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IMPORTANT: This README is relevant for the current branch/tag you have selected above.

Provides a Etcd based discovery strategy for Hazlecast 3.6+ enabled applications. This is an easy to configure plug-and-play Hazlecast DiscoveryStrategy that will optionally register each of your Hazelcast instances with Etcd and enable Hazelcast nodes to dynamically discover one another via Etcd.

Diagram of hazelcast etcd discovery strategy


This is beta code, tested against Hazelcast 3.6-EA+ through 3.6 stable

IMPORTANT:: Do not rely on JCenter/Bintray anymore! Update your gradle/maven dependencies to use Maven Central:


  • 1.0-RC4-20210205: Same as 1.0-RC4 but made compliant for Maven Central due to JCenter/Bintray closure. Includes explicit dependency of HZ [3.6,3.12]

  • 1.0-RC4: Java 1.7+. SSL cert file improvements pull/5

  • 1.0-RC3: Tested against Hazelcast 3.6-EA through 3.6 stable, add support for username and password for issue #1

  • 1.0-RC2: Tested against Hazelcast 3.6-EA through 3.6 stable

  • 1.0-RC1: Tested against Hazelcast 3.6-EA and 3.6-RC1



To use this discovery strategy in your Maven or Gradle project use the dependency samples below.


repositories {

dependencies {
	compile 'org.bitsofinfo:hazelcast-etcd-discovery-spi:1.0-RC4-20210205'




  • Supports two modes of operation:

    • Read-write: peer discovery and registration of a hazelcast instance (self registration)
    • Read-only: peer discovery only with an manual Etcd key-path setup (no registration by the strategy itself)
  • If you don't want to use the built in Etcd registration, just specify the DoNothingRegistrator (see below) in your hazelcast discovery-strategy XML config. This will require you to manually create node key-paths against Etcd that defines the hazelcast service; in the format:

    • /[etcd-service-name]/[hz-instance-id] = {"ip":"xx.xx.xx.xx", "hostname":"", "port":5701} where hz-instance-id can be anything but must be unique.
    • etcd-service-name must match the value of the <etcd-service-name> in your hazelcast XML config for this discovery strategy.
  • If using self-registration, either LocalDiscoveryNodeRegistrator or ExplicitIpPortRegistrator which additionally support:

    • Automatic registration of the hazelcast instance with Etcd (under <etcd-service-name> key)
    • Control which IP/PORT is published for the hazelcast node in Etcd
    • Configurable discovery delay
    • Automatic Etcd de-registration of instance via ShutdownHook


  • Ensure your project has the hazelcast-etcd-discovery-spi artifact dependency declared in your maven pom or gradle build file as described above. Or build the jar yourself and ensure the jar is in your project's classpath.

  • Have Etcd running and available somewhere on your network, start it such as:

  • Configure your hazelcast.xml configuration file to use the EtcdDiscoveryStrategy (similar to the below): See hazelcast-etcd-discovery-spi-example.xml for a full example with documentation of options.

  • Launch your hazelcast instances, configured with the Etcd discovery-strategy similar to the below: see example.

Secured Communication

By default, when the HTTPS protocol is defined in order to communicate with ETCD the standard SSLContext is used (usually using 'cacerts' system keystore, if not set otherwise). If you need to define your own SSLContext with custom certificates there are three optional parameters for defining input for a custom SSLContext in order to establish secure communication to ETCD.

The optional security properties provide locations of certificates (and keys) for secure communication. You can configure trusted root certificates that are needed for communication with ETCD, when secure communication is enabled for your ETCD instance. You can also provide a client certificate and a private key through 'etcd-client-cert-location' and 'etcd-client-key-location' in case your ETCD has client-authentication activated and requests a client certificate.

In case your root certificates and client certificate are chained in one file it is OK to define this file in 'etcd-client-cert-location' and omit the trusted-cert property. The implementation will extract the first certificate as your client certificate and the rest as the trusted root/intermediate certificates.

Certificates should be X509 and provided in a PEM encoded file. Keys can be provided as PKCS#8 or PKCS#1 in a PEM encoded file.

  <port auto-increment="true">5701</port>

    <multicast enabled="false"/>
    <aws enabled="false"/>
    <tcp-ip enabled="false" />

       <discovery-strategy enabled="true"

              <property name="etcd-uris">http://localhost:4001</property>
              <!-- Optional Username for etcd -->
              <property name="etcd-username">root</property>
              <!-- Optional Password for etcd -->
              <property name="etcd-password">password</property>
		       <property name="etcd-service-name">hz-discovery-test-cluster</property>
              <property name="etcd-registrator">org.bitsofinfo.hazelcast.discovery.etcd.LocalDiscoveryNodeRegistrator</property>
              <!-- Optional cert/key files for SSL connection to etcd, in case etcd is configured for secure communication -->
              <property name="etcd-client-cert-location">/path/to/tls.crt</property>
              <property name="etcd-client-key-location">/path/to/tls.key</property>
              <property name="etcd-trusted-cert-location">/path/to/trusted.crt</property>
		       <property name="etcd-registrator-config"><![CDATA[

  • Once nodes are joined you can query Etcd to see the auto-registration of hazelcast instances works, the service-id's generated etc
$ ./etcdctl ls hz-discovery-test-cluster

$ ./etcdctl get /hz-discovery-test-cluster/hz-discovery-test-cluster-
{"ip":"","port":5702,"hostname":"","registeredAt":"2015.11.25 14:25:59.026 +0000"}

Build from source

  • From the root of this project, build a Jar : ./gradlew assemble

  • Include the built jar artifact located at build/libs/hazelcast-etcd-discovery-spi-[VERSION].jar in your hazelcast project

  • If not already present in your hazelcast application's Maven (pom.xml) or Gradle (build.gradle) dependencies section; ensure that these dependencies are present (versions may vary as appropriate):

compile group: 'org.mousio', name: 'etcd4j', version:'2.9.0'
compile group: '', name: 'gson', version:'2.4'


It may also help you to understand the functionality by checking out and running the unit-tests located at src/test/java. BE SURE TO READ the comments as some of the tests require you to setup your local Etcd and edit certain files.

From the command line you can run TestExplicitIpPortRegistrator and TestLocalDiscoveryNodeRegistrator unit-tests by invoking the runTests task using gradlew that runs both tests and displays the result on the console.

$ ./gradlew runTests

The task above will display output indicating the test has started and whether the test has passed or failed.

Sample output for passing test:
org.bitsofinfo.hazelcast.discovery.etcd.TestExplicitIpPortRegistrator > testExplicitIpPortRegistrator STARTED

org.bitsofinfo.hazelcast.discovery.etcd.TestExplicitIpPortRegistrator > testExplicitIpPortRegistrator PASSED
Sample output for failing test:
org.bitsofinfo.hazelcast.discovery.etcd.TestDoNothingRegistrator > testDoNothingRegistrator STARTED

org.bitsofinfo.hazelcast.discovery.etcd.TestDoNothingRegistrator > testDoNothingRegistrator FAILED
    java.lang.AssertionError at

To run individual unit-test, use the test.single argument to provide the unit-test you would like to run. The command below runs the unit test for TestDoNothingRegistrator

$ ./gradlew test -Dtest.single=TestDoNothingRegistrator
Note on running TestDoNothingRegistrator unit-test

The TestDoNothingRegistrator unit-test should be run separately using the test.single argument as demonstrated above as it requires you to register a service with your local etcd with 5 nodes/instances. Please CAREFULLY READ the comments in to see how this test should be run.

Related info


Containerization (Docker) notes

This library may also be helpful to you: docker-discovery-registrator-consul

One of the main drivers for coding this module was for Hazelcast applications that were deployed as Docker containers that would need to automatically register themselves with Etcd for higher level cluster orchestration of the cluster.

If you are deploying your Hazelcast application as a Docker container, one helpful tip is that you will want to avoid hardwired configuration in the hazelcast XML config, but rather have your Docker container take startup arguments that would be translated to -D system properties on startup. Convienently Hazelcast can consume these JVM system properties and replace variable placeholders in the XML config. See this documentation for examples:

Specifically when using this discovery strategy and Docker, it may be useful for you to use the ExplicitIpPortRegistrator EtcdRegistrator instead of the LocalDiscoveryNodeRegistrator as the latter relies on hazelcast to determine its IP/PORT and this may end up being the local container IP, and not the Docker host IP, leading to a situation where a unreachable IP/PORT combination is published to Etcd.

Example: excerpt from explicitIpPortRegistrator-example.xml

Start your hazelcast app such as with the below, this would assume that hazelcast is actually reachable via this configuration via your Docker host and the port mappings that were specified on docker run. (i.e. the IP below would be your docker host/port that is mapped to the actual hazelcast app container and port it exposes for hazelcast).

This library may also be helpful to you: docker-discovery-registrator-consul

See this Docker issue for related info on detecting mapped ports/ip from within a container

java -jar myHzApp.jar -DregisterWithIpAddress=<dockerHostIp> -DregisterWithPort=<mappedContainerPortOnDockerHost> ....

<property name="etcd-registrator-config"><![CDATA[


Etcd based discovery strategy SPI for Hazelcast enabled applications




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