code: @Override
      public ReservedCacheNode purchaseReservedCacheNodesOffering(PurchaseReservedCacheNodesOfferingRequest request) {
          request = beforeClientExecution(request);
          return executePurchaseReservedCacheNodesOffering(request);
      }
docs: <p>
  Allows you to purchase a reserved cache node offering.
  </p>
  
  @param purchaseReservedCacheNodesOfferingRequest
  Represents the input of a <code>PurchaseReservedCacheNodesOffering</code> operation.
  @return Result of the PurchaseReservedCacheNodesOffering operation returned by the service.
  @throws ReservedCacheNodesOfferingNotFoundException
  The requested cache node offering does not exist.
  @throws ReservedCacheNodeAlreadyExistsException
  You already have a reservation with the given identifier.
  @throws ReservedCacheNodeQuotaExceededException
  The request cannot be processed because it would exceed the user's cache node quota.
  @throws InvalidParameterValueException
  The value for a parameter is invalid.
  @throws InvalidParameterCombinationException
  Two or more incompatible parameters were specified.
  @sample AmazonElastiCache.PurchaseReservedCacheNodesOffering
  @see <a href="http://docs.aws.amazon.com/goto/WebAPI/elasticache-2015-02-02/PurchaseReservedCacheNodesOffering"
  target="_top">AWS API Documentation</a>