derive peer name from machine id, if possible

This provides a stable peer identity across reboots.

Fixes #901.

weave

@@ -18,6 +18,8 @@ IMAGE_VERSION=${WEAVE_VERSION:-$IMAGE_VERSION}
 MIN_DOCKER_VERSION=1.6.0
 
 # These are needed for remote execs, hence we introduce them here
+MACHINE_ID1=/etc/machine-id
+MACHINE_ID2=/var/lib/dbus/machine-id
 DOCKERHUB_USER=${DOCKERHUB_USER:-weaveworks}
 BASE_EXEC_IMAGE=$DOCKERHUB_USER/weaveexec
 EXEC_IMAGE=$BASE_EXEC_IMAGE:$IMAGE_VERSION
@@ -111,7 +113,7 @@ docker_sock_options() {
 exec_remote() {
     docker $DOCKER_CLIENT_ARGS run --rm --privileged --net=host \
         $(docker_sock_options) \
-        -v /proc:/hostproc \
+        -v /proc:/hostproc -v $MACHINE_ID1:$MACHINE_ID1 -v $MACHINE_ID2:$MACHINE_ID2 \
         -e PROCFS=/hostproc \
         -e DOCKERHUB_USER="$DOCKERHUB_USER" \
         -e WEAVE_VERSION \
@@ -340,6 +342,8 @@ PLUGIN_IMAGE=$BASE_PLUGIN_IMAGE:$IMAGE_VERSION
 PLUGIN_CONTAINER_NAME=weaveplugin
 
 PROCFS=${PROCFS:-/proc}
+[ -z "$MACHINE_ID" -a -f $MACHINE_ID1 ] && MACHINE_ID=$(cat $MACHINE_ID1 2>/dev/null) || true
+[ -z "$MACHINE_ID" -a -f $MACHINE_ID2 ] && MACHINE_ID=$(cat $MACHINE_ID2 2>/dev/null) || true
 DOCKER_BRIDGE=${DOCKER_BRIDGE:-docker0}
 CONTAINER_NAME=${WEAVE_CONTAINER_NAME:-weave}
 BRIDGE=weave
@@ -1508,13 +1512,16 @@ launch_router() {
     enforce_docker_bridge_addr_assign_type
     create_bridge
     docker_bridge_ip
-    # We set the router name to the bridge mac since that is
-    # stable across re-creations of the containers.
-    #
-    # TODO use the mac of one of the physical host interfaces
-    # (eth0, wlan0, etc) so the name becomes stable across host
-    # restarts.
-    PEERNAME=$(cat /sys/class/net/$BRIDGE/address)
+    # Derive the router name from the machine id, if present, since
+    # that is stable across reboots. Otherwise set it to the bridge
+    # MAC since at least that is stable across router re-launches.
+    if [ -n "$MACHINE_ID" ] ; then
+        # first 6 bytes of $MACHINE_ID (which is 16 bytes, represented
+        # as a 32-digit hex string), in MAC notation
+        PEERNAME=$(echo "$MACHINE_ID" | sed 's/\(.\{2\}\)/\1:/g' | cut -c1-17)
+    else
+        PEERNAME=$(cat /sys/class/net/$BRIDGE/address)
+    fi
     # backward compatibility...
     if is_cidr "$1" ; then
         echo "WARNING: $1 parameter ignored; 'weave launch' no longer takes a CIDR as the first parameter" >&2