[WORKER] Active monitoring support

Support active (HTTP) monitoring in addition to passive (CONNECT)
tcp monitoring. If no monitoring for a load balancer is defined,
we always use a simple tcp-only monitor.

Change-Id: Ib2d4e87097069a4fec5c307bf2718ec1954ebf10

libra/worker/controller.py

@@ -171,6 +171,36 @@ class LBaaSController(object):
                 self.msg[self.RESPONSE_FIELD] = self.RESPONSE_FAILURE
                 return self.msg
 
+            if 'monitor' in current_lb:
+                monitor = current_lb['monitor']
+                for opt in ['type', 'delay', 'timeout', 'attempts']:
+                    if opt not in monitor:
+                        return BadRequest("Missing monitor value '%s'" %
+                                          opt).to_json()
+                if 'path' not in monitor:
+                    monitor['path'] = '/'
+
+                try:
+                    self.driver.add_monitor(current_lb['protocol'],
+                                            monitor['type'],
+                                            monitor['delay'],
+                                            monitor['timeout'],
+                                            monitor['attempts'],
+                                            monitor['path'])
+                except NotImplementedError:
+                    self.logger.error(
+                        "Selected driver does not support adding healthchecks."
+                    )
+                    self.msg[self.RESPONSE_FIELD] = self.RESPONSE_FAILURE
+                    return self.msg
+                except Exception as e:
+                    self.logger.error(
+                        "Selected driver failed adding healthchecks: %s, %s" %
+                        (e.__class__, e)
+                    )
+                    self.msg[self.RESPONSE_FIELD] = self.RESPONSE_FAILURE
+                    return self.msg
+
             for lb_node in current_lb['nodes']:
                 port, address, node_id, weight = None, None, None, None