make subnet picking more robust

rezamt · Apr 30, 2020 · 407d42e · 407d42e
1 parent 7be97c1
commit 407d42e
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Showing 2 changed files with 56 additions and 19 deletions.
diff --git a/pkg/cluster/internal/providers/docker/network.go b/pkg/cluster/internal/providers/docker/network.go
@@ -18,8 +18,11 @@ package docker
 
 import (
 	"crypto/sha1"
+	"encoding/binary"
+	"errors"
 	"net"
 	"regexp"
+	"strings"
 
 	"sigs.k8s.io/kind/pkg/exec"
 )
@@ -38,33 +41,56 @@ const fixedNetworkName = "kind"
 func ensureNetwork(name string) error {
 	// TODO: the network might already exist and not have ipv6 ... :|
 	// discussion: https://github.com/kubernetes-sigs/kind/pull/1508#discussion_r414594198
-	out, err := exec.Output(exec.Command(
-		"docker", "network", "ls",
-		"--filter=name=^"+regexp.QuoteMeta(name)+"$",
-		"--format={{.Name}}",
-	))
+	exists, err := checkIfNetworkExists(name)
 	if err != nil {
 		return err
 	}
-	// network already exists
-	if string(out) == name+"\n" {
+	if exists {
 		return nil
 	}
 
 	// generate unique subnet per network based on the name
 	// obtained from the ULA fc00::/8 range
-	subnet := generateULASubnetFromName(name)
+	// make N attempts with "probing" in case we happen to collide
+	for i := int32(0); i < 3; i++ {
+		subnet := generateULASubnetFromName(name, i)
+		err = createNetwork(name, subnet)
+		if err == nil {
+			return nil
+		} else if !isPoolOverlapError(err) {
+			return err
+		}
+	}
+	return errors.New("exhausted attempts trying to find a non-overlapping subnet")
+}
 
+func createNetwork(name, subnet string) error {
 	return exec.Command("docker", "network", "create", "-d=bridge", "--ipv6", "--subnet", subnet, name).Run()
 }
 
-// generateULASubnetFromName generate an IPv6 subnet based on the name passed as parameter
-func generateULASubnetFromName(name string) string {
+func checkIfNetworkExists(name string) (bool, error) {
+	out, err := exec.Output(exec.Command(
+		"docker", "network", "ls",
+		"--filter=name=^"+regexp.QuoteMeta(name)+"$",
+		"--format={{.Name}}",
+	))
+	return strings.HasPrefix(string(out), name), err
+}
+
+func isPoolOverlapError(err error) bool {
+	rerr := exec.RunErrorForError(err)
+	return rerr != nil && strings.HasPrefix(string(rerr.Output), "Error response from daemon: Pool overlaps with other one on this address space")
+}
+
+// generateULASubnetFromName generate an IPv6 subnet based on the
+// name and Nth probing attempt
+func generateULASubnetFromName(name string, attempt int32) string {
 	ip := make([]byte, 16)
 	ip[0] = 0xfc
 	ip[1] = 0x00
 	h := sha1.New()
 	h.Write([]byte(name))
+	binary.Write(h, binary.LittleEndian, attempt)
 	bs := h.Sum(nil)
 	for i := 2; i < 8; i++ {
 		ip[i] = bs[i]

diff --git a/pkg/cluster/internal/providers/docker/network_test.go b/pkg/cluster/internal/providers/docker/network_test.go
@@ -17,41 +17,52 @@ limitations under the License.
 package docker
 
 import (
+	"fmt"
 	"testing"
 )
 
 func Test_generateULASubnetFromName(t *testing.T) {
 	t.Parallel()
 	cases := []struct {
-		name   string
-		subnet string
+		name    string
+		attempt int32
+		subnet  string
 	}{
 		{
 			name:   "kind",
-			subnet: "fc00:5ae0:f40:c847::/64",
+			subnet: "fc00:f853:ccd:e793::/64",
+		},
+		{
+			name:    "foo",
+			attempt: 1,
+			subnet:  "fc00:8edf:7f02:ec8f::/64",
+		},
+		{
+			name:    "foo",
+			attempt: 2,
+			subnet:  "fc00:9968:306b:2c65::/64",
 		},
 		{
 			name:   "kind2",
-			subnet: "fc00:cadf:7baf:98ea::/64",
+			subnet: "fc00:444c:147a:44ab::/64",
 		},
 		{
 			name:   "kin",
-			subnet: "fc00:f804:3187:7254::/64",
+			subnet: "fc00:fcd9:c2be:8e23::/64",
 		},
 		{
 			name:   "mysupernetwork",
-			subnet: "fc00:1dd9:697c:314e::/64",
+			subnet: "fc00:7ae1:1e0d:b4d4::/64",
 		},
 	}
 	for _, tc := range cases {
 		tc := tc // capture variable
-		t.Run(tc.name, func(t *testing.T) {
+		t.Run(fmt.Sprintf("%s,%d", tc.name, tc.attempt), func(t *testing.T) {
 			t.Parallel()
-			subnet := generateULASubnetFromName(tc.name)
+			subnet := generateULASubnetFromName(tc.name, tc.attempt)
 			if subnet != tc.subnet {
 				t.Errorf("Wrong subnet from %v: expected %v, received %v", tc.name, tc.subnet, subnet)
 			}
-
 		})
 	}
 }