fix(gre-mesh): ensure bridge exists before creating GRE tunnels

src/go/api/experiment/experiment.go

@@ -552,6 +552,26 @@ func Start(ctx context.Context, opts ...StartOption) error {
 			}
 		}
 
+		// Creating experiment bridge after launching VMs to ensure the bridge
+		// already exists in minimega (and OVS) before creating GRE tunnels between
+		// them. This cannot be done as part of the minimega script template since
+		// the VM taps (and thus bridges) do not get created until the overall
+		// minimega namespace is launched.
+		if exp.Spec.UseGREMesh() || exp.Spec.DefaultBridge() != "phenix" {
+			if err := mm.CreateBridge(mm.NS(exp.Metadata.Name), mm.Bridge(exp.Spec.DefaultBridge())); err != nil {
+				if !o.mmErrAsWarn {
+					mm.ClearNamespace(exp.Spec.ExperimentName())
+					return fmt.Errorf("creating experiment bridge: %w", err)
+				}
+
+				if merr, ok := err.(*multierror.Error); ok {
+					notes.AddWarnings(ctx, false, merr.Errors...)
+				} else {
+					notes.AddWarnings(ctx, false, err)
+				}
+			}
+		}
+
 		schedule := make(map[string]string)
 
 		for _, vm := range mm.GetVMInfo(mm.NS(exp.Spec.ExperimentName())) {

src/go/tmpl/templates/minimega_script.tmpl

@@ -18,10 +18,6 @@ ns del-host all
 ns add-host localhost
 {{- end }}
 
-{{- if or (ne .DefaultBridge "phenix") .UseGREMesh }}
-ns bridge {{ .DefaultBridge }} gre
-{{- end }}
-
 {{- $basedir := .BaseDir }}
 
 {{- range .Topology.Nodes }}

src/go/util/mm/minimega.go

@@ -507,6 +507,19 @@ func (Minimega) DisconnectVMInterface(opts ...Option) error {
 	return nil
 }
 
+func (Minimega) CreateBridge(opts ...Option) error {
+	o := NewOptions(opts...)
+
+	cmd := mmcli.NewNamespacedCommand(o.ns)
+	cmd.Command = fmt.Sprintf("ns bridge %s gre", o.bridge)
+
+	if err := mmcli.ErrorResponse(mmcli.Run(cmd)); err != nil {
+		return fmt.Errorf("creating bridge %s with GRE mesh between namespace hosts: %w", o.bridge, err)
+	}
+
+	return nil
+}
+
 func (Minimega) CreateTunnel(opts ...Option) error {
 	host, err := GetVMHost(opts...)
 	if err != nil {

src/go/util/mm/mm.go

@@ -22,6 +22,8 @@ type MM interface {
 	ConnectVMInterface(...Option) error
 	DisconnectVMInterface(...Option) error
 
+	CreateBridge(...Option) error
+
 	CreateTunnel(...Option) error
 	GetTunnels(...Option) []map[string]string
 	CloseTunnel(...Option) error

src/go/util/mm/option.go

@@ -10,11 +10,12 @@ import (
 type Option func(*options)
 
 type options struct {
-	ns   string
-	vm   string
-	cpu  int
-	mem  int
-	disk string
+	ns     string
+	vm     string
+	cpu    int
+	mem    int
+	disk   string
+	bridge string
 
 	injectPart int
 	injects    []string
@@ -73,6 +74,12 @@ func Disk(d string) Option {
 	}
 }
 
+func Bridge(b string) Option {
+	return func(o *options) {
+		o.bridge = b
+	}
+}
+
 func InjectPartition(p int) Option {
 	return func(o *options) {
 		o.injectPart = p

src/go/util/mm/package.go

@@ -60,6 +60,10 @@ func DisconnectVMInterface(opts ...Option) error {
 	return DefaultMM.DisconnectVMInterface(opts...)
 }
 
+func CreateBridge(opts ...Option) error {
+	return DefaultMM.CreateBridge(opts...)
+}
+
 func CreateTunnel(opts ...Option) error {
 	return DefaultMM.CreateTunnel(opts...)
 }