fix: prevent endless loop with DHCP requests in networkd

There were two problems:

* `configureInterfaces` was always failing if interface is already set
up, as the routes already exist

* `renew` was halving the renew interval each time `configureInterface`
fails, which starts at (LeaseTime/2) and goes effectively to zero

This was leading to high networkd CPU usage, storm of DHCP requests on
the network.

Signed-off-by: Andrey Smirnov <smirnov.andrey@gmail.com>

internal/app/networkd/pkg/address/dhcp.go

@@ -46,9 +46,11 @@ func (d *DHCP) Link() *net.Interface {
 // Discover handles the DHCP client exchange stores the DHCP Ack.
 func (d *DHCP) Discover(ctx context.Context, link *net.Interface) error {
 	d.NetIf = link
-	// TODO do something with context
+	ack, err := d.discover(ctx)
-	ack, err := d.discover()
+
-	d.Ack = ack
+	if ack != nil {
+		d.Ack = ack
+	}
 
 	return err
 }
@@ -191,7 +193,7 @@ func (d *DHCP) Hostname() (hostname string) {
 }
 
 // discover handles the actual DHCP conversation.
-func (d *DHCP) discover() (*dhcpv4.DHCPv4, error) {
+func (d *DHCP) discover(ctx context.Context) (*dhcpv4.DHCPv4, error) {
 	opts := []dhcpv4.OptionCode{
 		dhcpv4.OptionClasslessStaticRoute,
 		dhcpv4.OptionDomainNameServer,
@@ -223,7 +225,7 @@ func (d *DHCP) discover() (*dhcpv4.DHCPv4, error) {
 	// nolint: errcheck
 	defer cli.Close()
 
-	lease, err := cli.Request(context.Background(), mods...)
+	lease, err := cli.Request(ctx, mods...)
 	if err != nil {
 		// TODO: Make this a well defined error so we can make it not fatal
 		log.Printf("failed dhcp request for %q: %v", d.NetIf.Name, err)
@@ -231,5 +233,21 @@ func (d *DHCP) discover() (*dhcpv4.DHCPv4, error) {
 		return nil, err
 	}
 
+	log.Printf("DHCP ACK on %q: %s", d.NetIf.Name, collapseSummary(lease.ACK.Summary()))
+
 	return lease.ACK, err
 }
+
+func collapseSummary(summary string) string {
+	lines := strings.Split(summary, "\n")[1:]
+
+	for i := range lines {
+		lines[i] = strings.TrimSpace(lines[i])
+	}
+
+	if len(lines) > 0 && lines[len(lines)-1] == "" {
+		lines = lines[:len(lines)-1]
+	}
+
+	return strings.Join(lines, ", ")
+}

internal/app/networkd/pkg/nic/netlink.go

@@ -48,6 +48,10 @@ func (n *NetworkInterface) setMTU(idx int, mtu uint32) error {
 		return err
 	}
 
+	if msg.Attributes != nil && msg.Attributes.MTU == mtu {
+		return nil
+	}
+
 	err = n.rtConn.Link.Set(&rtnetlink.LinkMessage{
 		Family: msg.Family,
 		Type:   msg.Type,

internal/app/networkd/pkg/nic/nic.go

@@ -312,18 +312,26 @@ func (n *NetworkInterface) Renew() {
 // address TTL. If that fails, we'll continue to attempt to retry every
 // halflife.
 func (n *NetworkInterface) renew(method address.Addressing) {
+	const minRenewDuration = 5 * time.Second // protect from renewing too often
+
 	renewDuration := method.TTL() / 2
 
 	var err error
 
 	for {
-		<-time.After(renewDuration)
+		time.Sleep(renewDuration)
 
 		if err = n.configureInterface(method, n.Link); err != nil {
+			log.Printf("failure to renew address for %q: %s", n.Name, err)
+
 			renewDuration = (renewDuration / 2)
 		} else {
 			renewDuration = method.TTL() / 2
 		}
+
+		if renewDuration < minRenewDuration {
+			renewDuration = minRenewDuration
+		}
 	}
 }
 
@@ -337,7 +345,7 @@ func (n *NetworkInterface) configureInterface(method address.Addressing, link *n
 
 	// Set link MTU in any case
 	if err = n.setMTU(method.Link().Index, method.MTU()); err != nil {
-		return err
+		return fmt.Errorf("error setting MTU %d on %q: %w", method.MTU(), n.Name, err)
 	}
 
 	if discoverErr != nil {
@@ -368,7 +376,7 @@ func (n *NetworkInterface) configureInterface(method address.Addressing, link *n
 				switch err := err.(type) {
 				case *netlink.OpError:
 					if !os.IsExist(err.Err) && err.Err != syscall.ESRCH {
-						return err
+						return fmt.Errorf("error adding address %s on %q: %w", method.Address(), n.Name, err)
 					}
 				default:
 					return fmt.Errorf("failed to add address (already exists) %+v to %s: %v", method.Address(), method.Link().Name, err)
@@ -401,7 +409,10 @@ func (n *NetworkInterface) configureInterface(method address.Addressing, link *n
 
 		err = n.rtnlConn.RouteAdd(method.Link(), *r.Destination, gw, rtnl.WithRouteSrc(src), rtnl.WithRouteAttrs(attr))
 		if err != nil {
-			return err
+			// ignore "EEXIST" errors for routes which are already present
+			if opErr, ok := err.(*netlink.OpError); !ok || !os.IsExist(opErr.Err) {
+				return fmt.Errorf("error adding route %s %s on %q: %s", *r.Destination, gw, n.Name, err)
+			}
 		}
 	}
 

pkg/provision/providers/vm/dhcpd.go

@@ -52,7 +52,7 @@ func handler(serverIP net.IP, statePath string) server4.Handler {
 			dhcpv4.WithOption(dhcpv4.OptHostName(match.Hostname)),
 			dhcpv4.WithOption(dhcpv4.OptDNS(match.Nameservers...)),
 			dhcpv4.WithOption(dhcpv4.OptRouter(match.Gateway)),
-			dhcpv4.WithOption(dhcpv4.OptIPAddressLeaseTime(time.Hour)),
+			dhcpv4.WithOption(dhcpv4.OptIPAddressLeaseTime(5*time.Minute)),
 			dhcpv4.WithOption(dhcpv4.OptServerIdentifier(serverIP)),
 		)
 		if err != nil {