Add a default value for BACKUP_ARCHIVE.

backup.sh

@@ -61,7 +61,7 @@ if [ ! -z "$AWS_S3_BUCKET_NAME" ]; then
   TIME_UPLOADED="$(date +%s.%N)"
 fi
 
-if [ ! -z "$BACKUP_ARCHIVE" ]; then
+if [ -d "$BACKUP_ARCHIVE" ]; then
   info "Archiving backup"
   mv -v "$BACKUP_FILENAME" "$BACKUP_ARCHIVE/$BACKUP_FILENAME"
 fi

entrypoint.sh

@@ -9,7 +9,7 @@ BACKUP_SOURCES="${BACKUP_SOURCES:-/backup}"
 BACKUP_CRON_EXPRESSION="${BACKUP_CRON_EXPRESSION:-@daily}"
 AWS_S3_BUCKET_NAME="${AWS_S3_BUCKET_NAME:-}"
 BACKUP_FILENAME="$(date +"${BACKUP_FILENAME:-backup-%F.tar.gz}")"
-BACKUP_ARCHIVE="${BACKUP_ARCHIVE}"
+BACKUP_ARCHIVE="${BACKUP_ARCHIVE:-/archive}"
 BACKUP_WAIT_SECONDS="${BACKUP_WAIT_SECONDS:-0}"
 BACKUP_HOSTNAME="${BACKUP_HOSTNAME:-$(hostname)}"
 DOCKER_STOP_OPT_IN_LABEL="${DOCKER_STOP_OPT_IN_LABEL:-docker-volume-backup.stop-during-backup}"