At the tail end of our certification process at SAP, Citrix engaged in a unique opportunity to make use of the SAP APIs, using Workflow Studio to auto-configure the Citrix NetScaler for Load Balancing. The way it works is, Workflow Studio polls the SAP API, reads the response, and then based on the results in the response, configures the NetScaler Load Balancing groups that map directly to the SAP servers running in the server farm.
SAP has a community group dedicated to the development of their APIs, please reference the latest blog post Catching Up with Deployment and Operations Automation, describes the SAP APIs.
The SAP Community Definition Group (CDG) – titled “PCDG 97 NetWeaver Infrastructure APIs for Network Solutions” – is focused on automation of network-application integrated configuration and operation. As the group title implies, the SAP NetWeaver technology platform includes APIs, which are used by the NetScaler ADCs (load balancers) to auto-configure themselves as proxies for multi-instance SAP application systems. Using Citrix Workflow Studio, the SAP APIs are polled on a regular basis so that the NetScaler ADCs can react to SAP application instance changes during production runtime.
If another application instance is brought up, let’s say for providing more computing capacity for an increasing end-user load, or if an instance is brought down temporarily for maintenance, Workflow Studio communicates with the NetScaler ADC to adjust load balancing automatically without any manual administrator intervention. There is no more wait, or lengthy change management required to provision applications.
Workflow Studio, NetScaler and SAP API Use Cases:
Use Case 1: (auto-configure new SAP services).
Workflow Studio sends a URL request to the SAP Message Server, and receives a response. Workflow Studio parse’s the response, looking for specific SAP generated patterns. WFS then uses this information to configure a Load Balancing Virtual Server inside of the Citrix NetScaler.
Use Case 2: (dynamic configuration).
Workflow Studio repeatedly queries the SAP API. WFS studio can determine hostnames, ip addresses, port numbers, and whether an SAP server is coming online or going down. When a SAP server comes online/goes down – WFS detects this change, and then takes action on the Citrix NetScaler, to add/remove the SAP service from the Load Balancing group – automatically.
Use Case 3: (graceful shutdown).
Workflow Studio queries the SAP API, determines a SAP server is going down, and based on the response, waits until all existing sessions have been retired, before removing the server from the Load Balancing group . During the shutdown period, no new sessions are added to that SAP server, providing a graceful shutdown of the SAP service. This way, there are no TCP resets sent to existing sessions. New logins are routed to a different server.