Red Hat High Availability Clustering for SAP Solutions
After completing this section, you should be able to describe the tiers and components of SAP HANA, SAP S/4HANA, and NetWeaver.
System replication is SAP's recommended configuration for mitigating SAP HANA outage due to planned maintenance, unexpected faults, or disasters. It supports a recovery point objective (RPO) of 0 seconds and a recovery time objective (RTO) that is measured in minutes.
System replication is set up to configure a secondary system as an exact copy of the active primary system, with the same number of active hosts on each site. The number of secondary hosts does not need to be identical. Furthermore, a reliable link is needed between the primary and secondary systems.
Each service of the primary system communicates pairwise with a counterpart in the secondary system. The main difference from the primary system is that the secondary system does not accept requests or queries. The secondary system can accept Read Only (RO) queries only in an Active/Active (Read Enabled) configuration.
The secondary system can be located near the primary system to serve as a rapid failover solution for planned downtime, or to handle storage corruption or other local faults. Alternatively or additionally, a secondary system can be installed in a remote data center for disaster recovery. The instances in the secondary system operate in live replication mode. In this mode, all secondary system services constantly communicate with their primary counterparts; replicate and persist data and logs; and typically load data to memory. The log and data can be compressed before shipping.
After SAP HANA system replication is enabled, each server process on the secondary system establishes a connection with its primary system counterpart, and requests a snapshot of the data. After that time, all logged changes in the primary system are replicated continuously. Whenever logs are persisted (are written to the log volumes of each service) in the primary system, they are also sent to the secondary system.
The following graphic illustrates the general system replication processes:
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To prevent unauthorized access to the SAP HANA database, the internal communication channels between the primary site and the secondary site in a system replication scenario must be protected. This protection might include filtering access to the relevant ports and channels by firewalls, implementing network separation, or applying additional protection at the network level (for example, with a VPN or IPSec). Red Hat recommends routing the connection between the two sites over a special site-to-site high-speed network, which typically already implements security measures such as separation from other network access and encryption or authentication between sites. The details of security measures and implementation of additional network security measures depend on your specific environment.
A transaction in the primary system is not committed before the redo logs are replicated. The selected replication mode makes this determination when setting up system replication.
If the connection to the secondary system is lost or if the secondary system crashes, then the primary system resumes operations, after a brief, configurable timeout. The way that the received logs on the secondary system are handled depends on the selected operation mode. Replication modes and operation modes are covered in more detail later in this course.
While system replication is running, the secondary system is configured identically to the primary system, and is kept on standby until a takeover happens.
In the event of a failure that justifies a full system takeover, you switch the secondary system from the live replication mode to a full operation mode. The secondary system, which already preloaded the same column data as the primary system and possibly is already read enabled, becomes the primary system by replaying the last transaction logs, and then starts to accept both Read and Write queries. When the original system can be restored to service, it can be configured as the new secondary system or be reverted to the original primary configuration as needed.
This takeover process is done manually. However, the Red Hat Enterprise Linux High Availability (HA) solution for SAP HANA is capable of detecting this event. This solution requires a full system takeover, and conducts the entire takeover process automatically. Setup for High Availability is also possible with Ansible. The complete stack of setting up a 2-node RHEL HA solution for SAP HANA is covered in future sections of this course.
Besides the previously mentioned standard setup, in which a primary system ships all the data to the secondary system, you can also configure a multi-tier or a multi-target system replication.
In a multi-tier system replication, a tier 2 system replication setup can act as the source for replication in a chained setup of a primary system, a tier 2 secondary system, and a tier 3 secondary system. The primary system is always on tier 1. The replication source for the tier 2 secondary system is the primary system. The replication source for the tier 3 secondary system is the tier 2 secondary.
In a multi-target system replication, the primary system can replicate data changes to more than one secondary system.
The primary system automatically replicates relevant license information to the secondary system. No additional license needs to be installed, because the primary and secondary system have the same SID. For more information about licensing in SAP HANA system replication, see SAP Note 2211663: https://launchpad.support.sap.com/
When using an Active/Active (read enabled) system replication configuration, the secondary system is subject to licensing.
With the evolution of NetWeaver to SAP S/4HANA (SAP Business Suite 4 SAP HANA), SAP is providing a new product and a next generation of business applications: enterprise software for big data and designed to help you to run in the digital economy.
The SAP S/4HANA family is fully built on the in-memory SAP HANA database platform. Using the advanced potential of SAP HANA, SAP S/4HANA is designed for your digital business, and provides an instant insight by using a single source of truth, real-time processes, dynamic planning, and analysis. With SAP Fiori user experience and a less complex data model, it is designed to run in parallel, while reducing the data footprint of your company. SAP S/4HANA is also already connected to business networks and to company-internal collaboration networks, and is prepared for the Internet of Things. In all these aspects, SAP is protecting your investments by facilitating next-generation business applications.
SAP S/4HANA is composed of the following components:
SAP S/4HANA Enterprise Management: SAP S/4HANA Enterprise Management is designed for enterprises across industries that need a deep and broad level of functions combined with a high degree of flexibility in customization.
SAP S/4HANA Enhanced LoB Functions: SAP S/4HANA Enhanced Line of Business (LoB) Functions enhance the core functions of SAP S/4HANA Enterprise Management to provide additional business benefit for your line of business. You might need a separate license.
SAP S/4HANA Industry-Specific LoB Functions: SAP S/4HANA Industry-Specific LoB Functions enhance the core functions of SAP S/4HANA Enterprise Management to provide industry-specific business benefits for your line of business (LoB). You might need a separate license.
SAP S/4HANA Compatibility Packs: The specific usage rights for SAP S/4HANA Compatibility Packs are set forth in the Software Usage Rights Document. More information can be found here: https://help.sap.com/doc/e2048712f0ab45e791e6d15ba5e20c68/2021/en-US/FSD_OP2021_latest.pdf
The following example architecture consists of SAP S/4HANA:
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Many topics are still to be considered, such as the details of the simplification list for each function and the impact on "add-on" systems, such as analytics. This course focusses on the Red Hat High Availability solution for SAP and automatic setup by using Red Hat Ansible Automation. Nevertheless, understanding what HANA and S/4HANA are from an evolutionary and technical perspective helps to discern how it all fits together.