[WORKER] Support cleaner HAProxy config reloading

Stopping and restarting the HAProxy service will rudely terminate
any active sessions in HAProxy. This new method allows existing
connections to finish whatever they are doing while the configuration
file is reloaded.

Change-Id: Ife5d3ccc66349ea3393541768f12aedddb5ac5c8

libra/tests/mock_objects.py

@@ -19,6 +19,9 @@ class FakeOSServices(ServicesBase):
     def service_start(self):
         pass
 
+    def service_reload(self):
+        pass
+
     def write_config(self, config_str):
         pass
 
@@ -39,6 +42,9 @@ class FakeFaultingOSServices(ServicesBase):
     def service_start(self):
         raise Exception("fault")
 
+    def service_reload(self):
+        raise Exception("fault")
+
     def service_restart(self):
         raise Exception("fault")
 

libra/worker/drivers/haproxy/driver.py

@@ -336,8 +336,7 @@ class HAProxyDriver(LoadBalancerDriver):
 
     def create(self):
         self.ossvc.write_config(self._config_to_string())
-        self.ossvc.service_stop()
+        self.ossvc.service_reload()
-        self.ossvc.service_start()
 
     def suspend(self):
         self.ossvc.service_stop()

libra/worker/drivers/haproxy/services_base.py

@@ -38,6 +38,10 @@ class ServicesBase:
         """ Start the HAProxy service. """
         raise NotImplementedError()
 
+    def service_reload(self):
+        """ Reload the HAProxy config file. """
+        raise NotImplementedError()
+
     def write_config(self, config_str):
         """ Write the HAProxy configuration file. """
         raise NotImplementedError()

libra/worker/drivers/haproxy/ubuntu_services.py

@@ -58,6 +58,22 @@ class UbuntuServices(ServicesBase):
             raise Exception("%s does not exist. Start failed." %
                             self._haproxy_pid)
 
+    def service_reload(self):
+        """
+        Reload the HAProxy config file in a non-intrusive manner.
+
+        This assumes that /etc/init.d/haproxy is using the -sf option
+        to the haproxy process.
+        """
+        cmd = '/usr/bin/sudo -n /usr/sbin/service haproxy reload'
+        try:
+            subprocess.check_output(cmd.split())
+        except subprocess.CalledProcessError as e:
+            raise Exception("Failed to reload HAProxy config: %s" % e)
+        if not os.path.exists(self._haproxy_pid):
+            raise Exception("%s does not exist. Reload failed." %
+                            self._haproxy_pid)
+
     def sudo_copy(self, from_file, to_file):
         cmd = "/usr/bin/sudo -n /bin/cp %s %s" % (from_file, to_file)
         try: