2.3.6 Failover support for launch

You must also plan some sort of failover plan or roll-back plan should you encounter any catastrophic problem during the site launch or go-live.

Recall the two scenarios discussed in the beginning of this chapter. If you are building a new site then any catastrophe will delay your site launch. However, if you are upgrading your site (for High Availability or performance reasons) then this would have a significantly larger impact to your on-going business.

Throughout this book we discuss various techniques to address the latter. One common theme is to decide on a service window of your site that will least impact your user base, and then partially upgrade your site. If your upgrade is not successful for any reason then one alternative is to bring your site up with the remaining capacity and then work in parallel to either troubleshoot the problem or to revert the upgraded capacity back to the previous version or topology of your site.
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