Which server am I connected to?

Hi Michael,

The concept of primary and standby is different for every Citect process (Alarm Server, Trend Server, Report Server and I/O Servers).
A client could be connected to the primary trend server as well as the standby alarm server. For I/O it's even more complicated because there is no primary or standby server as such. Each I/O device can have a primary and a standby definition, and these can reside on any I/O server in your setup.

If you want to know what I/O server your client is talking to for a specific I/O device, you can use the following function:

sCurrentIOServer = IODeviceInfo(sIODevice, 17); // returns the name of the active I/O server

This syntax only works if your primary and standby I/O devices are configured with the exact same name.
If the names of a redundant I/O device pair are not the same, you first have to find out the I/O device number (aka unit number) before you can find the active server:

iUnitNr = StrToInt(IODeviceInfo(sIODevice, 11)); // returns the I/O device number
sCurrentIOServer = IODeviceInfo(iUnitNr, 17); // returns the name of the active I/O server

To find out which Alarm server you are connected to use:

bConnectedToStandbyServer = StrToInt(ServerInfo("Alarm", 2); // returns 0 if connected to primary server, otherwise 1

This works for Trend and Report servers as well, just replace the word "Alarm" with "Trend" or "Report".

The way I have always thought about this is that one server was doing the bulk of the communications, and the standby was monitoring it. The Alarm server is redundant, with 2 running at the same time, where the Trend and Report have 1 running and one not.
I've worked thorugh this pretty well with the servers. Still having trouble in the I/O.
For example, I would like to read the number of errors from an I/O device.
IODeviceInfo("Device",20,sCluster)
Client side functions (3) work fine, but it seems that the number of errors is a server side function.
MsgRPC should get this, but if it is set as unblocked, it does not return a result and if it is set as blocked, the code trips an error and doesn't complete.
How would you display the number of errors for an IODevice on the graphics?

Hi Michael,

MsgRPC calls can only return information when set to blocking. To be able to display this information, you could run a cicode function on the I/O server that writes the information to a Variable Tag at certain intervals:

FUNCTION MyIODeviceInfoLoop(STRING sIODevice, STRING sTagName)

STRING sActiveServer;

STRING sNumberOfErrors;

WHILE TRUE DO

sActiveServer = IODeviceInfo(sIODevice, 17);

IF ProcessIsServer("IOServer", "", sActiveServer) THEN

// We are the active I/O server for this I/O device

sNumberOfErrors = IODeviceInfo(sIODevice, 20);

TagWrite(sTagName, sNumberOfErrors);

END

SleepMS(1000);  // Update the info every second

END

END

 

You can start this function on both I/O servers using:

TaskNew("MyIODeviceInfoLoop", "^"Device^", ^"DeviceInfoTag^"", 8);

assuming your I/O device is called "Device" and the tag you like to display is called "DeviceInfoTag".

 

Best regards,

Patrick