host-local: allow ip request via CNI_ARGS

A specific IP can now be requested via the environment variable CNI_ARGS, e.g.
`CNI_ARGS=ip=1.2.3.4`.
The plugin will try to reserve the specified IP.
If this is not successful the execution will fail.

plugins/ipam/host-local/allocator.go

@@ -78,6 +78,40 @@ func (a *IPAllocator) Get(id string) (*plugin.IPConfig, error) {
 		gw = ip.NextIP(a.conf.Subnet.IP)
 	}
 
+	var requestedIP net.IP
+	if a.conf.Args != nil {
+		requestedIP = a.conf.Args.IP
+	}
+
+	if requestedIP != nil {
+		if gw != nil && gw.Equal(a.conf.Args.IP) {
+			return nil, fmt.Errorf("requested IP must differ gateway IP")
+		}
+
+		subnet := net.IPNet{
+			IP:   a.conf.Subnet.IP,
+			Mask: a.conf.Subnet.Mask,
+		}
+		err := validateRangeIP(requestedIP, &subnet)
+		if err != nil {
+			return nil, err
+		}
+
+		reserved, err := a.store.Reserve(id, requestedIP)
+		if err != nil {
+			return nil, err
+		}
+
+		if reserved {
+			return &plugin.IPConfig{
+				IP:      net.IPNet{requestedIP, a.conf.Subnet.Mask},
+				Gateway: gw,
+				Routes:  a.conf.Routes,
+			}, nil
+		}
+		return nil, fmt.Errorf("requested IP address %q is not available in network: %s", requestedIP, a.conf.Name)
+	}
+
 	for cur := a.start; !cur.Equal(a.end); cur = ip.NextIP(cur) {
 		// don't allocate gateway IP
 		if gw != nil && cur.Equal(gw) {
@@ -96,7 +130,6 @@ func (a *IPAllocator) Get(id string) (*plugin.IPConfig, error) {
 			}, nil
 		}
 	}
-
 	return nil, fmt.Errorf("no IP addresses available in network: %s", a.conf.Name)
 }
 

plugins/ipam/host-local/config.go

@@ -32,6 +32,11 @@ type IPAMConfig struct {
 	Subnet     ip.IPNet       `json:"subnet"`
 	Gateway    net.IP         `json:"gateway"`
 	Routes     []plugin.Route `json:"routes"`
+	Args       *IPAMArgs      `json:"-"`
+}
+
+type IPAMArgs struct {
+	IP net.IP `json:"ip",omitempty`
 }
 
 type Net struct {
@@ -40,12 +45,20 @@ type Net struct {
 }
 
 // NewIPAMConfig creates a NetworkConfig from the given network name.
-func LoadIPAMConfig(bytes []byte) (*IPAMConfig, error) {
+func LoadIPAMConfig(bytes []byte, args string) (*IPAMConfig, error) {
 	n := Net{}
 	if err := json.Unmarshal(bytes, &n); err != nil {
 		return nil, err
 	}
 
+	if args != "" {
+		ipamArgs := IPAMArgs{}
+		err := plugin.LoadArgs(args, &ipamArgs)
+		if err != nil {
+			return nil, err
+		}
+	}
+
 	if n.IPAM == nil {
 		return nil, fmt.Errorf("%q missing 'ipam' key")
 	}

plugins/ipam/host-local/main.go

@@ -28,7 +28,7 @@ func main() {
 }
 
 func cmdAdd(args *skel.CmdArgs) error {
-	ipamConf, err := LoadIPAMConfig(args.StdinData)
+	ipamConf, err := LoadIPAMConfig(args.StdinData, args.Args)
 	if err != nil {
 		return err
 	}
@@ -39,6 +39,13 @@ func cmdAdd(args *skel.CmdArgs) error {
 	}
 	defer store.Close()
 
+	ipamArgs := IPAMArgs{}
+	err = plugin.LoadArgs(args.Args, &ipamArgs)
+	if err != nil {
+		return err
+	}
+	ipamConf.Args = &ipamArgs
+
 	allocator, err := NewIPAllocator(ipamConf, store)
 	if err != nil {
 		return err
@@ -66,7 +73,7 @@ func cmdAdd(args *skel.CmdArgs) error {
 }
 
 func cmdDel(args *skel.CmdArgs) error {
-	ipamConf, err := LoadIPAMConfig(args.StdinData)
+	ipamConf, err := LoadIPAMConfig(args.StdinData, args.Args)
 	if err != nil {
 		return err
 	}