code: function buildSubnetGroups(numZones = 0) {
    if (numZones < 2) {
      return {};
    }
    return Object.assign(
      {},
      buildRDSSubnetGroup(numZones),
      buildRedshiftSubnetGroup(numZones),
      buildElastiCacheSubnetGroup(numZones),
      buildDAXSubnetGroup(numZones),
    );
  }
docs: Build the database subnet groups
  
  @param {Number} numZones Number of availability zones
  @return {Object}