Move create of ComputeAPI object in websocketproxy

Currently, we create a compute.rpcapi.ComputeAPI object during
NovaProxyRequestHandler.__init__ in order to make calls to nova-compute
for console token authorizations (port validation). This is problematic
in the event that we receive a TCP RST as it results in constructing a
ComputeAPI object only to throw it away and a large number of TCP RST
sent can cause excessive resource consumption.

This moves the creation of the ComputeAPI object from __init__ to being
lazily instantiated upon first use by access of a property, thus
avoiding creation of ComputeAPI objects when we receive TCP RST
messages.

Closes-Bug: #1816727

Change-Id: I3fe5540ea460fb32767b5e681295fdaf89ce17c5
(cherry picked from commit e4fa061f17353f49615d4850b562699d55a0641b)
(cherry picked from commit b1b28169af9f835f5b99a4d70d1c0eff2d9fc2f4)

nova/console/websocketproxy.py

@@ -304,12 +304,18 @@ class NovaProxyRequestHandlerBase(object):
 class NovaProxyRequestHandler(NovaProxyRequestHandlerBase,
                               websockify.ProxyRequestHandler):
     def __init__(self, *args, **kwargs):
-        # Order matters here. ProxyRequestHandler.__init__() will eventually
-        # call new_websocket_client() and we need self.compute_rpcapi set
-        # before then.
-        self.compute_rpcapi = compute_rpcapi.ComputeAPI()
+        self._compute_rpcapi = None
         websockify.ProxyRequestHandler.__init__(self, *args, **kwargs)
 
+    @property
+    def compute_rpcapi(self):
+        # Lazy load the rpcapi/ComputeAPI upon first use for this connection.
+        # This way, if we receive a TCP RST, we will not create a ComputeAPI
+        # object we won't use.
+        if not self._compute_rpcapi:
+            self._compute_rpcapi = compute_rpcapi.ComputeAPI()
+        return self._compute_rpcapi
+
     def socket(self, *args, **kwargs):
         return websockify.WebSocketServer.socket(*args, **kwargs)
 

nova/tests/unit/console/test_websocketproxy.py

@@ -706,6 +706,16 @@ class NovaProxyRequestHandlerBaseTestCase(test.NoDBTestCase):
         self.wh.socket.assert_called_with('node1', 10000, connect=True)
         self.wh.do_proxy.assert_called_with('<socket>')
 
+    def test_tcp_rst_no_compute_rpcapi(self):
+        # Tests that we don't create a ComputeAPI object if we receive a
+        # TCP RST message. Simulate by raising the socket.err upon recv.
+        err = socket.error('[Errno 104] Connection reset by peer')
+        self.wh.socket.recv.side_effect = err
+        conn = mock.MagicMock()
+        address = mock.MagicMock()
+        self.wh.server.top_new_client(conn, address)
+        self.assertIsNone(self.wh._compute_rpcapi)
+
 
 class NovaWebsocketSecurityProxyTestCase(test.NoDBTestCase):