In addition to the D2000 KOM and D2000 Archive processes, some other D2000 processes can function as redundant (instance).

Redundancy of the D2000 Event Handler process

The D2000 Event Handler process is started in multiple instances, especially in redundant systems, where it runs on dedicated redundant servers (e.g. in the DMZ for communication with external systems and the web). In this mode:

• The active instance of the D2000 Event Handler process runs ESL and Java scripts.
• After entering the passive state, all scripts are stopped.
• After transitioning to the active state, all scripts are run again.

Redundancy of the D2000 DbManager process

The D2000 DBManager process is started in multiple instances, especially in redundant systems where it runs on dedicated redundant servers (e.g. in the DMZ for communication with external databases). In this mode:

• All requests are directed to the active instance of the D2000 DBManager process.
• After transitioning to the passive state, all ongoing database operations are terminated (ROLLBACK), if the start parameter /DBSH is specified, connections to the database are also closed (recommended).
• After transitioning to the active state, connections to the database are established (if they were previously closed due to the /DBSH startup parameter).

Redundancy of the D2000 SAS process

Usually, the D2000 SAS process is not run in multiple instances, but there can be multiple SAS processes (e.g. Srv1.SAS and Srv2.SAS), especially in redundant systems where the SAS servers run on dedicated redundant servers (e.g. in the DMZ to connect the D2000 HI clients from external networks). In this mode:

• The D2000 HIs are configured to connect to two (or more) SAS servers - ideally with different clients having different orders of IP addresses/server names specified to spread the load across all SAS servers.
• After startup, D2000 SAS creates a connection to an active D2000 Server (HOT).
• After changing the active D2000 Server, D2000 SAS will connect to the new active D2000 Server.
• After a D2000 HI connection to a D2000 SAS process is lost, the D2000 HI may terminate (if it was started with the /S parameter) or try to reconnect as if running in a redundancy group (/RD or /RF parameters).

Redundancy of D2000 OPC Server and D2000 OPC UA Server processes

Usually, the D2000 OPC Server and D2000 OPC UA Server processes are not run in multiple instances, but there can be multiple processes (eg Srv1.OPC and Srv2.OPC for D2000 OPC Server or Srv1.OUS and Srv2.OUS for D2000 OPC UA Server), especially in redundant systems where OPC/OPC UA servers run on dedicated redundant servers (e.g. in DMZ for communication to external systems). In this mode:

• External systems are configured to connect to two (or more) OPC/OPC UA servers - ideally with different clients having different orders of IP addresses/server names specified to spread the load across all OPC/OPC UA servers.
• D2000 OPC Server/D2000 OPC UA Server establishes a connection to an active D2000 Server (HOT) after starting.
• After changing the active D2000 Server, the D2000 OPC Server/D2000 OPC UA Server will connect to the new active D2000 Server.