Trying something

cylc/flow/hostuserutil.py

@@ -113,24 +113,28 @@ def get_host_ip_by_name(target):
         """Return internal IP address of target."""
         return socket.gethostbyname(target)
 
+    @staticmethod
+    def resolve_macos_ip6_fqdn(target: str) -> str:
+        """Python's socket bindings don't play nicely with MacOS
+        so we sometimes get an ip6.arpa address from
+        socket.getfqdn.
+
+        Note that this does *not* match `hostname -f`.
+        https://github.com/cylc/cylc-flow/issues/2689
+        https://github.com/cylc/cylc-flow/issues/3768
+        """
+        if IS_MAC_OS and target == (
+            '1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.'
+            '0.0.0.0.0.0.ip6.arpa'
+        ):
+            return socket.gethostname()
+        return target
+
     def _get_host_info(self, target=None):
         """Return the extended info of the current host."""
         if target not in self._host_exs:
             if target is None:
-                target = socket.getfqdn()
-            if (
-                IS_MAC_OS
-                and target == (
-                    '1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.'
-                    '0.0.0.0.0.0.ip6.arpa'
-                )
-            ):
-                # Python's socket bindings don't play nicely with mac os
-                # so by default we get the above ip6.arpa address from
-                # socket.getfqdn, note this does *not* match `hostname -f`.
-                # https://github.com/cylc/cylc-flow/issues/2689
-                # https://github.com/cylc/cylc-flow/issues/3595
-                target = socket.gethostname()
+                target = self.resolve_macos_ip6_fqdn(socket.getfqdn())
             try:
                 self._host_exs[target] = socket.gethostbyname_ex(target)
             except IOError as exc:
@@ -202,12 +206,15 @@ def is_remote_host(self, name):
                 self._remote_hosts[name] = False
             else:
                 try:
-                    host_info = self._get_host_info(name)
+                    ip_addr = socket.gethostbyname(name)
                 except IOError:
                     self._remote_hosts[name] = True
                 else:
                     self._remote_hosts[name] = (
-                        host_info != self._get_host_info())
+                        ip_addr != socket.gethostbyname(
+                            self.resolve_macos_ip6_fqdn(socket.getfqdn())
+                        )
+                    )
         return self._remote_hosts[name]
 
     def is_remote_user(self, name):