Automatically detects the Route Table ID

Route table ID is not required to be specified in the config. We
determine the subnetID the instance belongs to by using
describeInstances. We filter the DescribeRouteTables
request using the subnetID to find the RouteTableID. Autodetect functionality can be
overridden by manually passing routeTableID in as a configuration parameter.

Fixes #194

Godeps/_workspace/src/github.com/mitchellh/goamz/ec2/ec2.go

@@ -3101,7 +3101,9 @@ func (ec2 *EC2) DeleteRouteTable(id string) (resp *SimpleResp, err error) {
 // http://docs.aws.amazon.com/AWSEC2/latest/APIReference/ApiReference-query-DescribeRouteTables.html
 func (ec2 *EC2) DescribeRouteTables(ids []string, filter *Filter) (resp *RouteTablesResp, err error) {
 	params := makeParams("DescribeRouteTables")
-	addParamsList(params, "RouteTableId", ids)
+	if ids != nil {
+		addParamsList(params, "RouteTableId", ids)
+	}
 	filter.addParams(params)
 
 	resp = &RouteTablesResp{}

backend/awsvpc/awsvpc.go

@@ -84,7 +84,6 @@ func (m *AwsVpcBackend) Init(extIface *net.Interface, extIP net.IP) (*backend.Su
 	if err != nil {
 		return nil, fmt.Errorf("error getting EC2 instance identity: %v", err)
 	}
-
 	instanceID, ok := identity["instanceId"].(string)
 	if !ok {
 		return nil, fmt.Errorf("invalid EC2 instance ID: %v", identity["instanceId"])
@@ -103,19 +102,37 @@ func (m *AwsVpcBackend) Init(extIface *net.Interface, extIP net.IP) (*backend.Su
 	}
 	ec2c := ec2.New(auth, region)
 
+	if m.cfg.RouteTableID == "" {
+		log.Infof("RouteTableID not passed as config parameter, attempting to detect")
+		routeTableID, err := m.DetectRouteTableID(instanceID, ec2c)
+		if err != nil {
+			return nil, err
+		}
+		log.Info("Detected routeRouteTableID: ", routeTableID)
+
+		m.cfg.RouteTableID = routeTableID
+	}
+
 	filter := ec2.NewFilter()
 	filter.Add("route.destination-cidr-block", l.Subnet.String())
 	filter.Add("route.state", "active")
 
 	resp, err := ec2c.DescribeRouteTables([]string{m.cfg.RouteTableID}, filter)
 	if err != nil {
-		return nil, fmt.Errorf("error describing routeTables for %s: %v", l.Subnet.String(), err)
-	}
+		log.Errorf("Error describing route tables: %v", err)
 
-	for _, routeTable := range resp.RouteTables {
-		for _, route := range routeTable.Routes {
-			if l.Subnet.String() == route.DestinationCidrBlock && route.State == "active" {
-				log.Errorf("Matching *active* entry to: %s that will be deleted: %s, %s \n", l.Subnet.String(), route.DestinationCidrBlock, route.GatewayId)
+		if ec2Err, ok := err.(*ec2.Error); ok {
+			if ec2Err.Code == "UnauthorizedOperation" {
+				log.Errorf("Note: describeRouteTables permission cannot be bound to any resource")
+			}
+		}
+
+	} else {
+		for _, routeTable := range resp.RouteTables {
+			for _, route := range routeTable.Routes {
+				if l.Subnet.String() == route.DestinationCidrBlock && route.State == "active" {
+					log.Errorf("Matching *active* entry to: %s that will be deleted: %s, %s \n", l.Subnet.String(), route.DestinationCidrBlock, route.GatewayId)
+				}
 			}
 		}
 	}
@@ -145,6 +162,26 @@ func (m *AwsVpcBackend) Init(extIface *net.Interface, extIP net.IP) (*backend.Su
 	}, nil
 }
 
+func (m *AwsVpcBackend) DetectRouteTableID(instanceID string, ec2c *ec2.EC2) (string, error) {
+	resp, err := ec2c.Instances([]string{instanceID}, nil)
+	if err != nil {
+		return "", fmt.Errorf("error getting instance info: %v", err)
+	}
+
+	subnetID := resp.Reservations[0].Instances[0].SubnetId
+	log.Info("SubnetId: ", subnetID)
+
+	filter := ec2.NewFilter()
+	filter.Add("association.subnet-id", subnetID)
+
+	res, err := ec2c.DescribeRouteTables(nil, filter)
+	if err != nil {
+		return "", fmt.Errorf("error describing routeTables for subnetID %s: %v", subnetID, err)
+	}
+
+	return res.RouteTables[0].RouteTableId, nil
+}
+
 func (m *AwsVpcBackend) Run() {
 	subnet.LeaseRenewer(m.ctx, m.sm, m.network, m.lease)
 }