Filtering Members with Attributes

You can define various member attributes on your Hazelcast members. You can use these member attributes to tag your members as may be required by your business logic.

To define a member attribute on a member, you can:

  • provide MemberAttributeConfig to your Config object

  • or provide the member attributes at runtime via attribute setter methods on the Member interface. For example, you can tag your members with their CPU characteristics and you can route CPU intensive tasks to those CPU-rich members. Here is how you can do it:

public class ExampleMemberAttributes {
    public static void main(String[] args) {
        MemberAttributeConfig fourCore = new MemberAttributeConfig();
        memberAttributeConfig.setAttribute( "CPU_CORE_COUNT", "4" );
        MemberAttributeConfig twelveCore = new MemberAttributeConfig();
        memberAttributeConfig.setAttribute( "CPU_CORE_COUNT", "12" );
        MemberAttributeConfig twentyFourCore = new MemberAttributeConfig();
        memberAttributeConfig.setAttribute( "CPU_CORE_COUNT", "24" );
        Config member1Config = new Config();
        config.setMemberAttributeConfig( fourCore );
        Config member2Config = new Config();
        config.setMemberAttributeConfig( twelveCore );
        Config member3Config = new Config();
        config.setMemberAttributeConfig( twentyFourCore );
        HazelcastInstance member1 = Hazelcast.newHazelcastInstance( member1Config );
        HazelcastInstance member2 = Hazelcast.newHazelcastInstance( member2Config );
        HazelcastInstance member3 = Hazelcast.newHazelcastInstance( member3Config );
        IExecutorService executorService = member1.getExecutorService( "processor" );
        executorService.execute( new CPUIntensiveTask(), new MemberSelector() {
            @Override
            public boolean select(Member member) {
                int coreCount = Integer.parseInt(member.getAttribute( "CPU_CORE_COUNT" ));
                // Task will be executed at either member2 or member3
                if ( coreCount > 8 ) {
                    return true;
                }
                return false;
            }
        } );
        HazelcastInstance member4 = Hazelcast.newHazelcastInstance();
        // We can also set member attributes at runtime.
        member4.setAttribute( "CPU_CORE_COUNT", "2" );
    }
}

For another example, you can tag some members with a filter so that a member in the cluster can load classes from those tagged members. See the User Code Deployment section for more information.

You can also define your member attributes through declarative configuration and start your member afterwards. Here is how you can use the declarative approach:

  • XML

  • YAML

<hazelcast>
    ...
    <member-attributes>
        <attribute name="CPU_CORE_COUNT">4</attribute-name>
    </member-attributes>
    ...
</hazelcast>
hazelcast:
  member-attributes:
    CPU_CORE_COUNT:
      type: int
      value: 4