Introduction

SAP NetWeaver System Landscape Directory (SLD) is a central provider of landscape information in a system landscape. This is key information for many client applications. For many reasons there will be more than just one SLD system in the landscape - for details, read my blog on SLD topology describing how many SLD systems you need and where. I'm asked quite often to comment SLD strategies for customers derived from those recommendations. When it comes to SLD upgrades, however, even if the reasons to upgrade are well accepted, the business downtime caused by the upgrade and more than that the effort to reconfigure all client applications to access the new SLD system often seem too costly. That is why I recommend using a virtual IP address for the SLD in any case, which makes such switches extremely easy and does not influence your business at all.

Using Virtual IP Addresses for Your SLD

The use of a virtual IP address for SLD access is in principle indpendent of the platform and SLD versions used. Special benefits such as the use of a hot-backup SLD will come with SAP NetWeaver 7.1-based realeases, where the full automatic synchronization of SLD systems became available.

(Potential) Benefits of Virtual IP Addresses for Your SLD

Wikipedia defines that "A virtual IP address is an IP address that is not connected to a specific computer or network interface card (NIC) on a computer. Incoming packets are sent to the VIP address, but all packets travel through real network interfaces. VIPs are mostly used for connection redundancy; a VIP address may still be available if a computer or NIC fails because an alternative computer or NIC replies to connections."

This exactly describes it. Once you use a virtual IP address to access SLD systems, you have two benefits:

• You can assign the virtual IP address to another SLD used from then on, without causing any changes on any client system (once all clients use the virtual IP address to access the SLD)
• When there is a switch between two SLDs, the new system can be prepared, then the virtaul IP address is re-assigned, so not gap in the availability of SLD data occurs

Here you see a lanscape setup where a virtual IP address is used for SLD access:

Figure 1: Accessing SLD data using a virtual IP address for data supplier, client applications, and front end access. 

SLD systems used may or may not be in full automatic sync - but full automatic sync really makes this setup very interesting - so releases before the availability was available can use this approach also.

Use Cases for Virtual IP Addresses for Your SLD

These benefits simplify or open the following use cases:

• SLD migration: This can easily be handled - install a new SLD, gather the content from the SLD used so far using the full automatic synchronization, and then re-assign the virtual IP address to the new SLD. This will also work if you only run the 2^nd SLD until the original system is up and running again.
  The same is true, when for example you want to use a standalone SLD as a successor of an SLD running in combination with another application.
• SLD maintenance: During planned downtimes gaps in SLD data availability can be avoided with a hot-backup SLD: Just install an additional SLD system, configure the full automatic synchronization, and re-assign the virtual IP address when needed.

Conclusion & Further Hints

So in practically any scenario where SLD data could be unavailable, using a virtual IP address can solve the problem. Since reserving a virtual IP address should not be too costly, even if at the moment you do not need it, it can come in handy later. It is also possible to implement the use of a virtual IP address in several steps: Once it is available, assign it to your SLD together with the original IP address (both can be used in parallel) and reconfigure all clients one by one for example during normal maintenance.

Note that SLD system you want to address be simply switching the IP address must be running on the same port number.

Related Information

All information on SLD is available in SDN under quick link "nw-sld" http://sdn.sap.com/irj/sdn/nw-sld. This includes the SLD Planning Guide and a blog giving details for SLD topology recommendations, blogs, and demos.