The broken link is the result of an Oracle Database Release 11.2 documentation library configuration issue, plus the fact that the High Availability Best Practices book has not been republished recently. The most recently published version of that book (December 2009) is included in the Oracle Database Release 11.1 documentation library, and the links for that specific book are:
We plan to resolve the problem that caused the broken link that you saw, but it may take a while, perhaps depending on when the next revision of the book will be published.
A quick follow-up: The writer currently assigned to the High Availability Best Practices book says that "there is quite a bit of incorrect information in the older book (that is, incorrect for 11.2)," and notes that a Release 11.2 revision is being prepared.
Of course, we cannot guarantee or announce future (planned) publication dates, but be aware that the Release 11.1 book (December 2009) is outdated and incorrect in many instances for Release 11.2, and that a Release 11.2 revision is in progress.