Transport Domain Controller (TDC)

In SAP's Transport Management System (TMS), the Transport Domain Controller (TDC) is the central administration point for managing transport routes and configurations across your entire SAP system landscape. It's the "brain" of your TMS setup.

I. Understanding the Transport Domain Controller (TDC)

1. Central Authority: The TDC holds the master copy of the transport domain configuration, including:
   • List of all SAP systems in the domain.
   • Transport routes (consolidation and delivery).
   • Transport layers.
   • tp global parameters.
   • System attributes (e.g., system type: Development, Quality, Production).
2. Single Point of Configuration: All changes to the TMS landscape configuration (adding systems, modifying routes, adjusting parameters) must be performed exclusively on the TDC.
3. Distribution Mechanism: Once changes are made and saved on the TDC, they are explicitly distributed to all other systems in the transport domain. This ensures consistency across the landscape.
4. RFC Communication: The TDC communicates with other systems in the domain via RFC (Remote Function Call) destinations. A special system user, TMSADM, is automatically created and used for these internal communications.
5. Physical Location: The TDC typically resides on one of your SAP application servers. It's often chosen to be your central Development (DEV) system, as this is where most changes originate.
6. DOMAIN.CFG File: The TDC is responsible for creating and maintaining the DOMAIN.CFG file, which is located in the usr/sap/trans/bin directory of the shared transport directory. This file contains critical information about the transport domain and allows other systems to discover and join it.

II. Prerequisites for Setting up the Domain Controller

Before you begin the setup, ensure the following:

1. Shared Transport Directory:

   • A common, shared network directory, typically usr/sap/trans (Unix/Linux) or \\<hostname>\sapmnt\trans (Windows), accessible from all SAP application servers that will be part of the transport domain.
   • Ensure the directory has appropriate permissions:
     • Full control/read-write access for the <sid>adm user (Unix/Linux) or SAPService<SID> user (Windows) of all SAP systems in the domain.
     • It's common to grant full control to the SAP_LocalAdmin group or a similar group that all SAP service users belong to.
   • Test accessibility: Log on to each SAP system's OS with its respective <sid>adm user and try to create/delete a file in usr/sap/trans.

2. System Client 000: The TMS configuration is always performed in client 000 of the SAP system.

3. User Authorizations: You need a user with full Basis administration authorizations in client 000. DDIC or SAP* are commonly used during initial setup, or a user with the S_CTS_ADMIN authorization profile.

4. Network Connectivity: Ensure all SAP systems can communicate with each other over the network via standard SAP ports (32xx, 33xx) for RFC communication.

III. Detailed Steps for Domain Controller Setup

The setup process for the Domain Controller is initiated directly from the STMS transaction.

1. Log on to the Chosen System for TDC:

   • Identify the SAP system that will serve as your Transport Domain Controller (e.g., your Development system - DEV).
   • Log on to this system in client 000.
   • Use a user with administrative privileges (e.g., DDIC or SAP*).

2. Execute Transaction STMS:

   • In the command field, type STMS and press Enter.

3. Create Transport Domain (Initial Prompt):

   • If TMS has never been configured on this system before (or if DOMAIN.CFG is missing from usr/sap/trans/bin), the system will automatically detect this and present a dialog box.
   • The dialog box will ask: "TMS is not configured. Do you want to create a transport domain?"
   • Click "Yes" (or "Create Transport Domain" button).

4. Automatic Background Activities by TMS:

   Upon your confirmation, TMS will automatically perform several critical configuration steps in the background:

   • Initializes Transport Domain: It sets up the core structures for the new transport domain.
   • Creates Transport Group: A default transport group is created, implicitly linking the initial system to the common transport directory.
   • Creates TMSADM System User:
     • A special system user TMSADM is created in client 000. This user is vital for TMS's internal RFC communication between systems in the domain.
     • TMS automatically generates and manages the password for TMSADM (you don't need to know or change it manually unless explicitly troubleshooting, and even then, let TMS manage it).
   • Generates RFC Destinations:
     • RFC destinations are automatically created in SM59 for internal TMS communication. These usually follow the naming convention TMSADM@<SID>.DOMAIN_<SID>. For example, TMSADM@DEV.DOMAIN_DEV.
     • These RFCs allow the TDC to communicate with itself and, later, with other systems in the domain.
   • Creates DOMAIN.CFG File:
     • This crucial configuration file is generated and placed in the usr/sap/trans/bin directory within your shared transport directory.
     • It contains the domain name, the SID of the domain controller, and other essential TMS parameters. This file is how other SAP systems will discover and join the domain.
   • Sets System Type: The system itself is automatically configured as a "Transport Domain Controller" within its own TMS configuration.

5. Review Initial Configuration:

   • After the automatic setup, STMS will display the "Transport Domain" overview screen.
   • You should see your newly configured Domain Controller system listed.
   • From here, you can click on:
     • Overview -> Systems: To see a list of systems in the domain (initially just your TDC).
     • Overview -> Transport Routes: To see the transport route editor (initially empty).
     • Overview -> Transport Tool: To see global tp parameters.

IV. Important Considerations for the Domain Controller

• Stability and Availability: Choose a stable and highly available system as your TDC. If the TDC is down, you cannot make changes to your transport routes or TMS configuration, and new systems cannot join the domain.
• Performance: The TDC doesn't require exceptional hardware beyond what a typical SAP application server needs, as its primary role is configuration management, not high-volume processing of transports.
• Changing the Domain Controller: While possible, changing the Domain Controller (e.g., if the original TDC is decommissioned) is a more involved process. It requires configuring a "backup domain controller" beforehand or performing a manual "takeover" process.
• Backup Domain Controller: It is highly recommended to configure a Backup Domain Controller. This system will store a copy of the TMS configuration and can take over as the active TDC if the primary one becomes unavailable.
  • To configure: From the active TDC (STMS -> Overview -> Systems), double-click the TDC system, go to the "System Attributes" tab, and enter the SID of the desired backup system in the "Backup" field. Save and distribute the configuration.
• Security of usr/sap/trans: Since DOMAIN.CFG and all transport files reside in this directory, its security is paramount. Restrict write access to only authorized SAP users and administrators.
• No Manual Editing: Never manually edit the DOMAIN.CFG file or the TP_DOMAIN_<SID>.PFL (transport profile) file. TMS manages these files automatically. Manual changes can lead to inconsistencies and transport failures.

By following these steps, you will successfully establish your Transport Domain Controller, laying the foundation for a robust and efficient Transport Management System in your SAP landscape. The next step would be to add other SAP systems to this domain.