Fix MetalLB L2Advertisement to use baremetal network interface only

Author: zhfeng

ci-operator/step-registry/hypershift/kubevirt/baremetalds/metallb/hypershift-kubevirt-baremetalds-metallb-commands.sh

@@ -5,6 +5,22 @@ set -o errexit
 set -o pipefail
 set -x
 
+POOL_RANGE="192.168.111.30-192.168.111.50"
+POOL_ADDRESS="${POOL_RANGE%%-*}"
+
+# Determine which network interface routes to the IP pool subnet so that
+# L2 announcements are only sent on the baremetal network interface.
+# Without this, extra network interfaces (e.g. from nmstate) can cause
+# MetalLB speakers to fail to announce VIPs.
+NODE_NAME=$(oc get nodes -o jsonpath='{.items[0].metadata.name}')
+METALLB_IFACE=$(oc debug "node/${NODE_NAME}" -- chroot /host ip route get "$POOL_ADDRESS" 2>/dev/null \
+  | grep -oE 'dev [^ ]+' | head -1 | awk '{print $2}')
+if [[ -z "$METALLB_IFACE" ]]; then
+  echo "WARNING: Could not determine MetalLB interface, defaulting to enp1s0"
+  METALLB_IFACE="enp1s0"
+fi
+echo "Using interface $METALLB_IFACE for MetalLB L2 announcements"
+
 oc create -f - <<EOF
 apiVersion: metallb.io/v1beta1
 kind: MetalLB
@@ -21,7 +37,7 @@ metadata:
   namespace: metallb-system
 spec:
   addresses:
-  - 192.168.111.30-192.168.111.50
+  - ${POOL_RANGE}
 EOF
 
 oc create -f - <<EOF
@@ -33,4 +49,6 @@ metadata:
 spec:
   ipAddressPools:
    - metallb
+  interfaces:
+   - ${METALLB_IFACE}
 EOF