SAP S/4 HANA - Enqueue Replication 2 High Availability Cluster With Simple Mount #

The following sections focus on background information and the purpose of the document at hand.

1.1 Introduction #

 

SUSE® Linux Enterprise Server for SAP Applications is the optimal platform to run SAP* applications with high availability. Together with a redundant layout of the technical infrastructure, single points of failure can be eliminated.

SAP* Business Suite is a sophisticated application platform for large enterprises and mid-size companies. Many critical business environments require the highest possible SAP* application availability.

The described cluster solution can be used for SAP* SAP S/4HANA ABAP Platform.

SAP S/4HANA ABAP Platform is a common stack of middleware functionality used to support SAP business applications. The SAP Enqueue Replication Server 2 constitutes application level redundancy for one of the most crucial components of the SAP S/4HANA ABAP Platform stack, the enqueue service. An optimal effect of the enqueue replication mechanism can be achieved when combining the application level redundancy with a high availability cluster solution, as provided for example by SUSE Linux Enterprise Server for SAP Applications. Over years of productive operations, the components mentioned have proven their maturity for customers of different sizes and industries.

In contrast to the traditional setups, this setup uses an additional NFS mount for the SAP application layer without the need to have dedicated block devices and cluster-controlled file systems. That greatly simplifies the overall architecture, implementation and maintenance of a SUSE Linux Enterprise High Availability cluster for SAP S/4HANA ABAP Platform with SAP Enqueue Replication Server 2. The here described setup is expected to be default for new deployments on SUSE Linux Enterprise Server for SAP Applications 15.

Figure 1: Certified by SAP #

 

For additional information on the simple mount architecture, also read:

• SUSE blog article "Simple Mount Structure for SAP Application Platform" (https://www.suse.com/c/simple-mount-structure-for-sap-application-platform/).

• SUSE knowledge base TID ("Technical Information Document") 00019944 "Use of Filesystem resource for ASCS/ERS HA setup not possible" (https://www.suse.com/support/kb/doc/?id=000019944).

• Manual page ocf_suse_SAPStartSrv(7), shipped with package sapstartsrv-resource-agents.

The former setup with cluster-controlled file system resources as described in "SAP S/4 HANA - Enqueue Replication 2 High Availability Cluster - Setup Guide" (https://documentation.suse.com/sbp/all/html/SAP_S4HA10_SetupGuide-SLE15) will remain supported.

The document at hand explains how to:

Note

This guide implements the cluster architecture for enqueue replication version 2. For SAP S/4HANA ABAP Platform versions 1909 or newer, enqueue replication version 2 is the default.

This guide focuses on the high availability of the central services. For SAP HANA system replication consult the guides for the performance-optimized or cost-optimized scenario (see Section 1.2, “Additional documentation and resources”).

This document describes setting up a pacemaker cluster using SUSE Linux Enterprise Server for SAP Applications 15 for the Enqueue Replication scenario. The focus is on matching the SAP S/4-HA-CLU 1.0 certification specifications and goals. For the setup described in this document, two or three nodes are used for the ASCS central services instance and ERS replicated enqueue instance. These nodes are controlled by the SUSE Linux Enterprise High Availability cluster. Additional nodes are used for running the database, and the PAS and AAS application server instances. Finally, you need a highly available NFS server.

The goals for the setup include:

The updated certification SAP S/4-HA-CLU 1.0 redefines some of the test procedures and describes new expectations how the cluster should behave in special conditions. These changes allowed to improve the cluster architecture and to design it for easier usage, maintenance procedures and setup.

All shared SAP resources are located on a central NFS server.

Shared disks allow using SBD as the cluster fencing mechanism.

3.1 Differences to previous cluster architectures #

 

• The described architecture now includes the simple mount structure based on an external network file share. Instead of the file system resources needed for each SAP instance, a resource type SAPStartSrv controls the matching sapstartsrv framework process. The cluster configuration is straightforward.

Figure 2: From classic resources to simple mount resources #

 

• For SAP S/4HANA the new concept implies that, after a resource failure, the ASCS does not need to be started at the ERS side. The new enqueue architecture is also named ENSA2.

• Use of native systemd integration for SAP hostagent and instance´s sapstartsrv. Refer to the SAP documentation for the neccessary product version. See also SAP note 3139184. SUSE systemd version 234 at least is needed. For details refer to the SUSE Linux Enterprise Server for SAP Applications product documentation. SUSE resource agents are needed, at least sapstartsrv-resource-agents 0.9.1 and resource-agents 4.x from November 2021.

3.2 Typical systems for ASCS, ERS, database and additional SAP instances #

 

The document on hand describes the installation of a distributed SAP system on three and more systems. In this setup, only two or three systems reside inside the cluster. The database and SAP dialog instances can be controlled by an other cluster. We recommend to install the database on a separate cluster. The cluster configuration for three and more nodes is described at the end of this document. The number of nodes within one cluster should be either two or an odd number.

Note

Because the setup at hand focuses on the SAP S/4-HA-CLU 1.0 certification, the cluster detailed in this guide only manages the SAP instances ASCS and ERS.

If your database is SAP HANA, we recommend setting up the performance-optimized system replication scenario using the automation solution SAPHanaSR. The SAPHanaSR automation should be set up in an own two-node cluster. The setup is described in a separate best practices document available from the SUSE Best Practices documentation Web page at https://documentation.suse.com/en-us/sbp/sap/.

Figure 3: Typical systems for the certification setup #

 

Clustered machines Two-Node scenario #

 

• One machine (valuga11) for ASCS

  • Virtual host name: sapen2as

• One machine (valuga12) for ERS

  • Vortual host name: sapen2er

Optionally clustered machines #

 

• One machine (valuga01) for DB; Virtual host name: sapen2db

• One machine (valuga13) for the PAS; Virtual host name: sapen2d1

• One machine (valuga14) for the AAS; Virtual host name: sapen2d2

3.3 Increasing high availability for the database #

 

Depending on your needs, you can increase the availability of the database if your database is not already highly available by design.

3.3.1 Implementing SAP HANA system replication #

 

A perfect enhancement of the three-node scenario described in this document is to implement an SAP HANA system replication (SR) automation.

Figure 4: One cluster for central services, one for SAP HANA SR #

 

Table 1: The following OS/database combinations are examples for this scenario #

 

SUSE Linux Enterprise Server for SAP Applications 15
Intel X86_64	SAP HANA DATABASE 2.0
IBM PowerLE	SAP HANA DATABASE 2.0

Note

Version for SAP S/4HANA ABAP Platform on Linux on AMD64/Intel 64 and IBM PowerLE. More information about the supported combinations of OS and databases for SAP S/4HANA Server 2021 or newer can be found at the SAP Product Availability Matrix at SAP PAM.

3.4 Integrating SAP S/4HANA into the cluster using the Cluster Connector #

 

The integration of the HA cluster through the SAP control framework using the sap_suse_cluster_connector is of special interest. The service sapstartsrv controls SAP instances since SAP Kernel versions 6.40. One of the classic problems running SAP instances in a highly available environment is the following: If an SAP administrator changes the status (start/stop) of an SAP instance without using the interfaces provided by the cluster software, the cluster framework will detect that as an error status and will bring the SAP instance into the old status by either starting or stopping the SAP instance. This can result in very dangerous situations, if the cluster changes the status of an SAP instance during some SAP maintenance tasks. The new updated solution enables the central component sapstartsrv to report state changes to the cluster software. This avoids dangerous situations as previously described. More details can be found in the blog article "Using sap_vendor_cluster_connector for interaction between cluster framework and sapstartsrv" at https://blogs.sap.com/2014/05/08/using-sapvendorclusterconnector-for-interaction-between-cluster-framework-and-sapstartsrv/comment-page-1/.

Note

If you update from an SAP S/4HANA ABAP Platform version less than 1809, read SAP Note 2641019 carefully to adapt your cluster.

Figure 5: Cluster connector to integrate the cluster with the SAP start framework #

 

Note

For this scenario, an updated version of the sap-suse-cluster-connector is used. It implements the API version 3 for the communication between the cluster framework and the sapstartsrv service.

The new version of the sap-suse-cluster-connector allows starting, stopping and migrating an SAP instance. The integration between the cluster software and the sapstartsrv also implements the option to run checks of the HA setup using either the command line tool sapcontrol or even the SAP management consoles (SAP MMC or SAP MC). Since version 3.1.0 and later the maintenance mode of cluster resources triggered with SAP sapcontrol commands is supported. See also manual page sap_suse_cluster_connector(8).

3.5 Sharing disks and NFS #

 

XFS is used for all local file systems. For /sapmnt/<SID> and /usr/sap/<SID>, NFS is used.

3.5.1 Sharing disk for SBD and mounting NFS for cluster ASCS and ERS #

 

The disk for the fencing mechanism SBD must be shared and assigned to the cluster nodes valuga11 and valuga12 in the two-node cluster example. The NFS file systems for the ASCS and ERS instances are mounted both on valuga11 and valuga12. They could also be mounted on the SAP application servers (in this example valuga13/PAS and valuga14/AAS) to simplify the storage layout of the complete SAP system even more.

Make sure that your shared SBD disk /dev/disk/by-id/SUSE-Example-A is visible on valuga11 and valuga12:

# lsblk | grep /dev/disk/by-id/SUSE-Example-A

During the SAP software installation you need to mount via NFS and entries in /etc/fstab.

3.5.2 Preparing the disk for database and dialog instances (HANA DB) #

 

The disk /dev/disk/by-id/SUSE-Example-B for the database (260 GB) is assigned to valuga01 and formatted with XFS.

You can either use YaST or available command line tools to create the partitions. The following script can be used for non-interactive setups.

Example 1: Create Partitions and File Systems for DB and App Servers on valuga01 #

 

# lsblk
# parted -s /dev/disk/by-id/SUSE-Example-B print
# # we are on the 'correct' drive, right?
# mkfs.xfs /dev/disk/by-id/SUSE-Example-B
# mkdir /hana
# echo "/dev/disk/by-id/SUSE-Example-B /hana xfs defaults 0 2" >> /etc/fstab
# mount /dev/disk/by-id/SUSE-Example-B

Note

D01: Since NetWeaver 7.5 the primary application server instance directory has been renamed to 'D<Instance_Number>'.

NFS server #

 

• 192.168.1.1:/data/export/S4_HA_CLU_10/EN2/sapmnt/EN2 /sapmnt/EN2

• 192.168.1.1:/data/export/S4_HA_CLU_10/EN2/usr/sap/EN2 /usr/sap/EN2

Media #

 

• 192.168.1.1:/sapmedia /sapmedia

192.168.1.100  valuga01
192.168.1.103  valuga11
192.168.1.104  valuga12
192.168.1.105  valuga13

192.168.1.112  sapen2as
192.168.1.113  sapen2er
192.168.1.114  sapen2db
192.168.1.110  sapen2d1
192.168.1.111  sapen2d2

# mkdir -p /sapmnt/EN2 /usr/sap/EN2 /sapmedia
# echo "192.168.1.1:/data/export/S4_HA_CLU_10/EN2/sapmnt/EN2 /sapmnt/EN2 nfs defaults 0 0" >> /etc/fstab
# echo "192.168.1.1:/data/export/S4_HA_CLU_10/EN2/usr/sap/EN2 /usr/sap/EN2 nfs defaults 0 0" >> /etc/fstab
# mount /sapmnt/EN2
# mount /usr/sap/EN2

The overall procedure to install the distributed SAP system is as follows:

The result will be a distributed SAP installation as illustrated here:

Figure 6: Distributed installation of the SAP system #

 

Group sapinst      1001
Group sapsys       1002
Group ha1shm       1003

User  en2adm       2001
User  sapadm       2002
User  ha1adm       2003

# ip a a 192.168.1.112/24 dev eth0
# # if not mounted yet, mount these now
# mount /sapmnt/EN2
# mount /usr/sap/EN2
# cd /sapmedia/SWPM20_P9/
# ./sapinst SAPINST_USE_HOSTNAME=sapen2as

# chown -R en2adm:sapsys /usr/sap/EN2/ASCS00

# ip a a 192.168.1.113/24 dev eth0
# # if not mounted yet, mount these now
# mount /sapmnt/EN2
# mount /usr/sap/EN2
# cd /sapmedia/SWPM20_P9/
# ./sapinst SAPINST_USE_HOSTNAME=sapen2er

# chown -R en2adm:sapsys /usr/sap/EN2/ERS10

# sapcontrol -nr 00 -function Stop    # to stop the ASCS
# sapcontrol -nr 00 -function Start   # to start the ASCS

4.4 Performing subsequent steps for ASCS and ERS #

 

After installation, you can perform several subsequent steps on the ASCS and ERS instances.

4.4.1 Stopping ASCS and ERS #

 

To stop the ASCS and ERS instances, use the commands below. On valuga11, do the following:

# su - en2adm
# sapcontrol -nr 00 -function Stop
# sapcontrol -nr 00 -function StopService

On valuga12, do the following:

# su - en2adm
# sapcontrol -nr 10 -function Stop
# sapcontrol -nr 10 -function StopService

4.4.2 Disabling systemd services of the ASCS and the ERS SAP instance #

 

This is mandatory for giving control over the instance to the HA cluster. See also manual pages ocf_suse_SAPStartSrv(7) and SAPStartSrv_basic_Cluster(7).

# systemctl disable SAPEN2_00.service
# systemctl stop SAPEN2_00.service
# systemctl disable SAPEN2_10.service
# systemctl stop SAPEN2_10.service

Note

Stopping this instance services will stop the SAP instance as well. Starting the instance services will not start the SAP instances.

• Check the SAP systemd integration:

# systemctl list-unit-files | grep SAP
SAPEN2_00.service disabled
SAPEN2_10.service disabled

The instance services are indeed disabled, as required.

# systemctl list-unit-files | grep sap
saphostagent.service enabled
sapinit.service generated
saprouter.service disabled
saptune.service enabled

The mandatory saphostagent service is enabled. This is the installation default. Some more SAP related services might be enabled, for example the recommended saptune.

# cat /usr/sap/sapservices
systemctl --no-ask-password start SAPEN2_00 # sapstartsrv pf=/usr/sap/EN2/SYS/profile/EN2_ASCS00_sapen2as
systemctl --no-ask-password start SAPEN2_10 # sapstartsrv pf=/usr/sap/EN2/SYS/profile/EN2_ERS10_sapen2er

The sapservices file is still there for compatibility. It shows native systemd commands, one per line for each registered instance. You will find a SystemV style example in the appendix.

4.4.3 Integrating the cluster framework using sap-suse-cluster-connector #

 

Install the package sap-suse-cluster-connector version 3.1.0 from the SUSE repositories:

# zypper in sap-suse-cluster-connector

Note

The package sap-suse-cluster-connector contains the version 3.x.x (SAP API 3). The package sap-suse-cluster-connector with version 3.0.x implements the SUSE SAP API version 3. New features like SAP Rolling Kernel Switch (RKS) and migration of ASCS are only supported with this new version. The package`sap-suse-cluster-connector` with version 3.1.x supports in addition the maintenance mode of cluster resources triggered from SAP tools.

For the ERS and ASCS instances, edit the instance profiles EN2_ASCS00_sapen2as and EN2_ERS10_sapen2er in the profile directory /usr/sap/EN2/SYS/profile/.

Tell the sapstartsrv service to load the HA script connector library and to use the connector sap-suse-cluster-connector. On the other hand, make sure the feature Autostart is not used.

service/halib = $(DIR_EXECUTABLE)/saphascriptco.so
service/halib_cluster_connector = /usr/bin/sap_suse_cluster_connector

Add the user en2adm to the Unix user group haclient.

# usermod -a -G haclient en2adm

See also manual pages sap_suse_cluster_connector(8), usermod(8) and groupmod(8).

4.4.4 Adapting SAP profiles to match the SAP S/4-HA-CLU 1.0 certification #

 

For the ASCS instance, change the start command from Restart_Program_xx to Start_Program_xx for the enqueue server (Enqueue Server 2). This change tells the SAP start framework not to self-restart the enqueue process. Such a restart would result in a loss of the locks.

File /usr/sap/EN2/SYS/profile/EN2_ASCS00_sapen2as:

Start_Program_01 = local $(_ENQ) pf=$(_PF)

Optionally, you can limit the number of restarts of services (in the case of ASCS, this limits the restart of the message server).

For the ERS instance, change the start command from Restart_Program_xx to Start_Program_xx for the enqueue replication server (Enqueue Replicator 2).

File /usr/sap/EN2/SYS/profile/EN2_ERS10_sapen2er:

Start_Program_00 = local $(_ENQR) pf=$(_PF) NR=$(SCSID)

4.4.5 Starting ASCS and ERS #

 

To start the ASCS and ERS instances, use the commands below.

On valuga12, do the following

# su - en2adm
# sapcontrol -nr 10 -function StartService EN2
# sapcontrol -nr 10 -function Start

On valuga11, do the following:

# su - en2adm
# sapcontrol -nr 00 -function StartService EN2
# sapcontrol -nr 00 -function Start

# ip a a 192.168.1.114/24 dev eth0
# mount /dev/disk/by-id/SUSE-Example-B /hana
# cd /sapmedia/SWPM20_P9/
# ./sapinst SAPINST_USE_HOSTNAME=sapen2db

# ip a a 192.168.1.110/24 dev eth0
# mount /dev/disk/by-id/SUSE-Example-B-part2 /usr/sap/EN2/D01
# cd /sapmedia/SWPM20_P9/
# ./sapinst SAPINST_USE_HOSTNAME=sapen2d1

# ip a a 192.168.1.111/24 dev eth0
# mount /dev/disk/by-id/SUSE-Example-B-part3 /usr/sap/EN2/D02
# cd /sapmedia/SWPM20_P9/
# ./sapinst SAPINST_USE_HOSTNAME=sapen2d2

# cd /sapmedia/SWPM20_P9/
# ./sapinst

The main procedure to implement the cluster is as follows:

Note

Before you continue to set up the cluster, perform the following actions: First stop all SAP instances. Then remove the (manually added) IP addresses on the cluster nodes. Finally unmount the file systems which will be controlled by the cluster later.

Note

The SBD device/partition needs to be created beforehand. Double-check which device/partition to use! In this setup guide, a disk /dev/disk/by-id/SUSE-Example-A is already reserved for SBD usage.

# modprobe softdog
# echo softdog > /etc/modules-load.d/watchdog.conf
# systemctl restart systemd-modules-load
# lsmod | egrep "(wd|dog|i6|iT|ibm)"

# ha-cluster-init -u -s  /dev/disk/by-id/SUSE-Example-A

# modprobe softdog
# echo softdog > /etc/modules-load.d/watchdog.conf
# systemctl restart systemd-modules-load
# lsmod | egrep "(wd|dog|i6|iT|ibm)"

# ha-cluster-join -c valuga11

Stack: corosync
Current DC: valuga11 (version 1.1.18+20180430.b12c320f5-1.14-b12c320f5) - partition with quorum
Last updated: Mon Jan 28 13:10:37 2019
Last change: Wed Jan 23 09:52:57 2019 by root via cibadmin on valuga11

2 nodes configured
1 resource configured

Online: [ valuga11 valuga12 ]

stonith-sbd	(stonith:external/sbd):	Started valuga11

5.3 Configuring cluster resources #

 

The SAPInstance resource configuration is needed to start and stop the ASCS and the ERS instances themselves. See manual page ocf_heartbeat_SAPInstance(7) for details.

The SAPStartSrv resource starts and stops the sapstartsrv service and guarantees that only one instance is running per cluster at the same time. See manual page ocf_suse_SAPStartSrv(7) for details.

With the new version of ENSA2, the ASCS instance can be started on the same host. There is no longer a need to follow the ERS instance. The ASCS instance receives the enqueue lock table over the network from the ERS instance. If no other node is available, the ASCS instance will be started on the same host where the ERS instance is running.

Figure 7: Resources and constraints #

 

Another benefit of this concept is that you can work with native (mountable) file systems instead of a shared (NFS) file system for the SAP instance directories.

5.3.1 Preparing the cluster for adding the resources #

 

To prevent the cluster from starting partially defined resources, set the cluster to the maintenance mode. This deactivates all monitor actions.

As user root, type the following command:

# crm configure property maintenance-mode="true"

5.3.2 Preparing the new SAPStartSrv resource agent implementation #

 

As a prerequisite for having a single NFS mount for ASCS and ERS, the sapstartsrv instance agents of ASCS and ERS must not be started by the sapinit service during system start-up, as these services are started and stopped by dedicated cluster resources.

With the sapstartsrv-resource-agents RPM package there come two systemd services called sapping and sappong. sapping runs before sapinit and moves /usr/sap/sapservices out of the way. Consequently, the sapstartsrv instance agents are not started automatically by sapinit. sappong runs after sapinit and moves /usr/sap/sapservices back to its original location.

On valuga11 and valuga12, check for the sapstartsrv-resource-agents package and enable the sapping and sappong services.

# zypper info sapstartsrv-resource-agents
# systemctl enable sapping
# systemctl enable sappong

See manual pages ocf_suse_SAPStartSrv(7), sapping(8) and SAPStartSrv_basic_cluster(7) for details.

5.3.3 Configuring resources for the ASCS Instance #

 

First, configure the resources for the IP address, the SAP instance agent and the SAP instance. You need to adapt the parameters for your specific environment.

Make sure that in the SAP instance definition the parameter MINIMAL_PROBE is set to true.

Example 3: ASCS primitive #

 

primitive rsc_ip_EN2_ASCS00 IPaddr2 \
  params ip=192.168.1.112 \
  op monitor interval=10 timeout=20
primitive rsc_SAPStartSrv_EN2_ASCS00 ocf:suse:SAPStartSrv \
  params InstanceName=EN2_ASCS00_sapen2as
primitive rsc_sap_EN2_ASCS00 SAPInstance \
  op monitor interval=11 timeout=60 on-fail=restart \
  params InstanceName=EN2_ASCS00_sapen2as \
     START_PROFILE="/usr/sap/EN2/SYS/profile/EN2_ASCS00_sapen2as" \
     AUTOMATIC_RECOVER=false MINIMAL_PROBE=true \
  meta resource-stickiness=5000

The shown SAPInstance monitor timeout is a trade-off between fast recovery of the ASCS vs. resilience against sporadic temporary NFS issues. You may slightly increase it to fit your infrastructure. Consult your storage or NFS server documentation for appropriate timeout values. Make sure the SAPStartSrv resource has NO monitor operation configured. See also manual pages ocf_heartbeat_SAPInstance(7), ocf_heartbeat_IPaddr2(7) ocf_suse_SAPStartSrv(7) and nfs(5).

Example 4: ASCS group #

 

group grp_EN2_ASCS00 \
  rsc_ip_EN2_ASCS00 rsc_SAPStartSrv_EN2_ASCS00 rsc_sap_EN2_ASCS00 \
  meta resource-stickiness=3000

Create a txt file (like crm_ascs.txt) with your preferred text editor. Add both examples (primitives and group) to that file and load the configuration to the cluster manager configuration.

As user root, type the following command:

# crm configure load update crm_ascs.txt

5.3.4 Configuring resources for the ERS Instance #

 

Next, configure the resources for the IP address, the SAP instance agent and the SAP instance. You need to adapt the parameters for your specific environment.

Make sure that in the SAP instance definition the parameter MINIMAL_PROBE is set to true.

The specific parameter IS_ERS=true must only be set for the ERS instance.

Example 5: ERS primitive #

 

primitive rsc_ip_EN2_ERS10 IPaddr2 \
  params ip=192.168.1.113 \
  op monitor interval=10 timeout=20
primitive rsc_SAPStartSrv_EN2_ERS10 ocf:suse:SAPStartSrv \
  params InstanceName=EN2_ERS10_sapen2er
primitive rsc_sap_EN2_ERS10 SAPInstance \
  op monitor interval=11 timeout=60 on-fail=restart \
  params InstanceName=EN2_ERS10_sapen2er \
     START_PROFILE="/usr/sap/EN2/SYS/profile/EN2_ERS10_sapen2er" \
     AUTOMATIC_RECOVER=false IS_ERS=true MINIMAL_PROBE=true

The shown SAPInstance monitor timeout is a trade-off between fast recovery of the ERS vs. resilience against sporadic temporary NFS issues. You may slightly increase it to fit your infrastructure. Consult your storage or NFS server documentation for appropriate timeout values. Make sure the SAPStartSrv resource has NO monitor operation configured. See also manual pages ocf_heartbeat_SAPInstance(7), ocf_heartbeat_IPaddr2(7) ocf_suse_SAPStartSrv(7) and nfs(5).

Example 6: ERS group #

 

group grp_EN2_ERS10 \
  rsc_ip_EN2_ERS10 rsc_SAPStartSrv_EN2_ERS10 rsc_sap_EN2_ERS10

Create a txt file (like crm_ers.txt) with your preferred text editor. Add both examples (primitives and group) to that file and load the configuration to the cluster manager configuration.

As user root, type the following command:

# crm configure load update crm_ers.txt

5.3.5 Configuring the colocation constraints between ASCS and ERS #

 

Compared to the ENSA1 configuration, the constraints between the ASCS and ERS instances are changed. An ASCS instance should avoid starting up on the cluster node running the ERS instance if any other node is available. Today the ENSA2 setup can resynchronize the lock table over the network.

If the ASCS instance has been started by the cluster on the ERS node, the ERS instance should be moved to another cluster node (col_sap_EN2_no_both). This constraint is needed to ensure that the ERS instance will synchronize the locks again and the cluster is ready for an additional take-over.

Example 7: Location constraint #

 

colocation col_sap_EN2_separate -5000: grp_EN2_ERS10 grp_EN2_ASCS00
order ord_sap_EN2_ascs_first Optional: rsc_sap_EN2_ASCS00:start \
      rsc_sap_EN2_ERS10:stop symmetrical=false

Create a txt file (like crm_col.txt) with a text editor. Add both constraints to that file and load the configuration to the cluster manager configuration.

As user root, type the following command:

# crm configure load update crm_col.txt

5.3.6 Activating the cluster #

 

The last step is to end the cluster maintenance mode and to allow the cluster to detect already running resources.

As user root, type the following command:

# crm configure property maintenance-mode="false"

Multi-node cluster setups mean cluster configurations with more than two nodes. Depending on the starting point it is possible to extend a two-node cluster setup or directly start with more than two nodes for an ASCS / ERS high availability setup. The examples below will show the setting up of multi-node cluster and the extension of an existing two node cluster pair. The major configuration changes will be shown and the basic preparation of the new cluster member node.

The task list to set up the three node cluster is similar to the task list for the two-node cluster. However some details are described different here to get a diskless SBD setup. Such a diskless SBD setup is an optional improvement for three nodes, but does not work for two nodes. On the other hand, priority fencing is an optional improvement for two nodes, but does not work for three nodes. An example priority fencing configuration for the two-node cluster is shown in the appendix. See the SUSE Linux Enterprise High Availability product documentation for details (https://documentation.suse.com/sle-ha/15-SP3/single-html/SLE-HA-administration/#pro-ha-storage-protect-fencing).

Note

When extending a cluster from two to three nodes, make sure to not use priority fencing.

7.1 Extending an existing two-node cluster configuration #

 

Tasks #

 

1. Backing up the current cluster

2. Installing the operating system of the new node

3. Patching the existing nodes

4. Preparing the new node’s operating system

5. Installing the cluster software on the new node

6. Preparing SAPStartSrv resource agent on the new node

7. Preparing the SAP installation on the new node

8. Adding the new node to the cluster

9. Testing the new cluster configuration

7.1.1 Backing up the current cluster #

 

To back up the current cluster, perform a

• Backup of your system including

  • cluster configuration

  • corosync.conf

  • all data and configuration which are important and customized and not default

The system is configured as described in the SUSE Best Practices document SAP S/4 HANA - Enqueue Replication 2 High Availability Cluster With Simple Mount - Setup Guide.

To back up the cluster configuration, go to one of the cluster nodes and safe the cluster configuration with crm and crm report commands:

# crm configure save 2node.txt

Back up the existing /etc/corosync/corosync.conf and all other files which may be important for a restore. This example is one method creating a backup. The important point is using an external destination.

# tar cvf /<path to an external storage>/bck_2nodes_configuration.tar \
      /etc/corosync/corosync.conf \
      2node.txt \
      <add your additional files here>

7.1.2 Installing the operating system of the new node #

 

We recommend using automating the installation to ensure that the system setup across nodes is identical. Make sure to document any additional steps you take beyond the automated setup. In our example, we deploy our machines with an AutoYaST configuration file and run a post step script which does the basic configuration.

7.1.3 Patching the existing nodes #

 

If applicable, install the latest updates and patches on your existing nodes. Alternatively, if you are using frozen repositories such as those provided by SUSE Manager, add the new system to the same repositories, so they have the same patch level as your existing nodes.

Use zypper patch or zypper update depending on your company’s rules.

• We recommend installing the latest available patches to guarantee system stability and hardening. Bug fixing and security patches help avoid unplanned outages and make the system less vulnerable.

There are multiple ways:

# zypper patch
## or
# zypper update

7.1.4 Preparing the new node’s operating system #

 

Example 8: Check for valid DNS, time synchronization, network settings #

 

• Verify that DNS is working:

  # ping <hostname>

• Set up chrony (this is best done with yast2) and enable it:

  # yast ntp-client

• Check the network settings:

  # ip r

You may run into trouble if there is no valid or no default route configured.

• Patch the new system like the existing nodes, verify that your systems have the same patch level and that all required reboots have been performed.

7.1.5 Installing cluster software on the new node #

 

Example 9: Installing packages #

 

• Install the pattern ha_sles on the new cluster node:

  # zypper in -t pattern ha_sles

• Install the package sap-suse-cluster-connector version 3.1.0 from the SUSE repositories:

  # zypper in sap-suse-cluster-connector

7.1.6 Preparing SAPStartSrv resource agent on the new node #

 

• Install the sapstartsrv-resource-agents package and enable the sapping and sappong services.

  # zypper in sapstartsrv-resource-agents
  # systemctl enable sapping
  # systemctl enable sappong

After installing all necessary packages, compare installed package versions.

Example 10: Check that all nodes have the same software packages and versions: #

 

• On the existing cluster nodes, type:

  # rpm -qa | sort >rpm_valuga11.log

• On the new node, type:

  # rpm -qa | sort >rpm_valuga13.log

• Copy the file from one node to the other and compare the two versions:

  # vimdiff rpm_valuga13.log rpm_valuga11.log

Note

If there any differences fix them first before you proceed.

Example 11: Install and configure the watchdog device on the new machine. #

 

Instead of deploying the software-based solution, preferably use a hardware-based watchdog device. The following example uses the software device but can be easily adapted to the hardware device.

# modprobe softdog
# echo softdog > /etc/modules-load.d/watchdog.conf
# systemctl restart systemd-modules-load
# lsmod | egrep "(wd|dog|i6|iT|ibm)"

Note

Ensure that the new node is connected to the same SBD disk connected to the existing two nodes. Ensure that the new node has the same exact SBD configurations already exist on the two existing nodes

# sbd -d /dev/disk/by-id/SUSE-Example-A dump

7.1.7 Preparing the SAP installation on the new node #

 

With SWPM 2.0 (SP4 or later), which is part of the SL Toolset, SAP provides a new option which can perform all necessary steps to prepare a fresh install server to be able to fit into an existing SAP system. This new option will help us to prepare a new host which can later run either the ASCS or ERS in the cluster environment.

You need to create the directory structure that should run the SAP resource. The instance directory is located on an NFS share for all nodes.

• Create mount points and mount NFS shares on the new added node (valuga13):

Example 12: Mount NFS Shares on valuga13 #

 

# mkdir -p /sapmnt/EN2 /usr/sap/EN2 /sapmedia
# mount -t nfs 192.168.1.1:/data/export/S4_HA_CLU_10/EN2/sapmnt/EN2    /sapmnt/EN2
# mount -t nfs 192.168.1.1:/data/export/S4_HA_CLU_10/EN2/usr/sap/EN2    /usr/sap/EN2
# mount -t nfs 192.168.1.1:/sapmedia /sapmedia

As the directories /sapmnt/EN2, /usr/sap/EN2 need to be available at all time, make sure they are mounted during boot. This can be achieved by putting the information into the /etc/fstab.

The next step requires the following information:

• profile directory

• password for SAP System Administrator

• UID for sapadm

# cd /sapmedia/SWPM20_P9/
# ./sapinst

• SWPM product installation path:

  • Installing SAP S/4HANA Server 2021 → SAP HANA DATABASE → Installation → Application Server ABAP → High-Availability System → Prepare Additional Cluster Node

• Use /sapmnt/EN2/profile for the profile directory

• All passwords: <use-your-secure-pwd>

• UID for sapadm: 2002

Example 13: Post Step Procedure after SAP Preparation Step #

 

• Add the user en2adm to the unix user group haclient.

  # usermod -a -G haclient en2adm

• Register the ASCS and the ERS SAP instance:

  # LD_LIBRARY_PATH=/usr/sap/hostctrl/exe:$LD_LIBRARY_PATH; export LD_LIBRARY_PATH
  # /usr/sap/hostctrl/exe/sapstartsrv pf=/usr/sap/<SID>/SYS/profile/<SID>_ERS<instanceNumberErs>_<virtHostNameErs> -reg
  # /usr/sap/hostctrl/exe/sapstartsrv pf=/usr/sap/<SID>/SYS/profile/<SID>_ASCS<instanceNumberAscs>_<virtHostNameAscs> -reg

  

  Note

  This must be done for each instance. Call sapstartsrv with parameters pf=<profile-of-the-sap-instance> and -reg.

• Disable systemd services of the ASCS and the ERS SAP instance:

  # systemctl disable SAPEN2_00.service
  # systemctl disable SAPEN2_10.service

  

  Note

  This is mandatory for giving control over the instance to the HA cluster.

• Check the SAP systemd integration:

  # systemctl list-unit-files | grep sap
  saphostagent.service enabled
  sapinit.service generated
  saprouter.service disabled
  saptune.service enabled
  # systemctl list-unit-files | grep SAP
  SAPEN2_10.service disabled
  SAPEN2_10.service disabled
  # cat /usr/sap/sapservices
  systemctl --no-ask-password start SAPEN2_00 # sapstartsrv pf=/usr/sap/EN2/SYS/profile/EN2_ASCS00_sapen2as
  systemctl --no-ask-password start SAPEN2_10 # sapstartsrv pf=/usr/sap/EN2/SYS/profile/EN2_ERS10_sapen2er

7.1.8 Adding the new node to the cluster #

 

Example 14: Adding the New Node to the Cluster #

 

Check if the SBD device is available in case the SBD stonith method is in place for the two nodes. If the existing cluster using a different, supported stonith mechanism check and verify them too for the new cluster node.

# sbd -d /dev/disk/by-id/SUSE-Example-A dump

• Joining the cluster can be done with ha-cluster-join:

# ha-cluster-join -c valuga11

After the new node has joined the cluster, the configuration must be adapted to the new situation. Double-check if joining the cluster was successful and verify the file /etc/corosync/corosync.conf.

# awk '/quorum/,/}/' /etc/corosync/corosync.conf
# corosync-quorumtool -s

The values expected_votes and two_node should now look like this on all nodes:

expected_votes: 3
two_node: 0

Modify the cluster configuration and set a new colocation rule with crm:

# crm configure delete col_sap_EN2_no_both
# crm configure colocation ASCS00_ERS10_separated_EN2 -5000: grp_EN2_ERS10 grp_EN2_ASCS00

7.1.9 Testing the new cluster configuration #

 

It is highly recommended to run certain test to verify that the new configuration is working as expected. A list of test can be found in the basic setup for the two node cluster above.

For more information, see the documents listed below.

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