ASCS and SAPGUI Loadbalance

[xymanuel]

Hi there,

i have a problem to understand the behavior of the SAP GUI reagarding ASCS and loadbalancing.

We have the following:

ASCS (messageserver) on SERVER0 SystemNr. 60

Instance1 on SERVER0 SystemNr. 61

Instance2 on SERVER1 SystemNr. 62

In SAP GUI i created a entry and set instancenr. to 60 (Messageserver is running on 60).

I'm able to logon to the system now correctly using the messageserver running on 60.

In services the MS port is maintained like that:

If i now go to properties the SAP GUI tells me that the instancenumber has changed to 62

(which is the Appserver1).

If i press ok, the SAP GUI will change the entry to instancenr. 62.

I think i have a problem now, because from now on my client is only using APPSERVER1 directly to logon and not longer the messageserver??

If im switching which Appserver is contained to the LOGON Group, the GUI switches the Instance Nr. from 61 to 62 and back.

For example only SERVER0 with 61 in the SMLG group, the GUI switches to 61. If i remove SERVER0 from SMLG and

only add SERVER1 with 62, the GUI switches to InstanceNr. 62.

Can somebody tell me what i'm doing wrong? Or why the GUI is acting like this?

Or is the GUI always contacting the messageserver on 3660, nevertheless what is written in the grey "Instance Number" field,

because sapMSSID is set to 3660 in services?

GUI 7.30 PL 10

Regards

Manuel

[Former Member · Accepted solution]

Hi Manuel!

The Group/Server Selection is working like follows:

After specifying the System ID and Message Server SAPGui will first check for an entry sapms<System ID> in \windows\system32\drivers\etc\services.

Then it will connect to the Message Server on the host  you provided in the field "Message Server" and will collect the system configuration. If the connect was successfull it will present all Logon Groups and all Servers belonging to the system.

If you now select a server, your connection will always be opened to this server.

If you select a Logon Group, the Load-Balancing mechanism for that logon group will dynamically select the current logon server via message server for the connect.

Logon Groups are always listed before the servers.

There is one default Logon Group with the installed system: SPACE.

Logon Groups are maintained in transaction SMLG.

The active server within a Logon Group can be shown in SMLG by Goto -> Load Distribution

Logon Group SPACE has no name in SMLG (the name is blank --> SPACE)

(Logon) Group based server selection during login is the only way to ensure that a server is reached in HA configurations when connecting with GUI or RFC-Clients to a HA configured system.

If you select a server in above example, the message server connection is only used to get a list of currently available servers. Your entry in SAPGui is static and will not change if the server is not available. In this case you will not get a connection to the system.

regards

Peter

[xymanuel · Accepted solution]

Hi Peter,

i absolutely understand what you are telling. I also understand SMLG.

The thing is,i am using a logongoup "PUBLIC", but why is the Instancenr. not the port of the messageserver?

Is the "Instancenr" field useless / functionless in SAPGUI if using logongroup?

Why is it filled with 62, if the messageserver is running on 60? (by the loadbalancing mechanism,

yes, but what will happen if the SERVER2 which is running on 62 is not longer available?)

Regards

Manuel

[Former Member · Accepted solution]

The parameters you need for connecting to a message server is:

     message server hostname

     and the SID of the system.

The SID of the system is used to find entry sapmsSID /windows/system32/drivers/etc/services to determine the right port for the service. The service name does not contain any part of the instance number the message server is using.

Hence can use a tcp port of your choise  for sapmsSID with following restrictions:

1. the port must be free on the message server host
2. on all computers where you have programs running which connect to this message server, you have to define the entry sapmsSID in the file /windows/system32/drivers/etc/services

regards

Peter

PS: The instance umber in above screen copy is only informational for a selected server and has no meaning when using logon groups

[xymanuel · Accepted solution]

Peter Simon wrote:


PS: The instance umber in above screen copy is only informational for a selected server and has no meaning when using logon groups

Thats what i want to know. Its only informational. The instancennumber makes no sense if using logongroups.

[Matt_Fraser]

Interesting. I get some different behavior, but I am using different backend releases from you.

I just recently refreshed a sandbox system using the new SWPM, which forced me to split the ASCS off (it wasn't before), so now my PAS is on instance 00 and ASCS on instance 01. It isn't actually load-balanced, so my SAP Logon entry still pointed directly to the PAS instance. However, to test the scenario you described, I went ahead and added a new sapmsSID entry to my workstation's services file (so, sapmsSID 3601/tcp), and created a Group/Server connection in SAP Logon for it.

This is where the behavior is different. I didn't even get a choice for the instance number. I put in the System ID and the Message Server hostname, then I was able to select my logon group, while the Instance Number was greyed out and set to 00 (i.e., to the PAS, not the ASCS).

I saved that and it works fine. It connects me to the PAS on instance 00 when I logon.

What I don't have is multiple dialog instances to actually balance between (it's just a sandbox, after all), so I can't tell if I would get behavior more in line with what you describe if that were the case, with my SAPGUI being 'permanently' connected to just a single app server. I don't think it should work that way. I can't test this in production, where I actually have multiple dialog instances, as currently I still don't have a separated ASCS there (message server and central instance are combined in the old-fashioned way as a single central instance).

My backend is NetWeaver 7.01, so a different release from yours. My SAPGUI is 7.30 pl8 hotfix 1.

You might want to ping the space to see if more answers will come from there (and now I've just done that for you with that link).

Best regards,

Matt