<< With the increasingly common use of distributed software components in service-oriented architectures (SOA), it has become essential that the underlying hardware for such applications have a high degree of redundancy. The reason for this is simple: if a hardware platform hosting a critical service fails, the entire enterprise application may be severely degraded, or even fail completely. Currently, the best way to avoid this problem is to implement at least two redundant servers, each running a separate instance of a software service. Depending upon the criticality of the service, more than two copies may need to be running.
Further complicating the situation is the issue of component isolation. Real-world experience with SOA-based applications has proven that while failed hardware will cause components to stop working, the converse is also true. Sometimes software components behave badly and effectively render the hardware useless. We have all seen hung networks and pegged CPUs that were eventually traced to a misbehaving software component. When applications are truly business-critical it is often wise to isolate services onto their own hardware. Finally, transaction volumes and total system loads must be taken into consideration. The larger the expected loads, the more primary and backup hardware that is needed. Designing software services that run in an active-active, load-balancing configuration on separate servers gives us a way to make the "backup" servers help with handling larger system loads. There is a hidden danger in this strategy. If the periodic "high watermark" load presented to the application needs both servers to maintain acceptable performance levels or response times, then we have effectively lost redundancy. This leads to the common strategy of using N+1 servers for each componentN servers to handle the high-watermark load and one additional server to provide coverage for a failure of a server in the "N" pool. The bottom-line: Implementing redundant, isolated hardware in sufficient quantity to cover expected system loads can require a lot of hardware. A typical enterprise data center is proofrows of 1U, 2U, and 4U servers neatly tucked into 7- or 9-foot racks. Fortunately, all of these commodity servers are inexpensivearen't they? Individually, commodity hardware servers are reasonably inexpensive. Adding "one more box" to the enterprise data center, though, involves finding rack space, consideration of power and cooling capacity of the center, adding copper and/or optical data cabling, and adding a KVM port. It further involves provisioning the server with appropriate OS and application software loads, and also generally requires adding a software management agent to the server to enable the server to be monitored from an enterprise systems management console. The ongoing care and feeding of a few dozen servers can stress one systems administrator. What happens when the data center houses hundreds or thousands of servers?>> You can read this at: http://www.adtmag.com/article.aspx?id=18852 Gervas ------------------------ Yahoo! Groups Sponsor --------------------~--> Great things are happening at Yahoo! Groups. See the new email design. http://us.click.yahoo.com/TISQkA/hOaOAA/yQLSAA/NhFolB/TM --------------------------------------------------------------------~-> Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/service-orientated-architecture/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
