query host to check if dhcp rehydration feature is enabled and skip sending workaround dhcp request if so

Author: QxBytes

dhcp/dhcp_linux.go

@@ -10,6 +10,8 @@ import (
 	"encoding/binary"
 	"io"
 	"net"
+	"net/http"
+	"strings"
 	"time"
 
 	"github.com/pkg/errors"
@@ -37,6 +39,9 @@ const (
 	hops          = 0
 	secs          = 0
 	flags         = 0x8000 // Broadcast flag
+
+	nmAgentSupportedApisURL = "http://168.63.129.16/machine/plugins/?comp=nmagent&type=GetSupportedApis"
+	dhcpRehydrationAPIStr   = "SwiftV2DhcpRehydrationFromGoalState" // Set value provided by host
 )
 
 // TransactionID represents a 4-byte DHCP transaction ID as defined in RFC 951,
@@ -49,6 +54,8 @@ var (
 	magicCookie        = []byte{0x63, 0x82, 0x53, 0x63} // DHCP magic cookie
 	DefaultReadTimeout = 3 * time.Second
 	DefaultTimeout     = 3 * time.Second
+
+	errResponseNotOK = errors.New("not ok http status")
 )
 
 type DHCP struct {
@@ -459,3 +466,37 @@ func (c *DHCP) DiscoverRequest(ctx context.Context, mac net.HardwareAddr, ifname
 	res := c.receiveDHCPResponse(ctx, reader, txid)
 	return res
 }
+
+// DHCPRehydrationFeatureOnHost queries the host to check if a particular API is supported,
+// and if so, returns true; if we are unable to determine if the feature is enabled, an error
+// is returned
+func (c *DHCP) DHCPRehydrationFeatureOnHost(ctx context.Context) (bool, error) {
+	var (
+		resp       *http.Response
+		httpClient = &http.Client{Timeout: DefaultTimeout}
+	)
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, nmAgentSupportedApisURL, nil)
+	if err != nil {
+		return false, errors.Wrap(err, "failed to create http request")
+	}
+	req.Header.Add("Metadata", "true")
+	req.Header.Add("x-ms-version", "2012-11-30")
+	resp, err = httpClient.Do(req)
+	if err != nil {
+		return false, errors.Wrap(err, "error issuing http request")
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		return false, errResponseNotOK
+	}
+	bytes, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return false, errors.Wrap(err, "failed to read response body")
+	}
+	str := string(bytes)
+	if !strings.Contains(str, dhcpRehydrationAPIStr) {
+		return false, nil
+	}
+
+	return true, nil
+}

dhcp/dhcp_windows.go

@@ -20,3 +20,7 @@ func New(logger *zap.Logger) *DHCP {
 func (c *DHCP) DiscoverRequest(_ context.Context, _ net.HardwareAddr, _ string) error {
 	return nil
 }
+
+func (c *DHCP) DHCPRehydrationFeatureOnHost(ctx context.Context) (bool, error) {
+	return false, nil
+}

network/dhcp.go

@@ -7,10 +7,15 @@ import (
 
 type dhcpClient interface {
 	DiscoverRequest(context.Context, net.HardwareAddr, string) error
+	DHCPRehydrationFeatureOnHost(context.Context) (bool, error)
 }
 
 type mockDHCP struct{}
 
-func (netns *mockDHCP) DiscoverRequest(context.Context, net.HardwareAddr, string) error {
+func (d *mockDHCP) DiscoverRequest(context.Context, net.HardwareAddr, string) error {
 	return nil
 }
+
+func (d *mockDHCP) DHCPRehydrationFeatureOnHost(context.Context) (bool, error) {
+	return false, nil
+}

network/secondary_endpoint_client_linux.go

@@ -138,12 +138,21 @@ func (client *SecondaryEndpointClient) ConfigureContainerInterfacesAndRoutes(epI
 	timeout := time.Duration(numSecs) * time.Second
 	ctx, cancel := context.WithDeadline(context.Background(), time.Now().Add(timeout))
 	defer cancel()
-	logger.Info("Sending DHCP packet", zap.Any("macAddress", epInfo.MacAddress), zap.String("ifName", epInfo.IfName))
-	err := client.dhcpClient.DiscoverRequest(ctx, epInfo.MacAddress, epInfo.IfName)
+
+	// check if the permanent fix on the host has already rolled out
+	dhcpRehydrationFeatureEnabled, err := client.dhcpClient.DHCPRehydrationFeatureOnHost(ctx)
 	if err != nil {
-		return errors.Wrapf(err, "failed to issue dhcp discover packet to create mapping in host")
+		return errors.Wrap(err, "could not determine if dhcp rehydration feature enabled on host")
+	}
+	// only send the dhcp packet if the host does not have the permanent fix
+	if !dhcpRehydrationFeatureEnabled {
+		logger.Info("Sending DHCP packet", zap.Any("macAddress", epInfo.MacAddress), zap.String("ifName", epInfo.IfName))
+		err := client.dhcpClient.DiscoverRequest(ctx, epInfo.MacAddress, epInfo.IfName)
+		if err != nil {
+			return errors.Wrap(err, "failed to issue dhcp discover packet to create mapping in host")
+		}
+		logger.Info("Finished configuring container interfaces and routes for secondary endpoint client")
 	}
-	logger.Info("Finished configuring container interfaces and routes for secondary endpoint client")
 
 	return nil
 }