Creating and Configuring an Encrypted GemFire Client in Java

Louis Jacome February 8, 2023


VMware GemFire for Kubernetes is a Kubernetes Operator-patterned solution that utilizes the Kubernetes platform to help you quickly and reliably deploy robust GemFire clusters. GemFire is a distributed, in-memory, key-value store that performs read and write operations at amazingly fast speeds. It offers highly available parallel message queues, continuous availability, and an event-driven architecture you can scale dynamically, with no downtime. This means as your requirements increase to support more data, high-performance, real-time apps, GemFire can scale linearly with ease.

This tutorial explores how to develop and deploy a basic GemFire client that performs distributed caching operations with a TLS-secured GemFire for Kubernetes cluster. We will touch on Maven and TLS configuration of the Java-based client, configuring the GemFire cluster, using cert-manager to create resources for the client, and deploying the client application to Kubernetes. cert-manager is a cloud native X.509 certificate management for Kubernetes and OpenShift.

The reader is expected to have some exposure to GemFire and some development experience with Java and Kubernetes. If you would like to learn more about GemFire and all of it capabilities please head over to: VMware GemFire

The code for the GemFire client and Kubernetes resource definitions used in this tutorial are available on github.

Creating a GemFire Client in Java

To start, we’ll build a basic GemFire client in Java. The focus here will be on creating a client that has the minimal configuration necessary to do put and get operations against an already running GemFire cluster. As such, this post will make use of the available GemFire API methods for clients.

Maven Configuration

The Maven configuration includes all the necessary plugins to compile and distribute the client along with the GemFire dependency. In this example maven-compiler-plugin builds the GemFire client using Java 8, while the maven-assembly-plugin is used to create a single executable jar. The current version of GemFire 9.15 is also compatible with JDK 8, JDK 11 and JDK 17.

The entry point for the maven-compiler-plugin is specified by the mainClass tag which is the fully qualified name of the client application com.vmware.gemfire.BasicGemFireClient.


        <name>Pivotal GemFire Release Repository</name>

To access these dependencies, you must add an entry with valid credentials to the GemFire Release Repository to your .m2/settings.xml file, as shown below. For more details see Obtaining VMware GemFire from a Maven Repository

            <username>[email protected]</username>

To build the executable jar with dependencies included, run:

mvn clean compile assembly:single

That command places the jar in the auto-generated target directory.

Writing the BasicGemFireClient

GemFire is a key-value database and a given GemFire cluster can have many key-value stores. GemFire calls these key-value stores “Region” after a region of memory. From an implementation perspective Region extends a java.util.concurrent.ConcurrentMap, which is familiar to Java developers that know and use Java Maps. As a result, learning how to program with GemFire is straight forward. GemFire supports a rich feature that goes beyond the scope of this blog. For more information on how to use a region see Data Regions in the GemFire documentation for details.

Let’s walk through some of the code in our example client application. For simplicity, the BasicGemFireClient is a single class with methods that perform data operations. The BasicGemFireClient has a constructor that accepts a region instance to perform operations on. The region uses generics of <Integer, String> to avoid casting any results. As noted above, GemFire Regions extend standard Java Maps, this region then is a Java Map of integers to strings. Constructor:

public class BasicGemFireClient {
 private final Region<Integer, String> region;
 public BasicGemFireClient(Region<Integer, String> region) {
   this.region = region;

BasicGemFireClient.putData() generates the region data in a for loop. We will use the ordinal as the key and concatenate that ordinal with the string value to create our value. Then we store the Integer key and the concatenated String value using the put method.

 void putData(int numValues) {
   for(int i = 0; i < numValues; i++) {
     region.put(i, "value" + i);

BasicGemFireClient.getRegionKeys() gets the set of keys on the server. If we asked the client region for it’s key set it could vary based on the policy set on the client region. As one gets more advanced GemFire architectures it will make sense for this design choice. For this application we just care about all the keys on the server, not what is stored on the client. The client will ask the server(s) for its key set.

 Set<Integer> getRegionKeys() {
   return new HashSet<>(region.keySetOnServer());

BasicGemFireClient.getAndPrintValues() this method iterates through the set of keys and asks the server for each value associated with a given key with the Region.get method. It then prints that key and the corresponding value out.

 void getAndPrintValues(Set<Integer> keySet) {
   for(Integer key : values) {
     System.out.printf("%d:%s\n", key, region.get(key));

Configuring the BasicGemFireClient

As we saw, to instantiate the BasicGemFireClient a region must be provided. There are several GemFire region types to choose from based on high availability, asynchronous distributions, query performance, and more. For a GemFire client though, we have three region options to consider: local, proxy, and caching proxy.

  • LOCAL - region is only accessible to the process on which it was started, data and operations are not distributed to other members. This type of region would be good for any application meta data that is needed. The easiest way to think about a local region is maybe GemFire is embedded in a desktop application. Local regions can persist data and can even be queried.
  • CACHING_PROXY - regions use some of the client application memory space to cache some of the data held on the server.
  • PROXY - regions hold no state information, and simply forwards data and cache operations to the regions held on the server. Proxy regions are the simplest to get started with. I recommend just making proxy regions until you find empirical evidence that your application needs more.

The BasicGemFireClient was designed to be run in the same Kubernetes cluster where the GemFire cluster and operator are deployed. Since we recommend Proxy client regions our code will instantiate our client region as a proxy region.

By default, a GemFire for Kubernetes cluster is secured by TLS, which requires that the client to be properly configured to connect. For our example client, the configuration will consist of the location of both keystore and truststore along with their passwords; see Configuring SSL for more details. The client can then use the GemFire API to create a cache reference after providing the configured SSL properties.

There are many ways to handle secrets in Kubernetes, since this is a learning experiance we are going doing it as easy as possible. For this example we are going to pass configuration parameters as environment variables which can be declared in the application’s corresponding Pod spec/yaml. For the BasicGemFireClient, the hostnames for the GemFire cluster, truststore, and keystore passwords are consumed as environment variables; specifically TRUST_PSWD is used as both the truststore and keystore password (for convenience) and is set by reading the value of the TRUST_STORE_PSWD environment variable. The host for the GemFire cluster is set by reading the value of the LOCATOR_HOST environment variable. The location of the truststore and keystore files are hard-coded to the expected location on disk – within the */certs* directory.

Setting up the GemFire TLS Connection:

String locatorAddress = System.getenv("LOCATOR_HOST");
String TRUST_PSWD= System.getenv("TRUST_STORE_PSWD");
Properties props = new Properties();
props.setProperty("ssl-enabled-components", "all");
props.setProperty("ssl-endpoint-identification-enabled", "true");
props.setProperty("ssl-keystore", "/certs/keystore.p12");
props.setProperty("ssl-keystore-password", TRUST_PSWD);
props.setProperty("ssl-truststore", "/certs/truststore.p12");
props.setProperty("ssl-truststore-password", TRUST_PSWD);
// connect to the locator using default port 10334
ClientCache cache = new ClientCacheFactory(props)
   .addPoolLocator(locatorAddress, 10334);

The ClientCache is an interface that GemFire clients use to manage data. From this ClientCache we can then create client regions based on whatever policy your architects need. As recommended our example client application region will be a proxy for the real cache in the running GemFire cluster.

Region<Integer, String> region =
   cache.<Integer, String>createClientRegionFactory(ClientRegionShortcut.PROXY)

Note: Before clients can use this example-region proxy region the example-region region must be created on the servers. This will be shown in a later step using the GemFire CLI called gfsh (pronounced gee-FISH)

Running the BasicGemFireClient

With the configuration ready, all that’s left to do is instantiate the BasicGemFireClient and execute the available data operations.

BasicGemFireClient example = new BasicGemFireClient(region);

A successful run of the client will put 10 key-value pairs into the region, and get the values before and displaying the results:


Creating a BasicGemFireClient Docker container image

To run the client application in Kubernetes, a container image must be built and uploaded to a container registry. Provided in the example git repository is a Dockerfile that builds the BasicGemFireClient container image. To build the image, from the root of the git repository execute

docker build --tag <<IMAGE-REPOSITORY>>/gfclient .
docker push <<IMAGE-REPOSITORY>>/gfclient

This will build then push the container image to the image repository substituted in place of <<IMAGE-REPOSITORY>>.

Preparing the GemFire for Kubernetes cluster

Installing GemFire for Kubernetes and Creating a GemFire cluster

To date, GemFire for Kubernetes has been certified on the following platforms: Azure Kubernetes Service, Amazon Elastic Kubernetes Service, Google Kubernetes Engine, Red Hat OpenShift, Tanzu Kubernetes Grid, and Tanzu Kubernetes Grid Integrated Edition.

To install GemFire for Kubernetes on one of the above platforms, please consult the Prerequisites and Supported Platforms and Install or Uninstall the Tanzu GemFire Operator product pages.

A sample (1 locator, 2 server) GemFire for Kubernetes cluster yaml is provided below to run alongside the BasicGemFireClient application. Note, the vmware-gemfire container image, run by GemFire member pods, must be available at the desired image repository substituted in for <<IMAGE-REPOSITORY>>.


kind: GemFireCluster
 name: gemfire-cluster
 antiAffinityPolicy: Cluster
   replicas: 1
       memory: 1Gi
       cpu: "1"
       memory: 1Gi
       cpu: "1"
         storage: "1Gi"
   replicas: 2
       memory: 2Gi
       cpu: "2"
       memory: 2Gi
       cpu: "2"
         storage: "10Gi"

To create the GemFire for Kubernetes cluster, execute

kubectl apply -f gemfirecluster.yaml

Once the above GemFire cluster is up and running, lets create the example-region region for the client application. The process below shows how to create the region by shelling into a locator pod, launching gfsh, and executing the create region command:

Shell into the locator pod using kubectl

kubectl exec -it gemfire-cluster-locator-0 sh

Within the locator shell, retrieve the fully qualified domain name of the locator (FQDN), then launch gfsh

$ hostname -f
$ gfsh

From gfsh, connect to the GemFire cluster specifying the locator’s FQDN with the default locator port 10334, and security properties file with TLS configuration. Proceed past the prompts by pressing enter and proceed to connect to the GemFire cluster.

gfsh>connect --locator=<<LOCATOR-FQDN>>[10334] --security-properties-file=/security/

Once connected, create the example-region

gfsh>create region --name='example-region' --type=PARTITION

Now the GemFire cluster is configured and ready for the BasicGemFireClient application.

Creating cert-manager Resources for the BasicGemFireClient

In this section, several yaml files will be provided that define necessary Kubernetes resources to run the BasicGemFireClient application. It’s assumed that the kubectl is targeting the intended Kubernetes cluster.

Commands to ensure we are using the right Kubernetes cluster:

# List available Kubernetes clusters
kubectl config get-contexts
# Currently targeted cluster
kubectl config current-context
# Change targeted cluster to 'my-kubernetes-cluster-name'
kubectl config use-context my-kubernetes-cluster-name

cert-manager is a prerequisite of GemFire for Kubernetes. It greatly simplifies the process of generating and managing certificates in Kubernetes. In the configuration of the BasicGemFireClient application, it’s required that truststore and keystore files be on the client filesystem to connect to the GemFire for Kubernetes cluster. After taking advantage of the certificate issuer bundled with the GemFire for Kubernetes operator, generating these files is simplified to a three step process:

  1. Create a Kubernetes secret that stores the certificate data
  2. Create a Certificate to generate the certificate data
  3. Mount the Secret to a volume in the BasicGemFireClient Pod

Create the Secret

First, generate a Secret that will be used to store the certificate data after cert-manager generates it. cert-secret.yaml below defines a Secret named client-cert in the app namespace. The provided password (“client-password”) is used to secure the truststore and keystore files.


apiVersion: v1
kind: Secret
 name: client-cert
 namespace: app
 password: client-password

To create the Secret, execute

kubectl apply -f cert-secret.yaml

Create the Certificate

Next, generate the Certificate using cert-manager.

client-cert.yaml defines a Certificate that will be issued by the gemfire-ca-issuer. This issuer is bundled with the GemFire for Kubernetes operator. Other important fields include dnsNames (Subject Alternative Names) which associate various objects in the app namespace with the certificate, the secretName is where cert-manager stores the certificate data, keystores generates a keystore in the GemFire-supported pkcs12 format using the password provided in the client-cert Secret.


kind: Certificate
 name: client-cert
 namespace: app
 duration: 2160h # 90d
 renewBefore: 360h # 15d
 commonName: client-cert
 isCA: false
   algorithm: RSA
   encoding: PKCS1
   size: 2048
 - server auth
 - client auth
 - "*.app"
   kind: ClusterIssuer
   name: gemfire-ca-issuer
 secretName: client-cert
     create: true
       key: password
       name: client-cert

Create the Certificate by executing

kubectl apply -f client-cert.yaml

Once complete, the certificate data is stored in the client-cert Secret created earlier.

Note: If the default configuration for TLS mutual/two-way authentication is desired, the truststore will be used by the client to authenticate the server’s provided certificate. This is enabled by setting clientAuthenticationRequired to true in the tls section of the gemfirecluster.yaml.

kind: GemFireCluster
      clientAuthenticationRequired: true

Mount the Secret to a volume in the BasicGemFireClient Pod

Finally, define the Pod for the BasicGemFireClient application. The Pod will deploy to the app namespace and use the gfclient Docker container image created earlier after substituting the desired image repository in place of<<IMAGE-REPOSITORY>>.


apiVersion: v1
kind: Pod
 name: gfclient
 namespace: app
 - name: gfclient
   image: <<IMAGE-REPOSITORY>>/gfclient:latest
   imagePullPolicy: Always
   - mountPath: /certs
     name: cert-volume
   - name: "TRUST_STORE_PSWD"
         name: client-cert
         key: password
   - name: "LOCATOR_HOST"
     value: "<<LOCATOR-FQDN or IP-ADDRESS>>"
 - name: cert-volume
     secretName: client-cert

The certificate contents of cert-secret will be on the Pod filesystem under /certs. In addition, the required values for the environment variable TRUST_STORE_PSWD is retrieved from the client-cert secret while the LOCATOR_HOST value is hard-coded to either the FQDN of a locator in the GemFire cluster or its IP address.

To create the BasicGemFireClient Pod, execute

kubectl apply -f gfclient.yaml

Once created, the Pod starts the BasicGemFireClient application created above. After successfully running, one can inspect the Pod logs and see the expected output:

kubectl logs gfclient -n app
# Attempting connection to locator gemfire-cluster-locator.default.svc.cluster.local
# ERROR StatusLogger Log4j2 could not find a logging implementation. Please add log4j-core to the classpath. Using #SimpleLogger to log to the console...
# SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
# SLF4J: Defaulting to no-operation (NOP) logger implementation
# SLF4J: See for further details.
# 0:value0
# 1:value1
# 2:value2
# 3:value3
# 4:value4
# 5:value5
# 6:value6
# 7:value7
# 8:value8
# 9:value9

This concludes the tutorial, we have covered how to:

  • Develop a GemFire client (using Java & maven) capable of doing distributed caching operations
  • Configure the client to communicate with a TLS-enabled GemFire cluster
  • Containerize the client application
  • Install VMware GemFire for Kubernetes and create a GemFire cluster
  • Create cert-manager resources for the GemFire client
  • Deploy the GemFire client