros Flexible, supports 3 different options:
- Hazelcast cluster per service
- Hazelcast cluster per multiple services (distinguished by labels)
- Hazelcast cluster per namespace
No additional configuration required, resolving DNS does not require granting any permissions
Cons Requires setting up RoleBinding (to allow access to Kubernetes API) - Limited to headless Cluster IP service
- Limited to Hazelcast cluster per service


This plugin supports two different options of how Hazelcast members discover each others:

  • Kubernetes API
  • DNS Lookup

Kubernetes API

Kubernetes API mode means that each node makes a REST call to Kubernetes Master in order to discover IPs of PODs (with Hazelcast members).

Granting Permissions to use Kubernetes API

Using Kubernetes API requires granting certain permissions. Therefore, you may need to create rbac.yaml with the following content.

kind: ClusterRoleBinding
  name: default-cluster
  kind: ClusterRole
  name: view
- kind: ServiceAccount
  name: default
  namespace: default

Then, apply rbac.yaml.

$ kubectl apply -f rbac.yaml

Note: You can be even more strict with the permissions and create your own Role. For details, please check the implementation of Hazelcast Helm Chart.

Creating Service

Hazelcast Kubernetes Discovery requires creating a service to PODs where Hazelcast is running. In case of using Kubernetes API mode, the service can be of any type.

kind: Service
  type: LoadBalancer
    app: APP-NAME
  - name: hazelcast
    port: 5701

Hazelcast Configuration

The second step is to configure the discovery plugin inside hazelcast.yaml or an equivalent Java-based configuration.

        enabled: false
        enabled: true
        namespace: MY-KUBERNETES-NAMESPACE
        service-name: MY-SERVICE-NAME
      .setProperty("namespace", "MY-KUBERNETES-NAMESPACE")
      .setProperty("service-name", "MY-SERVICE-NAME");

There are several properties to configure the plugin, all of them are optional.

  • namespace: Kubernetes Namespace where Hazelcast is running; if not specified, the value is taken from the environment variables KUBERNETES_NAMESPACE or OPENSHIFT_BUILD_NAMESPACE
  • service-name: service name used to scan only PODs connected to the given service; if not specified, then all PODs in the namespace are checked
  • service-label-name, service-label-value: service label and value used to tag services that should form the Hazelcast cluster together
  • pod-label-name, pod-label-value: pod label and value used to tag pods that should form the Hazelcast cluster together.
  • resolve-not-ready-addresses: if set to true, it checks also the addresses of PODs which are not ready; false by default
  • use-node-name-as-external-address: if set to true, uses the node name to connect to a NodePort service instead of looking up the external IP using the API; false by default
  • kubernetes-api-retries: number of retries in case of issues while connecting to Kubernetes API; defaults to 3
  • kubernetes-master: URL of Kubernetes Master; https://kubernetes.default.svc by default
  • api-token: API Token to Kubernetes API; if not specified, the value is taken from the file /var/run/secrets/
  • ca-certificate: CA Certificate for Kubernetes API; if not specified, the value is taken from the file /var/run/secrets/
  • service-port: endpoint port of the service; if specified with a value greater than 0, it overrides the default; 0 by default

You can use one of service-name,service-label(service-label-name,service-label-value) and pod-label(pod-label-name, pod-label-value) based discovery mechanisms, configuring two of them at once does not make sense.

Note: If you don't specify any property at all, then the Hazelcast cluster is formed using all PODs in your current namespace. In other words, you can look at the properties as a grouping feature if you want to have multiple Hazelcast clusters in one namespace.

DNS Lookup

DNS Lookup mode uses a feature of Kubernetes that headless (without cluster IP) services are assigned a DNS record which resolves to the set of IPs of related PODs.

Creating Headless Service

Headless service is a service of type ClusterIP with the clusterIP property set to None.

kind: Service
  type: ClusterIP
  clusterIP: None
    app: APP-NAME
  - name: hazelcast
    port: 5701

Hazelcast Configuration

The Hazelcast configuration to use DNS Lookup looks as follows.

        enabled: false
        enabled: true
        service-dns: MY-SERVICE-DNS-NAME
      .setProperty("service-dns", "MY-SERVICE-DNS-NAME");

There are 2 properties to configure the plugin:

  • service-dns (required): service DNS, usually in the form of SERVICE-NAME.NAMESPACE.svc.cluster.local
  • service-dns-timeout (optional): custom time for how long the DNS Lookup is checked

Note: In this README, only YAML configurations are presented, however you can achieve exactly the same effect using XML or Java-based configurations.

Zone Aware

When using ZONE_AWARE configuration, backups are created in the other availability zone. This feature is available only for the Kubernetes API mode.

Note: Your Kubernetes cluster must orchestrate Hazelcast Member PODs equally between the availability zones, otherwise Zone Aware feature may not work correctly.

YAML Configuration

  enabled: true
  group-type: ZONE_AWARE

Java-based Configuration


Note the following aspects of ZONE_AWARE:

  • Kubernetes cluster must provide the well-known Kubernetes annotations
  • Retrieving Zone Name uses Kubernetes API, so RBAC must be configured as described here
  • ZONE_AWARE feature works correctly when Hazelcast members are distributed equally in all zones, so your Kubernetes cluster must orchestrate PODs equally

Note also that retrieving Zone Name assumes that your container's hostname is the same as POD Name, which is almost always true. If you happen to change your hostname in the container, then please define the following environment variable:

 - name: POD_NAME

Hazelcast Client Configuration

Depending on whether your Hazelcast Client runs inside or outside the Kubernetes cluster, its configuration looks different.

Inside Kubernetes Cluster

If you have a Hazelcast cluster deployed on Kubernetes and you want to configure Hazelcast Client deployed on the same Kubernetes cluster, then the configuration looks very similar to Hazelcast Member.

Here's an example in case of the Kubernetes API mode.

      enabled: true
      service-name: MY-SERVICE-NAME
            .setProperty("namespace", "MY-KUBERNETES-NAMESPACE")
            .setProperty("service-name", "MY-SERVICE-NAME");

Outside Kubernetes Cluster

If your Hazelcast cluster is deployed on Kubernetes, but Hazelcast Client is in a completely different network, then they can connect only through the public Internet network.

To use Hazelcast Dummy Client (<smart-routing>false</smart-routing>) you don't need any plugin, it's enough to expose your Hazelcast cluster with a LoadBalancer (or NodePort) service and set its IP/port as the TCP/IP Hazelcast Client configuration. Dummy Client, however, compromises the performance, since all the communication happens against a single Hazelcast member.

To configure Hazelcast Smart Client, you need to perform the following steps:

  • Expose each Hazelcast Member POD with a separate LoadBalancer or NodePort service (the simplest way to do it is to install Metacontroller and service-per-pod Decorator Controller)
  • Configure ServiceAccount with ClusterRole having at least get and list permissions to the following resources: endpoints, pods, nodes, services
  • Use credentials from the created ServiceAccount in the Hazelcast Client configuration (credentials can be fetched with kubectl get secret <sevice-account-secret> -o jsonpath={.data.token} | base64 --decode and kubectl get secret <sevice-account-secret> -o jsonpath={\\.crt} | base64 --decode)
      enabled: true
      service-name: MY-SERVICE-NAME
      use-public-ip: true
      api-token: eyJhbGciOiJSUzI1NiIsImtpZCI6IiJ9.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.o-j4e-ducrMmQc23xYDnPr6TIyzlAs3pLNAmGLqPe9Vq1mwsxOh3ujcVKR90HAdkfHIF_Sw66qC9hXIDvxfqN_rLXlOKbvTX3gjDrAnyY_93Y3MpmSBj8yR9yHMb4O29a9UIwN5F2_VoCsc0IGumScU_EhPYc9mvEXlwp2bATQOEU-SVAGYPqvVPs9h5wjWZ7WUQa_-RBLMF6KRc9EP2i3c7dPSRVL9ZQ6k6OyUUOVEaPa1tqIxP7vOgx9Tg2C1KmYF5RDrlzrWkhEcjd4BLTiYDKEyaoBff9RqdPYlPwu0YcEH-F7yU8tTDN74KX5jvah3amg_zTiXeNoe5ZFcVdg
      ca-certificate: |
        -----BEGIN CERTIFICATE-----
        -----END CERTIFICATE-----

Note: Hazelcast Client outside Kubernetes cluster works only in the Kubernetes API mode (it does not work in the DNS Lookup mode).

Rolling Upgrade and Scaling

Hazelcast cluster is easily scalable within Kubernetes. You can use the standard kubectl scale command to change the cluster size. The same applies the rolling upgrade procedure, you can depend on the standard Kubernetes behavior and just update the new version to your Deployment/StatefulSet configurations.

Note however that, by default, Hazelcast does not shutdown gracefully. It means that if you suddenly terminate more than your backup-count property (1 by default), you may lose the cluster data. To prevent that from happening, set the following properties:

  • terminationGracePeriodSeconds: in your StatefulSet (or Deployment) configuration; the value should be high enough to cover the data migration process
  • -Dhazelcast.shutdownhook.policy=GRACEFUL: in the JVM parameters
  • -Dhazelcast.graceful.shutdown.max.wait: in the JVM parameters; the value should be high enough to cover the data migration process


  • If you use Deployment (not StatefulSet), you need to set your strategy to RollingUpdate and ensure Pods are updated one by one.
  • If you upgrade by the minor version, e.g., 3.11.4 => 3.12 (Enterprise feature), you need to set the following JVM property to make sure the cluster version updates automatically.

All these features are already included in Hazelcast Helm Charts.

Plugin Usages

Apart from embedding Hazelcast in your application as described above, there are multiple other scenarios of how to use the Hazelcast Kubernetes plugin.

Docker images

This plugin is included in the official Hazelcast Docker images:

Please check Hazelcast Kubernetes Code Samples for the their usage.

Helm Chart

Hazelcast is available in the form of Helm Chart in a few versions:

You can also check Hazelcast Helm Charts at Helm Hub.

Kubernetes/OpenShift Operator

Hazelcast is available as Kubernetes/OpenShift Operator:

Red Hat OpenShift

The plugin is used to provide the OpenShift integration, please check Hazelcast OpenShift Code Samples for details.


Hazelcast works correctly with Istio >= 1.1.0 without any need of additional configuration. You can use it in both client-server and embedded modes. Also, the Hazelcast cluster can be either outside or inside the Istio mesh.

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