When the only choice for the Input mode of a task parameter is Constant, it means that there is no way for a client to specify a value for the parameter; therefore, the options for specifying User defined value or Choice list are unavailable as input modes. Because the parameter value is a constant, clients can't change it, so it will not become a task parameter when the service is published.
The most common reasons why a task parameter is a constant are discussed below.
Datasets
If the input parameter is for a dataset, it means that the dataset is non-transportable across the Internet. Transportable datasets are features, rasters, tables, or files. Non-transportable datasets are items such as Topologies, TINs, Network datasets, map documents, databases, and so on.
If you publish your task with the Input mode set to Constant, the dataset will be copied to the server (unless the dataset is in the server's data store) for your task to use.
To learn more about non-transportable datasets and suggestions for creating tasks that work with transportable datasets, see the topic Input modes and parameter data types.
Containers
Containers are datasets that contain a mixed collection of other datasets. For example, a folder can contain files, rasters, file geodatabases, and other geodatasets. A file geodatabase is a container of all different kinds of geographic datasets. A map document (.mxd) is a container of layers and all their properties, including references to datasets.
Containers are non-transportable, and the general rule is that the container and all its contents will be copied to the server (unless the container is in the server's data store) and your published task will use the copied container. More information about common container types follows.
Folders
If the input parameter is for a folder, the folder and all files within the folder will be copied to the server (unless the folder is in the server's data store). Only files and geodatasets are copied; no subfolders within the folder are copied. Some geodatasets, such as file geodatabases, rasters, and TINS are technically folders, but they will be copied to the server if found within the folder to be copied.
Map documents
If the input parameter is a map document, the map document, all its layers, and all the datasets referenced by the layers will be copied to the server. If any of the referenced datasets cannot be found in the server's data store, they will be copied to the server as well. Essentially, the map document is packaged, sent to the server, then unpacked on the server.
Geodatabases
If the input parameter is a geodatabase, the geodatabase and all its contents will be copied to the server (unless it's found in the server's data store) and your task will use the copied geodatabase.
Personal geodatabases (.mdb) are not supported on server platforms (64-bit Window and Linux) and will be converted to file geodatabases when copied to the server. Enterprise geodatabases will also be converted to file geodatabases when copied to the server.
Value Tables
Value Tables are used by many tools. They are multicolumn tables such as those illustrated below.
If you need your client to specify their own values rather than using the constant value, you'll need to modify your model or script so that it uses other data types besides Value Table. See Input modes and parameter data types for more information about Value Tables.