[bind10-dev] document zonemgr configurations

[Jeremy C. Reed]

Please help provide some succinct explanations for the the zonemgr 
configurations. Any clarifications would be appreciated.

       lowerbound_refresh defines the minimum SOA REFRESH time in 
seconds. The default is 10.

* From my tests this lowerbound is set before the jitter is used. Is 
that fine? Or should this force the lowerbound regardless of the 
jitter?

       lowerbound_retry defines the minimum SOA RETRY time in seconds. 
The default is 5.

       refresh_jitter is used to provide a time range for randomizing 
the refresh and retry timers to help avoid many zones needing to do a 
refresh or retry at the same time. This value is a real number. The 
maximum amount is 0.5 (the new timer will be within half the original 
time). The default is 0.25 (up to a quarter sooner). Set to 0 to disable 
the jitter.

*** If the SOA REFRESH is one week then the actual SOA check may happen 
as soon as 5.25 days. I guess that is okay.

       reload_jitter
       This value is a real number. The default is 0.75.

* What is this reload_jitter? Why is the default 0.75? I attempted to 
read the code several times. Why is it called "reload"?  Why doesn't it 
have a maximum? Can it be disabled?

       max_transfer_timeout defines the maximum amount of time in 
seconds for a transfer.  The default is 14400 (4 hours).

* Why "transfer"? Isn't this a timeout for doing the refresh (SOA 
lookup)? I set to zero and still worked -- according to code the timeout 
is set to the current time; it did cause 83 ZONEMGR_REFRESH_ZONE lines 
to be logged (for a single refresh) but it appeared to work (it got my 
updated zone). Why four hour default?

       secondary_zones is a list of slave zones that the b10-zonemgr 
should keep timers for. The list items include the name (which defines 
the zone name) and the class (which defaults to "IN").

* Note: the longer examples are in my guide (needs to be committed).

       (A deprecated configuration is jitter_scope which is superceded 
by refresh_jitter and reload_jitter.)