SAP High Availability on AWS: Do You Need Cross-Zone Load Balancing?

Introduction:

In today's fast-paced digital landscape, SAP applications play a vital role in many organizations, serving as the backbone for a wide range of business processes. Ensuring the high availability and reliability of SAP applications on Amazon Web Services (AWS) is essential to guarantee uninterrupted operations and maintain data integrity. In this post, we'll explore the deployment of SAP with high availability on AWS, with a particular focus on utilizing Overlay IP with a Network Load Balancer. Additionally, we'll address the critical question: Is Cross-Zone Load Balancing a necessary component for your SAP deployment?

Overview:

As explained in great detail in our documentation (link), high availability for SAP on AWS requires a robust architectural approach, which involves the use of multiple subnets distributed across different Availability Zones (AZs).

To enable high availability, SAP instances are strategically distributed across various AZs, ensuring that a failure in one AZ doesn't disrupt the entire system. However, it's crucial to have a mechanism to direct incoming traffic to the active SAP instance across different AZs. To achieve this, AWS offers the capability to configure Overlay IP, a fundamental component for this purpose.

Overlay IP enables the use of a non-overlapping private IP address residing outside of the VPC CIDR range to direct SAP traffic to instances across the VPC's Availability Zones. This configuration involves modifying the routing table in AWS to ensure that incoming traffic is directed to the desired SAP instance.

Leveraging Overlay IP with Network Load Balancer:

In the context of SAP high availability, the use of Overlay IP can be combined with a Network Load Balancer (NLB) to efficiently manage incoming traffic. The NLB acts as a pass-through mechanism without SSL termination, ensuring that incoming requests are directed to the Overlay IP address. This combination of Overlay IP and NLB is illustrated in the following architecture.

Cross-Zone Load Balancing: Is It Necessary?

Cross-Zone Load Balancing is a valuable feature of NLBs, designed to distribute traffic across all instances, regardless of their location within the Availability Zones. The main idea is to ensure that incoming requests are effectively routed to applications deployed across multiple AZs.

However, when using Overlay IP with SAP deployments, the target type must be configured as "IP." This configuration causes the NLB to treat the target as existing in "ALL" availability zones. This is because Overlay IP addresses are perceived as residing outside the VPC range. Hence, enabling Cross-Zone Load Balancing is not a necessity in this scenario.

Since routing decisions are made by the route table that determines which Elastic Network Interface (ENI) should receive the traffic, Cross-Zone Load Balancing doesn't provide any benefits in this context. However, it's worth noting that having it enabled doesn't negatively impact the setup either. In scenarios where Overlay IP addresses are used, the route table efficiently guides traffic, making Cross-Zone Load Balancing an optional consideration.

In conclusion, while Cross-Zone Load Balancing is a valuable feature for many AWS deployments, SAP environments using Overlay IP may not require it. With Overlay IP and well-configured route tables, SAP applications can achieve high availability and efficient traffic routing without the need for Cross-Zone Load Balancing. Ultimately, the decision should be based on the specific requirements of your SAP deployment, traffic patterns, and redundancy measures already in place. High availability and robust performance are achievable in SAP environments on AWS with the right architectural choices.