Yes! SAP Web Dispatcher High Availability on Premise and Cloud!

More and more customers are asking SUSE how to integrate the SAP Web Dispatcher into the SUSE’s cluster solution. This blog describes step-by-step how to integrate this important SAP software component into pacemaker. The base of the solution is SUSE Linux Enterprise Server for SAP Applications. You can use the solution for any currently supported version of this SUSE product. It is also fine for all hardware architectures supported by SUSE Linux Enterprise Server for SAP Applications and SAP Web Dispatcher.

The Basics to Get Started

The solution combines the following resources into one cluster resource group:

• An IP address used by the clients of the service to connect via network
• A filesystem where the SAP instance Wxx is running
• An SAP instance including the sapwebdisp service

Our best practice guides available at https://documentation.suse.com/ are is already explaining the principle of this cluster solution. The best practices for enqueue-replication for SAP S/4HANA as well as for SAP NetWeaver are describing the integration of SAP central service and replication instances into the cluster. These guides provide useful background information about the cluster stack.

In this blog I assume you have already installed SAP Web Dispatcher and your installation could be controlled by the SAP start-framework using sapstartsrv in the back-end and sapcontrol on the front-end side. If you do not have installed SAP Web Dispatcher please visit this SAP Wiki page. If you already have a SAP Web Dispatcher installation but you do not have it integrated with the
SAP start-framework just have a close look on my blog about generic SAP service intregration into the cluster.

I also assume you have already a file system on a shared drive. The cluster should already be running once we begin to integrate the SAP service.

Both nodes need access to the disk. The cluster will organize that only one of the nodes mounts the file system per time. For the easy IP based setup both nodes are part of the same L2 network. For cloud-based solutions you are using overlay IP addresses, loadbalancer functionality or whatever the hyper-scaler has in his port folio.

Testing the SAP Instance with sapstartsrv and sapcontrol

The software is installed and the start framework is configured. This gives us the chance to use sapcontrol to start or stop the SAP Web Dispatcher instance. And we can get the status of the SAP services included in this SAP instance:

grauenstein01:webadm 52> sapcontrol -nr 00 -function GetProcessList -format script

06.12.2019 16:21:01
GetProcessList
OK
0 name: sapwebdisp
0 description: Web Dispatcher
0 dispstatus: GREEN
0 textstatus: Running
0 starttime: 2019 12 03 18:09:19
0 elapsedtime: 70:11:42
0 pid: 30402

The most important information for now is the SAP service name sapwebdisp. We use this information directly in the next step.

Integration into the Pacemaker Cluster

For the following steps you can use either the graphical web console HAWK or command line tools like the crm shell. This blog focuses on the crm shell. You will be able to adapt the info to HAWK quite easy.

Create a test file like crmWebDisp.txt and include the following lines. Please make sure you adapt the parameters of the resources to your environment.

primitive rsc_fs_<SID>_<INSTNAME> Filesystem \
 params device="<DEVICE>" directory="/usr/sap/<SID>/<INSTNAME>" fstype=xfs \
 op start timeout=60s interval=0 \
 op stop timeout=60s interval=0 \
 op monitor interval=20s timeout=40s
primitive rsc_ip_<SID>_<DEVICE> IPaddr2 \
 params ip=<VIP> \
 op monitor interval=10s timeout=20s
primitive rsc_sap_<SID>_<DEVICE> SAPInstance \
 op monitor interval=11 timeout=60 on-fail=restart \
 params InstanceName=<SID>_<INSTNAME>_<VIRTHOSTNAME> \
 START_PROFILE="/usr/sap/<SID>/SYS/profile/<SID>_<INSTNAME>_<VIRTHOSTNAME>" \
 AUTOMATIC_RECOVER=false MONITOR_SERVICES="sapwebdisp"

group grp_<SID>_<INSTNAME> \
 rsc_ip_<SID>_<INSTANCE> rsc_fs_<SID>_<INSTNAME> rsc_sap_<SID>_<INSTNAME>

The trick is to set the parameter MONITOR_SERVICES correctly. Fill the placeholders in the following way:

Load the resulting crm config file to the cluster:

crm configure load update crmWebDisp.txt

As a result you see the cluster having 4 more resources (one group and 3 primitives). The cluster will immediately start the new resources on one of the cluster nodes.

Getting More Out of the Solution

Now we integrate the SAP start framework using the sap-suse-cluster-connector.

1. Install the package sap-suse-cluster-connetcor (name is written with dashes (“-“) as user root
   zypper in sap-suse-cluster-connector
2. Add the user <sidadm> to the linux user group haclient
   usermod -a -G haclient <sidadm>
3. Adapt the SAP instance profile /usr/sap/<SID>/SYS/profile/<SID>_<INSTNAME>_<VIRTHOSTNAME> and add the following lines:
   service/halib = $(DIR_EXCUTABLE)/saphascriptco.so
   service/halib_cluster_connector = /usr/bin/sap_suse_cluster_connector
4. Kill the sapstartsrv of SAP instance <INSTNAME>
   kill <pid-of-the-sapstartsrv>
5. Wait till sapstartrv is restarted by the cluster
6. Check for the file sapstartsrv.log in the work directory of your instance

If everything is fine you now could stop and start the SAP Web Dispatcher using the sapcontrol command or even the SAP management console without tweaking the cluster.

Enjoy your high available SAP Web Dispatcher! Please also visit our other blogs at #towardsZeroDowntime

This is Fabian Herschel (SUSE) from the SAP LinuxLab.