How the dual stack split killed the HA-scenario

[willi_eimler]

Introduction

The upgrade of our BI 7.01 (ABAP+JAVA Dualstack) was requested by our BW-team. They wanted
to use the new features of NW 7.3. The better integration of the BO tools was
also a benefit of an upgrade. The upgrade was divided into two parts:

Part 1: The Dual Stack Split.

This procedure separates the JAVA stack from the ABAP stack.  Before the dual stack split the JAVA and ABAP runs under one SID. After the split you have two SIDs (the old SID for ABAP and one new SID for JAVA).

Part 2: The Upgrade

This was an usual upgrade.

The Problem

Before the split we had this topology:

After the split and the upgrade the HA features didn't work anymore :sad: In a dualstack system the sap gateway service is addressed by sapgw$$. $$ is substituted by the actual system number.

The following picture shows the topology after the split:

The problem is the Gateway service.  sapgw00 is configured in several destinations, in the UME and the JCO.

It was quite plain to me. The gateway service is HA critical!

A little shame on SAP

This is what you find about "high availability" in the documentation of the Dual stack split:

In the installation documentation of a java stack you find the HA configuration of a "normal" java stack! But what is the difference between a "normal" java stack and a split java stack? It is the UME! In a split java stack the UME is in ABAP!  I'm very glad to know that nobody heard my comments when doing the HA cluster test on our production system!!!

In this picture you see the topology of a HA java stack (found in the installation guide).  But what is to do,  when using the java stack in a BI system with HA? I know somewhere in the paper jungle of SAP you can find something. But sap gives no hint in the standard documentation :sad:

The solution

The following configuration needs to be changed:

1. separate the gateway service
2. logon groups in ABAP
3. the UME Backend Connection
4. JCo RFC-Provider
5. SLD

Separate the gateway service. OSS note 1010990 " Configuring a Standalone Gateway in an HA ASCS instance" explains how to configure the gateway service.

Step 1:
*Do this procedure for each scs.lst of each Instance.

*Changes to the instance-exe-directory. Example for Instance is ASCS00 or DVEBMGS02...
sidadm> cd /usr/sap/<SID>/<Instance>/exe            

*edit the sapcpe config file
sidadm> vi scs.lst    

*add this line to the file      
gwrd                    

Step 2:
*Changes to the profile-directory
sidadm> cdpro                  

*gives you the path <pro_path> of profile-dir.
sidadm> pwd                    

*edit ASCS instance profile
sidadm> vi <pro_path>/<SID>_ASCS<Sys.Nr.>_<hostname>

*add this line to the profile
gw/netstat_once = 0      

Step 3:
*edit the start profile of ASCS

sidadm> vi <pro_path>/START_ASCS<Sys.Nr.>_<hostname>

*Search the first Start_Program_<xx>-entry in the profil, then enter after that line:
_GW=gwrd$(FT_EXE)

*search the Start_Program_<xx>-entry with the highest value of <xx>, then enter:

Start_Program_<xx+1> = local $(DIR_EXECUTABLE)/$(_GW) pf=$(DIR_PROFILE)/<SID>_ASCS<Sys.Nr.>_<hostname> -no_abap

Step 4:
*check in /etc/services the entries:
sapgw<Sys.Nr.>
sapgw<Sys.Nr.>s

restart system

The new gateway service is sapgw<Sys.Nr.> because of the system number of ASCS.

logon groups in ABAP

Logon to the ABAP system and enter transaction SMLT. Configure for each Instance a logon group (in the picture it is PUBLIC)

UME Backend Connection

Comment

You can determine the hostname of

- message server (1)

- gateway server (2)

(1) The name of the Instance Profile of ASCS is <SID>_ASCS<Nr.>_<hostname>

(2) Same hostname as hostname of ASCS

http://<hostname>:50<Sys.Nr. of java>0/nwa

  ->Configuration

  ->Infrastructure

  ->Destinations

JCo RFC-Provider

http://<hostname>:50<Sys.Nr. of java>0/nwa

  ->Configuration

  ->Infrastructure

  ->Destinations

http://<hostname>:50<Sys.Nr. of java>0/nwa

  ->Configuration

  ->Infrastructure

  ->Jco RFC Provider

Login to the ABAP BI system. Go to Transaction SE16 -table-> RSPOR_T_PORTAL

In field RFCDEST you can find the JCo RFC-Destination in ABAP. Go to transaction SM59 and find the RFC destination.

Enter the gateway configuration

SLD

http://<hostname>:50<Sys.Nr. of java>0/sld
  ->Administration
  ->Settings

Logon to ABAP BI system and go to transaction SM59. Enter the gateway configuration (like in RFC destination of JCo) in the following  RFC destinations:

EPILOG

Be aware: You get no hint in the documentation of the dual stack split or the installation about the correct HA settings.

Best regards

Willi Eimler