chore: start deprecating mcast cluster discovery

apps/emqx_conf/src/emqx_conf_schema.erl

@@ -143,7 +143,7 @@ fields("cluster") ->
             )},
         {"discovery_strategy",
             sc(
-                hoconsc:enum([manual, static, mcast, dns, etcd, k8s]),
+                hoconsc:enum([manual, static, dns, etcd, k8s, mcast]),
                 #{
                     default => manual,
                     desc => ?DESC(cluster_discovery_strategy),
@@ -198,7 +198,7 @@ fields("cluster") ->
         {"mcast",
             sc(
                 ?R_REF(cluster_mcast),
-                #{}
+                #{importance => ?IMPORTANCE_HIDDEN}
             )},
         {"dns",
             sc(

rel/i18n/emqx_conf_schema.hocon

@@ -755,7 +755,9 @@ cluster_discovery_strategy.desc:
 - static: Configure static nodes list by setting <code>seeds</code> in config file.<br/>
 - dns: Use DNS A record to discover peer nodes.<br/>
 - etcd: Use etcd to discover peer nodes.<br/>
-- k8s: Use Kubernetes API to discover peer pods."""
+- k8s: Use Kubernetes API to discover peer pods.
+- mcast: Deprecated since 5.1, will be removed in 5.2.
+  This supports discovery via UDP multicast."""
 
 cluster_discovery_strategy.label:
 """Cluster Discovery Strategy"""