hazelcast-etcd-discovery-spi

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.

• Status
• Releases
• Requirements
• Maven/Gradle install
• Features
• Usage
• Build from source
• Unit tests
• Related Info
• Todo
• Notes
• Docker info

Status

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

Releases

• 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

Requirements

• Java 6+
• Hazelcast 3.6+
• Etcd

Maven/Gradle

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

Gradle:

repositories {
    jcenter() 
}

dependencies {
	compile 'org.bitsofinfo:hazelcast-etcd-discovery-spi:1.0-RC2'
}

Maven:

<dependencies>
    <dependency>
        <groupId>org.bitsofinfo</groupId>
        <artifactId>hazelcast-etcd-discovery-spi</artifactId>
        <version>1.0-RC2</version>
    </dependency>
</dependencies>

<repositories>
    <repository>
        <snapshots>
            <enabled>false</enabled>
        </snapshots>
        <id>central</id>
        <name>bintray</name>
        <url>http://jcenter.bintray.com</url>
    </repository>
</repositories>

Features

• 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":"my.host", "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

Usage

• 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:

./etcd

• 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 ManualRunner.java example.

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

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

     <discovery-strategies>
       <discovery-strategy enabled="true"
           class="org.bitsofinfo.hazelcast.discovery.etcd.EtcdDiscoveryStrategy">

         <properties>
              <property name="etcd-uris">http://localhost:4001</property>
		      <property name="etcd-service-name">hz-discovery-test-cluster</property>
              <property name="etcd-registrator">org.bitsofinfo.hazelcast.discovery.etcd.LocalDiscoveryNodeRegistrator</property>
		      <property name="etcd-registrator-config"><![CDATA[
					{
					  "preferPublicAddress":false
					}
              ]]></property>
        </properties>
      </discovery-strategy>
    </discovery-strategies>

  </join>
</network>

• 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
/hz-discovery-test-cluster/hz-discovery-test-cluster-192.168.0.208-192.168.0.208-5701

$ ./etcdctl get /hz-discovery-test-cluster/hz-discovery-test-cluster-192.168.0.208-192.168.0.208-5701
{"ip":"192.168.0.208","port":5702,"hostname":"192.168.0.208","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: 'com.google.code.gson', name: 'gson', version:'2.4'

Unit-tests

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 TestDoNothingRegistrator.java:85

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 TestDoNothingRegistrator.java to see how this test should be run.

Related info

• https://github.com/coreos/etcd
• https://github.com/jurmous/etcd4j
• http://docs.hazelcast.org/docs/3.6/manual/html-single/index.html#discovery-spi
• Consul version of this: https://github.com/bitsofinfo/hazelcast-consul-discovery-spi

Notes

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: http://docs.hazelcast.org/docs/3.6/manual/html-single/index.html#using-variables

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[
      {
        "registerWithIpAddress":"${registerWithIpAddress}",
        "registerWithPort":${registerWithPort}
      }
  ]]></property>