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/allocator_test.go

@@ -0,0 +1,136 @@
+// Copyright 2016 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 main
+
+import (
+	"github.com/containernetworking/cni/pkg/types"
+	fakestore "github.com/containernetworking/cni/plugins/ipam/host-local/backend/testing"
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+	"net"
+)
+
+type AllocatorTestCase struct {
+	subnet       string
+	ipmap        map[string]string
+	expectResult string
+	lastIP       string
+}
+
+func (t AllocatorTestCase) run() (*types.IPConfig, error) {
+	subnet, err := types.ParseCIDR(t.subnet)
+	conf := IPAMConfig{
+		Name:   "test",
+		Type:   "host-local",
+		Subnet: types.IPNet{IP: subnet.IP, Mask: subnet.Mask},
+	}
+	store := fakestore.NewFakeStore(t.ipmap, net.ParseIP(t.lastIP))
+	alloc, _ := NewIPAllocator(&conf, store)
+	res, err := alloc.Get("ID")
+	return res, err
+}
+
+var _ = Describe("host-local ip allocator", func() {
+	Context("when has free ip", func() {
+		It("should allocate ips in round robin", func() {
+			testCases := []AllocatorTestCase{
+				// fresh start
+				{
+					subnet:       "10.0.0.0/29",
+					ipmap:        map[string]string{},
+					expectResult: "10.0.0.2",
+					lastIP:       "",
+				},
+				{
+					subnet: "10.0.0.0/29",
+					ipmap: map[string]string{
+						"10.0.0.2": "id",
+					},
+					expectResult: "10.0.0.3",
+					lastIP:       "",
+				},
+				// next ip of last reserved ip
+				{
+					subnet:       "10.0.0.0/29",
+					ipmap:        map[string]string{},
+					expectResult: "10.0.0.7",
+					lastIP:       "10.0.0.6",
+				},
+				{
+					subnet: "10.0.0.0/29",
+					ipmap: map[string]string{
+						"10.0.0.5": "id",
+						"10.0.0.6": "id",
+					},
+					expectResult: "10.0.0.7",
+					lastIP:       "10.0.0.4",
+				},
+				// round robin to the beginning
+				{
+					subnet: "10.0.0.0/29",
+					ipmap: map[string]string{
+						"10.0.0.7": "id",
+					},
+					expectResult: "10.0.0.2",
+					lastIP:       "10.0.0.6",
+				},
+				// lastIP is out of range
+				{
+					subnet: "10.0.0.0/29",
+					ipmap: map[string]string{
+						"10.0.0.2": "id",
+					},
+					expectResult: "10.0.0.3",
+					lastIP:       "10.0.0.128",
+				},
+			}
+
+			for _, tc := range testCases {
+				res, err := tc.run()
+				Expect(err).ToNot(HaveOccurred())
+				Expect(res.IP.IP.String()).To(Equal(tc.expectResult))
+			}
+		})
+	})
+
+	Context("when out of ips", func() {
+		It("returns a meaningful error", func() {
+			testCases := []AllocatorTestCase{
+				{
+					subnet: "10.0.0.0/30",
+					ipmap: map[string]string{
+						"10.0.0.2": "id",
+						"10.0.0.3": "id",
+					},
+				},
+				{
+					subnet: "10.0.0.0/29",
+					ipmap: map[string]string{
+						"10.0.0.2": "id",
+						"10.0.0.3": "id",
+						"10.0.0.4": "id",
+						"10.0.0.5": "id",
+						"10.0.0.6": "id",
+						"10.0.0.7": "id",
+					},
+				},
+			}
+			for _, tc := range testCases {
+				_, err := tc.run()
+				Expect(err).To(MatchError("no IP addresses available in network: test"))
+			}
+		})
+	})
+})