@@ -15,12 +15,15 @@ import (

 	"github.com/docker/docker/daemon/cluster/convert"

 	executorpkg "github.com/docker/docker/daemon/cluster/executor"

 	clustertypes "github.com/docker/docker/daemon/cluster/provider"

+	"github.com/docker/libnetwork"

 	networktypes "github.com/docker/libnetwork/types"

 	"github.com/docker/swarmkit/agent"

 	"github.com/docker/swarmkit/agent/exec"

 	"github.com/docker/swarmkit/api"

 	"github.com/docker/swarmkit/api/naming"

+	"github.com/docker/swarmkit/log"

 	"github.com/docker/swarmkit/template"

+	"github.com/pkg/errors"

 	"github.com/sirupsen/logrus"

 )

@@ -32,6 +35,14 @@ type executor struct {

 	dependencies  exec.DependencyManager

 	mutex         sync.Mutex // This mutex protects the following node field

 	node          *api.NodeDescription

+

+	// nodeObj holds a copy of the swarmkit Node object from the time of the

+	// last call to executor.Configure. This allows us to discover which

+	// network attachments the node previously had, which further allows us to

+	// determine which, if any, need to be removed. nodeObj is not protected by

+	// a mutex, because it is only written to in the method (Configure) that it

+	// is read from. If that changes, it may need to be guarded.

+	nodeObj *api.Node

 }

 // NewExecutor returns an executor from the docker client.

@@ -157,6 +168,40 @@ func (e *executor) Configure(ctx context.Context, node *api.Node) error {

 		attachments[na.Network.ID] = na.Addresses[0]

 	}

+	// discover which, if any, attachments have been removed.

+	//

+	// we aren't responsible directly for creating these networks. that is

+	// handled indirectly when a container using that network is created.

+	// however, when it comes time to remove the network, none of the relevant

+	// tasks may exist anymore. this means we should go ahead and try to remove

+	// any network we know to no longer be in use.

+

+	// removeAttachments maps the network ID to a boolean. This boolean

+	// indicates whether the attachment in question is totally removed (true),

+	// or has just had its IP changed (false)

+	removeAttachments := make(map[string]bool)

+

+	// the first time we Configure, nodeObj wil be nil, because it will not be

+	// set yet. in that case, skip this check.

+	if e.nodeObj != nil {

+		for _, na := range e.nodeObj.Attachments {

+			// same thing as above, check sanity of the attachments so we don't

+			// get a panic.

+			if na == nil || na.Network == nil || len(na.Addresses) == 0 {

+				logrus.WithField("NetworkAttachment", fmt.Sprintf("%#v", na)).

+					Warnf("skipping nil or malformed node network attachment entry")

+				continue

+			}

+

+			// now, check if the attachment exists and shares the same IP address.

+			if ip, ok := attachments[na.Network.ID]; !ok || na.Addresses[0] != ip {

+				// if the map entry exists, then the network still exists, and the

+				// IP must be what has changed

+				removeAttachments[na.Network.ID] = !ok

+			}

+		}

+	}

+

 	if (ingressNA == nil) && (node.Attachment != nil) && (len(node.Attachment.Addresses) > 0) {

 		ingressNA = node.Attachment

 		attachments[ingressNA.Network.ID] = ingressNA.Addresses[0]

@@ -197,6 +242,42 @@ func (e *executor) Configure(ctx context.Context, node *api.Node) error {

 		return err

 	}

+	var (

+		activeEndpointsError *libnetwork.ActiveEndpointsError

+		errNoSuchNetwork     libnetwork.ErrNoSuchNetwork

+	)

+

+	// now, finally, remove any network LB attachments that we no longer have.

+	for nw, gone := range removeAttachments {

+		err := e.backend.DeleteManagedNetwork(nw)

+		switch {

+		case err == nil:

+			continue

+		case errors.As(err, &activeEndpointsError):

+			// this is the purpose of the boolean in the map. it's literally

+			// just to log an appropriate, informative error. i'm unsure if

+			// this can ever actually occur, but we need to know if it does.

+			if gone {

+				log.G(ctx).Warnf("network %s should be removed, but still has active attachments", nw)

+			} else {

+				log.G(ctx).Warnf(

+					"network %s should have its node LB IP changed, but cannot be removed because of active attachments",

+					nw,

+				)

+			}

+			continue

+		case errors.As(err, &errNoSuchNetwork):

+			// NoSuchNetworkError indicates the network is already gone.

+			continue

+		default:

+			log.G(ctx).Errorf("network %s remove failed: %v", nw, err)

+		}

+	}

+

+	// now update our copy of the node object, reset the attachment store, and

+	// return

+	e.nodeObj = node

+

 	return e.backend.GetAttachmentStore().ResetAttachments(attachments)

 }