Multicast

The Multicast registry center does not require starting any central node; as long as the broadcast addresses are the same, they can discover each other.

1 Usage Instructions

<dubbo:registry address="multicast://224.5.6.7:1234" />

or

<dubbo:registry protocol="multicast" address="224.5.6.7:1234" />

Note:

To reduce broadcast volume, Dubbo defaults to sending provider address information to consumers via unicast. If multiple consumer processes are started on one machine, the consumer must declare unicast=false, otherwise only one consumer will receive the message; when the provider and consumer run on the same machine, the consumer also needs to declare unicast=false, otherwise the consumer cannot receive messages, leading to the No provider available for the service exception:

<dubbo:application name="demo-consumer">
    <dubbo:parameter key="unicast" value="false" />
</dubbo:application>

or

<dubbo:consumer>
    <dubbo:parameter key="unicast" value="false" />
</dubbo:consumer>

2 Working Principle

2.1 Basic Process

0. The provider broadcasts its address when starting
1. The consumer broadcasts subscription requests when starting
2. When the provider receives a subscription request, it unicasts its address to the subscriber; if unicast=false is set, it broadcasts to the subscriber
3. The consumer connects to the address of the provider for RPC calls when it receives the provider address.

2.2 Usage Limitations

Multicast is limited by network structure and is only suitable for small-scale applications or use during the development phase. Multicast address range: 224.0.0.0 - 239.255.255.255