Validate demotion successor against peer map

plugins/postgresql/plugin.py

@@ -625,6 +625,36 @@ def demote_prepare(config, runtime_state, request_parameters):
             "node": node_name,
         }
 
+    try:
+        peers = parse_replication_peers(
+            config.get("PG_REPLICATION_PEERS", "")
+        )
+    except (TypeError, ValueError):
+        return {
+            "ocf_rc": 1,
+            "ready": False,
+            "reason": "peer_map_invalid",
+            "node": node_name,
+            "successor_node": successor_node,
+        }
+
+    successor_peer = next(
+        (
+            peer for peer in peers
+            if peer["name"].strip().lower() == successor_node
+        ),
+        None,
+    )
+
+    if successor_peer is None:
+        return {
+            "ocf_rc": 1,
+            "ready": False,
+            "reason": "successor_not_configured",
+            "node": node_name,
+            "successor_node": successor_node,
+        }
+
     return {
         "ocf_rc": 0,
         "ready": False,
@@ -634,8 +664,11 @@ def demote_prepare(config, runtime_state, request_parameters):
         "node": node_name,
         "target_node": target_node,
         "successor_node": successor_node,
+        "successor_host": successor_peer["host"],
+        "successor_port": successor_peer["port"],
         "age_seconds": age,
         "checks": {
+            "peer_map": True,
             "notification": True,
             "local_target": True,
             "successor_selected": True,