plugins/ipam: round robin ip allocation for host-local ipam

This changes the ip allocation logic to round robin. Before this, host-local IPAM searched for available IPs from start of subnet. Hence it tends to allocate IPs that had been used recently. This is not ideal since it may cause collisions.

plugins/ipam/host-local/backend/disk/backend.go

@@ -15,12 +15,15 @@
 package disk
 
 import (
+	"fmt"
 	"io/ioutil"
 	"net"
 	"os"
 	"path/filepath"
 )
 
+const lastIPFile = "last_reserved_ip"
+
 var defaultDataDir = "/var/lib/cni/networks"
 
 type Store struct {
@@ -59,9 +62,25 @@ func (s *Store) Reserve(id string, ip net.IP) (bool, error) {
 		os.Remove(f.Name())
 		return false, err
 	}
+	// store the reserved ip in lastIPFile
+	ipfile := filepath.Join(s.dataDir, lastIPFile)
+	err = ioutil.WriteFile(ipfile, []byte(ip.String()), 0644)
+	if err != nil {
+		return false, err
+	}
 	return true, nil
 }
 
+// LastReservedIP returns the last reserved IP if exists
+func (s *Store) LastReservedIP() (net.IP, error) {
+	ipfile := filepath.Join(s.dataDir, lastIPFile)
+	data, err := ioutil.ReadFile(ipfile)
+	if err != nil {
+		return nil, fmt.Errorf("Failed to retrieve last reserved ip: %v", err)
+	}
+	return net.ParseIP(string(data)), nil
+}
+
 func (s *Store) Release(ip net.IP) error {
 	return os.Remove(filepath.Join(s.dataDir, ip.String()))
 }

plugins/ipam/host-local/backend/store.go

@@ -21,6 +21,7 @@ type Store interface {
 	Unlock() error
 	Close() error
 	Reserve(id string, ip net.IP) (bool, error)
+	LastReservedIP() (net.IP, error)
 	Release(ip net.IP) error
 	ReleaseByID(id string) error
 }

plugins/ipam/host-local/backend/testing/fake_store.go

@@ -0,0 +1,72 @@
+// Copyright 2015 CNI authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package testing
+
+import (
+	"net"
+)
+
+type FakeStore struct {
+	ipMap          map[string]string
+	lastReservedIP net.IP
+}
+
+func NewFakeStore(ipmap map[string]string, lastIP net.IP) *FakeStore {
+	return &FakeStore{ipmap, lastIP}
+}
+
+func (s *FakeStore) Lock() error {
+	return nil
+}
+
+func (s *FakeStore) Unlock() error {
+	return nil
+}
+
+func (s *FakeStore) Close() error {
+	return nil
+}
+
+func (s *FakeStore) Reserve(id string, ip net.IP) (bool, error) {
+	key := ip.String()
+	if _, ok := s.ipMap[key]; !ok {
+		s.ipMap[key] = id
+		s.lastReservedIP = ip
+		return true, nil
+	}
+	return false, nil
+}
+
+func (s *FakeStore) LastReservedIP() (net.IP, error) {
+	return s.lastReservedIP, nil
+}
+
+func (s *FakeStore) Release(ip net.IP) error {
+	delete(s.ipMap, ip.String())
+	return nil
+}
+
+func (s *FakeStore) ReleaseByID(id string) error {
+	toDelete := []string{}
+	for k, v := range s.ipMap {
+		if v == id {
+			toDelete = append(toDelete, k)
+		}
+	}
+	for _, ip := range toDelete {
+		delete(s.ipMap, ip)
+	}
+	return nil
+}