Add "request_queue_size" option to REST API server (#2643)

Sets request queue size for TCP socket used by Patroni REST API. Once the queue is full, further requests get a "Connection denied" error. The default value is 5.

docs/ENVIRONMENT.rst

@@ -187,6 +187,8 @@ REST API
 -  **PATRONI\_RESTAPI\_ALLOWLIST\_INCLUDE\_MEMBERS**: (optional): If set to ``true`` it allows accessing unsafe REST API endpoints from other cluster members registered in DCS (IP address or hostname is taken from the members ``api_url``). Be careful, it might happen that OS will use a different IP for outgoing connections.
 -  **PATRONI\_RESTAPI\_HTTP\_EXTRA\_HEADERS**: (optional) HTTP headers let the REST API server pass additional information with an HTTP response.
 -  **PATRONI\_RESTAPI\_HTTPS\_EXTRA\_HEADERS**: (optional) HTTPS headers let the REST API server pass additional information with an HTTP response when TLS is enabled. This will also pass additional information set in ``http_extra_headers``.
+-  **PATRONI\_RESTAPI\_REQUEST\_QUEUE\_SIZE**: (optional): Sets request queue size for TCP socket used by Patroni REST API.  Once the queue is full, further requests get a "Connection denied" error. The default value is 5.
+- ```
 
 CTL
 ---

docs/SETTINGS.rst

@@ -352,6 +352,7 @@ REST API
         -  **allowlist\_include\_members**: (optional): If set to ``true`` it allows accessing unsafe REST API endpoints from other cluster members registered in DCS (IP address or hostname is taken from the members ``api_url``). Be careful, it might happen that OS will use a different IP for outgoing connections.
         -  **http\_extra\_headers**: (optional): HTTP headers let the REST API server pass additional information with an HTTP response.
         -  **https\_extra\_headers**: (optional): HTTPS headers let the REST API server pass additional information with an HTTP response when TLS is enabled. This will also pass additional information set in ``http_extra_headers``.
+        -  **request_queue_size**: (optional): Sets request queue size for TCP socket used by Patroni REST API.  Once the queue is full, further requests get a "Connection denied" error. The default value is 5.
 
 Here is an example of both **http_extra_headers** and **https_extra_headers**:
 

patroni/api.py

@@ -759,6 +759,7 @@ class RestApiServer(ThreadingMixIn, HTTPServer, Thread):
     def __init__(self, patroni, config):
         self.patroni = patroni
         self.__listen = None
+        self.request_queue_size = int(config.get('request_queue_size', 5))
         self.__ssl_options = None
         self.__ssl_serial_number = None
         self._received_new_cert = False

patroni/config.py

@@ -378,7 +378,8 @@ class Config(object):
 
         _set_section_values('restapi', ['listen', 'connect_address', 'certfile', 'keyfile', 'keyfile_password',
                                         'cafile', 'ciphers', 'verify_client', 'http_extra_headers',
-                                        'https_extra_headers', 'allowlist', 'allowlist_include_members'])
+                                        'https_extra_headers', 'allowlist', 'allowlist_include_members',
+                                        'request_queue_size'])
         _set_section_values('ctl', ['insecure', 'cacert', 'certfile', 'keyfile', 'keyfile_password'])
         _set_section_values('postgresql', ['listen', 'connect_address', 'proxy_address',
                                            'config_dir', 'data_dir', 'pgpass', 'bin_dir'])
@@ -393,12 +394,14 @@ class Config(object):
                 if value is not None:
                     ret[first][second] = value
 
-        for second in ('max_queue_size', 'file_size', 'file_num'):
-            value = ret.get('log', {}).pop(second, None)
-            if value:
-                value = parse_int(value)
-                if value is not None:
-                    ret['log'][second] = value
+        for first, params in (('restapi', ('request_queue_size',)),
+                              ('log', ('max_queue_size', 'file_size', 'file_num'))):
+            for second in params:
+                value = ret.get(first, {}).pop(second, None)
+                if value:
+                    value = parse_int(value)
+                    if value is not None:
+                        ret[first][second] = value
 
         def _parse_list(value):
             if not (value.strip().startswith('-') or '[' in value):

patroni/validator.py

@@ -703,7 +703,8 @@ schema = Schema({
     "scope": str,
     "restapi": {
         "listen": validate_host_port_listen,
-        "connect_address": validate_connect_address
+        "connect_address": validate_connect_address,
+        Optional("request_queue_size"): lambda i: assert_(0 <= int(i) <= 4096)
     },
     Optional("bootstrap"): {
         "dcs": {