code: function createBackupFile(sourceUrl, backupTmpFilePath) {
    return new Promise((resolve, reject) => {
      couchbackup.backup(
        sourceUrl,
        fs.createWriteStream(backupTmpFilePath),
        (err) => {
          if (err) {
            return reject(new VError(err, 'CouchBackup process failed'));
          }
          debug('couchbackup to file done; uploading to S3');
          resolve('creating backup file complete');
        }
      );
    });
  }
docs: Use couchbackup to create a backup of the specified database to a file path.
  
  @param {any} sourceUrl Database URL
  @param {any} backupTmpFilePath Path to write file
  @returns Promise