Fix Erlang clustering: use IP-based node names with DNS strategy

DNSSRV strategy resolves to IP-based names but nodes were named by
pod name, causing connection failures. Switch to DNS strategy with
IP-based node naming so libcluster discovery matches actual node names.

config/runtime.exs

@@ -153,15 +153,14 @@ if config_env() == :prod do
 
   # Configure libcluster topology based on environment
   if cluster_enabled do
-    # Use DNSSRV strategy for StatefulSet clustering
+    # Use DNS strategy with headless service for node discovery
     config :libcluster,
       topologies: [
         k8s: [
-          strategy: Cluster.Strategy.Kubernetes.DNSSRV,
+          strategy: Cluster.Strategy.Kubernetes.DNS,
           config: [
-            service: "aprs-headless",
+            service: "aprs-headless.aprs.svc.cluster.local",
             application_name: "aprsme",
-            namespace: "aprs",
             polling_interval: 5_000
           ]
         ]

k8s/deployment.yaml

@@ -114,6 +114,10 @@ spec:
               valueFrom:
                 fieldRef:
                   fieldPath: metadata.name
+            - name: POD_IP
+              valueFrom:
+                fieldRef:
+                  fieldPath: status.podIP
             - name: PORT
               value: "4000"
             - name: PHX_HOST

rel/env.sh.eex

@@ -18,10 +18,10 @@
 # RELEASE_DISTRIBUTION must be "sname" (local), "name" (distributed) or "none".
 export RELEASE_DISTRIBUTION=name
 
-# Check if we're in Kubernetes (POD_NAME will be set)
-if [ -n "$POD_NAME" ]; then
-  # Use Kubernetes pod name and headless service for clustering
-  export RELEASE_NODE=${RELEASE_NODE:-<%= @release.name %>@${POD_NAME}.aprs-headless.aprs.svc.cluster.local}
+# Check if we're in Kubernetes (POD_IP will be set)
+if [ -n "$POD_IP" ]; then
+  # Use pod IP for Erlang distribution — matches libcluster DNS strategy
+  export RELEASE_NODE=${RELEASE_NODE:-<%= @release.name %>@${POD_IP}}
 else
   # Fallback to Dokku naming for non-Kubernetes deployments
   export RELEASE_NODE=<%= @release.name %>@${DOKKU_APP_NAME:-aprsme}.web.${DOKKU_APP_INSTANCE:-1}