Ignore restapi.allowlist_include_members for POST /failsafe (#3113)

If only the leader can't access DCS its member key will expire and `POST /failsafe` requests might be rejected because of that.

Close #3096

patroni/api.py

@@ -37,13 +37,13 @@ from .utils import deep_compare, enable_keepalive, parse_bool, patch_config, Ret
 logger = logging.getLogger(__name__)
 
 
-def check_access(func: Callable[..., None]) -> Callable[..., None]:
+def check_access(*args: Any, **kwargs: Any) -> Callable[..., Any]:
     """Check the source ip, authorization header, or client certificates.
 
     .. note::
         The actual logic to check access is implemented through :func:`RestApiServer.check_access`.
 
-    :param func: function to be decorated.
+        Optionally it is possible to skip source ip check by specifying ``allowlist_check_members=False``.
 
     :returns: a decorator that executes *func* only if :func:`RestApiServer.check_access` returns ``True``.
 
@@ -60,19 +60,31 @@ def check_access(func: Callable[..., None]) -> Callable[..., None]:
         ...   @check_access
         ...   def do_PUT_foo(self):
         ...      print('In do_PUT_foo')
+        ...   @check_access(allowlist_check_members=False)
+        ...   def do_POST_bar(self):
+        ...      print('In do_POST_bar')
 
         >>> f = Foo()
         >>> f.do_PUT_foo()
         In FooServer: Foo
         In do_PUT_foo
-
     """
+    allowlist_check_members = kwargs.get('allowlist_check_members', True)
 
-    def wrapper(self: 'RestApiHandler', *args: Any, **kwargs: Any) -> None:
-        if self.server.check_access(self):
-            return func(self, *args, **kwargs)
+    def inner_decorator(func: Callable[..., None]) -> Callable[..., None]:
+        def wrapper(self: 'RestApiHandler', *args: Any, **kwargs: Any) -> None:
+            if self.server.check_access(self, allowlist_check_members=allowlist_check_members):
+                return func(self, *args, **kwargs)
 
-    return wrapper
+        return wrapper
+
+    # A hacky way to have decorators that work with and without parameters.
+    if len(args) == 1 and callable(args[0]):
+        # The first parameter is a function, it means decorator is used as "@check_access"
+        return inner_decorator(args[0])
+    else:
+        # @check_access(allowlist_check_members=False) case
+        return inner_decorator
 
 
 class RestApiHandler(BaseHTTPRequestHandler):
@@ -747,7 +759,7 @@ class RestApiHandler(BaseHTTPRequestHandler):
         else:
             self.send_error(502)
 
-    @check_access
+    @check_access(allowlist_check_members=False)
     def do_POST_failsafe(self) -> None:
         """Handle a ``POST`` request to ``/failsafe`` path.
 
@@ -1501,7 +1513,7 @@ class RestApiServer(ThreadingMixIn, HTTPServer, Thread):
                         except Exception as e:
                             logger.debug('Failed to parse url %s: %r', member.api_url, e)
 
-    def check_access(self, rh: RestApiHandler) -> Optional[bool]:
+    def check_access(self, rh: RestApiHandler, allowlist_check_members: bool = True) -> Optional[bool]:
         """Ensure client has enough privileges to perform a given request.
 
         Write a response back to the client if any issue is observed, and the HTTP status may be:
@@ -1514,12 +1526,17 @@ class RestApiServer(ThreadingMixIn, HTTPServer, Thread):
                 * a client certificate is expected by the server, but is missing in the request.
 
         :param rh: the request which access should be checked.
+        :param allowlist_check_members: whether we should check the source ip against existing cluster members.
 
         :returns: ``True`` if client access verification succeeded, otherwise ``None``.
         """
-        if self.__allowlist or self.__allowlist_include_members:
+        allowlist_check_members = allowlist_check_members and bool(self.__allowlist_include_members)
+        if self.__allowlist or allowlist_check_members:
             incoming_ip = ip_address(rh.client_address[0])
-            if not any(incoming_ip in net for net in self.__allowlist + tuple(self.__members_ips())):
+
+            members_ips = tuple(self.__members_ips()) if allowlist_check_members else ()
+
+            if not any(incoming_ip in net for net in self.__allowlist + members_ips):
                 return rh.write_response(403, 'Access is denied')
 
         if not hasattr(rh.request, 'getpeercert') or not rh.request.getpeercert():  # valid client cert isn't present