Using a Remote Directory Server - RDS

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# Using a Remote Directory Server - RDS

This section covers the following topics:

- RDS Principles of Operation

- Using a Remote Directory Server

- Creating an RDS Interface

- Creating a Remote Directory Service Routine

- Remote Directory Service Program RDSSCDIR

## RDS Principles of Operation

You have two options to use a service directory:

1. #### Using a service directory in a Natural subprogram.

   Normally, to locate a service, the Natural RPC uses a service directory in a Natural subprogram. This directory is an initialized LDA data structure in program `NATCLTGS` generated by the `SYSRPC` Service Directory Maintenance function and has to be available to every RPC client application.

2. #### Using a remote directory.

   You can use a remote directory to locate a service. A remote directory server (RDS) enables you to define directory definitions in one place so that the RDS's services can be used by all clients in your environment.

This section describes how to use a remote directory server to locate a service.

The remote directory server is implemented as a Natural subprogram.

A sample of such a subprogram is provided in library `SYSRPC`. It is named `RDSSCDIR` and reads the required directory information from a work file. The interface of this subprogram is documented, which enables you to develop your own remote directory service. For more information, see the section Creating an RDS Interface.

The RDS interface is the Natural parameter data area of the Natural subprogram and the directory service routine is the code section of the Natural subprogram. If a remote `CALLNAT` is not found within the client's local service directory, the RPC runtime contacts the remote directory server by executing an internal remote `CALLNAT`.

An internal directory cache minimizes the access to the remote directory. The cache information is controlled by an expiration time which is defined by the remote directory server.

## Using a Remote Directory Server

To use a remote directory server

1. #### Create a Directory File

   Create a directory file for the remote directory service using the Service Directory Maintenance function of the `SYSRPC` utility. The subprogram `RDSSCDIR` is provided in the library SYSRPC and reads the directory information from a Natural work file (fixed-block, record length 80 bytes).

2. #### Start the Remote Directory Server

   Start the remote directory server and proceed with the following steps.

3. #### Define RDS

   You have two options:

   - Specify the RDS in the profile parameter `RDS`.

   - Or use the maintenance function of the `SYSRPC` utility to define remote directory servers (refer to Service Directory Maintenance in the SYSRPC Utility documentation). The definition of remote directory servers is still supported for reasons of compatibility. You should, however, define your RDS in the profile parameter `RDS`. For this purpose, entries are provided that allow to define the location of the directory server. This enables you to expand existing local directory information by one or more remote directory server definitions.

Below is an example of how to define a remote directory server in the service directory `NATCLTGS`.

Service Directory
| NODE | SERVER | LIBRARY | PROGRAM | LOGON
--- | --- | --- | --- | --- | ---
1 | `NODE1` |  |  |  |
2 |  | `SERVER1` |  |  |
3 |  |  | `SYSTEM` |  |
4 |  |  |  | `TESTS1` |
5 |  |  |  | `TESTS2` |
6 | `RDSNODE` |  |  |  |
7 |  | `DIRSRV1` |  |  |
8 |  |  | `#ACI` |  |
9 |  |  |  | `RDSSCDIR` |

This example locally defines a server named `SERVER1`. This server may execute the services `TESTS1` and `TESTS2`.

Additionally, there are definitions for the remote directory server `DIRSRV1`. A remote directory server is identified by a preceding hash (#) sign for the library definition.

The definitions of `NODE` and `SERVER` are used as usual in Natural RPC. The library definition defines the transport protocol (ACI) which has to be used to connect the RDS.

Finally, the `PROGRAM` entry contains the name of the remote subprogram which represents the remote directory service (in this case, it refers to the sample subprogram `RDSSCDIR`).

## Creating an RDS Interface

The RDS interface is the parameter data area (PDA) of a Natural subprogram.

To create your own RDS interface you can use the parameter data area shown below.

    DEFINE DATA PARAMETER
      1 P_UDID(B8)                      /* OUT
      1 P_UDID_EXPIRATION(I4)           /* OUT
      1 P_CURSOR(I4)                    /* INOUT
      1 P_ENTRIES(I4)                   /* IN
      1 P_REQUEST(A16/1:250)            /* IN
      1 P_EXTENT (A16/1:250)            /* OUT
      1 P_RESULT(A32)                   /* OUT
      1 REDEFINE P_RESULT
        2 SRV_NODE(A8)
        2 SRV_NODE_EXT(A8)
        2 SRV_NAME(A8)
        2 SRV_NAME_EXT(A8)
    END-DEFINE

For an explanation of the parameters, refer to the table below.

Parameter | Format/Length | Explanation
--- | --- | ---
`P_UDID` | B8 | Unique directory identifier, should be increased after changing the directory information. The client saves this identifier in its cache. If the binary number increases from one client request to the next, it causes the client to delete its local cache information, because it no longer corresponds to the remote directory information.
`P_UDID_EXPIRATION` | I4 | This defines the expiration time in seconds, that is, the number of seconds during which the client can use its local cache information without connecting the RDS to validate the `UDID` setting. It allows you to define a time limit after which you can be sure that your directory modifications are active for all clients. If you set this time to an unnecessarily low value, you may cause a lot of network traffic to the RDS.
`P_CURSOR` | I4 | The remote procedure call has the option to scan for an alternative server if a connection to the previous one cannot be established, see the profile parameter `TRYALT`. This parameter contains zero for a scan from the top and may be modified by the RDS to remember the record location to continue the scan. The value will not be evaluated by the client, it will only be inserted from the cache to continue scanning.
`P_ENTRIES` | I4 | This parameter contains the number of service definitions in `P_REQUEST`.
`P_REQUEST` | A16/1:250 | A list of services for which a server address can be scanned. An entry is structured as: program name (A8) library name (A8)
`P_EXTENT` | A16/1:250 | Reserved for future use.
`SRV_NODE` | A8 | Contains the server node.
`SRV_NODE_EXT` | A8 | Contains the server node extension.
`SRV_NAME` | A8 | Contains the server name.
`SRV_NAME_EXT` | A8 | Contains the server name extension.

## Creating a Remote Directory Service Routine

The Remote Directory Service Routine is the code area of a Natural subprogram (the default version of this code area is subprogram `RDSSCDIR` in library `SYSRPC`).

To create your own RDS routine

- Modify the pseudo-code documented below.

    Set UDID and UDID_EXPIRATION values
    IF P_ENTRIES = 0
        ESCAPE ROUTINE
    IF P_CURSOR != 0
       position to next server entry after P_CURSOR
       Scan for server which may execute P_REQUEST(*)
    IF found
       SRV_NODE        = found node name
       SRV_NODE_EXT    = node extension
       SRV_NAME        = found server name
       SRV_NAME_EXT    = server extension
       P_CURSOR        = position of found server
    ELSE
       P_CURSOR = 0

## Remote Directory Service Program RDSSCDIR

This program is to be found in library `SYSRPC`. It reads the directory information from a work file (fixed-block, record length 80 byte).

Your program could also read the directory information from elsewhere (from a database, for example).

#### Structure of the Directory Work File

    * comment
    UDID definition
    UDID_EXPIRATION definition
    node definition
    ...
    node definition

#### UDID Definition

    (UDID)
       binary number

#### UDID_EXPIRATION Definition

    (UDID_EXPIRATION)
       number of seconds

#### Node Definition

    (NODE)
       namevalue     (logon-option)
       server definition
       ...
       server definition

#### Server Definition

    (SERVER)
       namevalue     (logon-option)
       library definition
       ...
       library definition

#### Library Definition

    (LIBRARY)
       namevalue
       program definition
       ...
       program definition

#### Program Definition

    (PROGRAM)
       namevalue
       ...
       namevalue

#### Namevalue

    Max. 8 characters in uppercase

The `logon-option` after `namevalue` as well as the following definition lines are optional. For the possible values of `logon-option`, refer to Service Directory Maintenance in the `SYSRPC` utility documentation.

#### Example Directory Read from the Work File:

    (UDID)
    ACB8AAB4777CA000
      (UDID_EXPIRATION)
      3600
      * this is a comment
      (NODE)
      NODE1
             (SERVER)
             SERVER1
                 (LIBRARY)
                 SYSTEM
                      (PROGRAM)
                      TESTS1
                      TESTS2
                      TESTS3
             (SERVER)
             SERVER2   (logon-option)
                   (LIBRARY)
                   SYSTEM
                        (PROGRAM)
                        TESTS4
      (NODE)
      NODE2   (logon-option)
            (SERVER)
            SERVER1
                  (LIBRARY)
                  SYSTEM
                       (PROGRAM)
                       TESTS1
                       TESTS2
                       TESTS3
                       TESTS4

In the above example, the directory contains:

- Two servers `SERVER1` and `SERVER2` running on node `NODE1`.

  The server `SERVER1` may execute the programs `TESTS1`, `TESTS2` and `TESTS3` in library `SYSTEM`.

  The server `SERVER2` may execute the program `TESTS4` on library `SYSTEM`.

- One server `SERVER1` on node `NODE2` which may execute the programs `TESTS1` - `TESTS4` in library `SYSTEM`.

The indentation of the lines in the example above is not required. All lines may start at any position (one). You can modify this file manually or generate it using the `SYSRPC` Service Directory Maintenance function.

### On this page

- RDS Principles of Operation
- Using a Remote Directory Server
- Creating an RDS Interface
- Creating a Remote Directory Service Routine
- Remote Directory Service Program RDSSCDIR