Macula UDP Multicast Gossip Cluster Strategy.

Zero-config cluster formation using UDP multicast for LAN discovery. Equivalent to libcluster's Cluster.Strategy.Gossip.

How It Works

Each node: 1. Joins a multicast group (default 230.1.1.251) 2. Periodically broadcasts its node name 3. Listens for broadcasts from other nodes 4. Connects to discovered nodes via Erlang distribution

Configuration

Start with options:

   {ok, _Pid} = macula_cluster_gossip:start_link(#{
       multicast_addr => {230, 1, 1, 251},  %% Multicast group
       port => 45892,                        %% UDP port
       broadcast_interval => 1500,           %% ms between broadcasts
       multicast_ttl => 1,                   %% TTL (1 = same subnet)
       secret => <<"my-cluster-secret">>     %% Optional: filter by secret
   }).

Or from environment variables:

   %% MACULA_GOSSIP_ADDR=230.1.1.251
   %% MACULA_GOSSIP_PORT=45892
   %% MACULA_GOSSIP_SECRET=my-cluster-secret
   {ok, _Pid} = macula_cluster_gossip:start_link(#{}).

Network Requirements

- Nodes must be on the same multicast-enabled network - UDP port must be open in firewalls - Multicast must be enabled on network interfaces - For Docker, use network_mode: host` or macvlan == Callbacks == Register a callback to receive cluster events: ``` {ok, _Pid} = macula_cluster_gossip:start_link(#{ callback => self() %% PID or {Module, Function} }). %% Receives: {macula_cluster, nodeup, Node} %% Receives: {macula_cluster, nodedown, Node}''