new: [rsync-backup] use key commentary to store backup type

Signed-off-by: Valentin Lab <valentin.lab@kalysto.org>

rsync-backup/hooks/install.d/60-install.sh

@@ -4,16 +4,20 @@
 set -eux
 
 
-[ "${DOMAIN}" ] || {
+[ -n "${DOMAIN}" ] || {
     echo "Error: you must set \$DOMAIN prior to running this script." >&2
     exit 1
 }
 
-[ "${BACKUP_SERVER}" ] || {
+[ -n "${BACKUP_SERVER}" ] || {
     echo "Error: you must set \$BACKUP_SERVER prior to running this script." >&2
     exit 1
 }
 
+KEY_BACKUP_ID=${KEY_BACKUP_ID:-rsync}
+
+KEY_COMMENTARY="$KEY_BACKUP_ID@$DOMAIN"
+
 MIRROR_DIR_PATH="${MIRROR_DIR_PATH:-$PWD/resources/bin/mirror-dir}"
 [ -e "$MIRROR_DIR_PATH" ] || {
     echo "Error: you must set \$MIRROR_DIR_PATH or be the root of the charm to run this script." >&2
@@ -35,8 +39,17 @@ getent passwd rsync >/dev/null ||
 chown rsync:rsync /var/lib/rsync
 
 ## rsync ssh key creation
-[ -e /var/lib/rsync/.ssh/id_rsa ] ||
-    su -c 'ssh-keygen -t rsa -N "" -f ~/.ssh/id_rsa -q -C rsync@'"$DOMAIN" - rsync
+if [ -e /var/lib/rsync/.ssh/id_rsa.pub ]; then
+    ## Mainly for update of old solution
+    content=$(cat /var/lib/rsync/.ssh/id_rsa.pub)
+    commentary=${content##* }
+    if [ "${commentary}" != "$KEY_COMMENTARY" ]; then
+        echo "Updating ssh key commentary from '${commentary}' to '$KEY_COMMENTARY'" >&2
+        sed -ri "s/ [^ ]+\$/ $KEY_COMMENTARY/" /var/lib/rsync/.ssh/id_rsa.pub
+    fi
+else
+    su -c 'ssh-keygen -t rsa -N "" -f ~/.ssh/id_rsa -q -C '"$KEY_COMMENTARY" - rsync
+fi
 
 dest="$BACKUP_SERVER"
 if [[ "$dest" == *"/"* ]]; then