The current serve-stale implementation in BIND 9 stores all received
records in the cache for a max-stale-ttl interval (default 12 hours).
This allows DNS operators to turn the serve-stale answers in an event of
large authoritative DNS outage. The caching of the stale answers needs
to be enabled before the outage happens or the feature would be
otherwise useless.
The negative consequence of the default setting is the inevitable
cache-bloat that happens for every and each DNS operator running named.
In this MR, a new configuration option `stale-cache-enable` is
introduced that allows the operators to selectively enable or disable
the serve-stale feature of BIND 9 based on their decision.
The newly introduced option has been disabled by default,
e.g. serve-stale is disabled in the default configuration and has to be
enabled if required.
as "type primary" is preferred over "type master" now, it makes
sense to make "primaries" available as a synonym too.
added a correctness check to ensure "primaries" and "masters"
cannot both be used in the same zone.
these keywords were added to the parser as synonyms for "master"
and "slave" but were never hooked in to the configuration of named,
so they were ignored. this has been fixed and the option is now
checked for correctness.
Originally, the default value for max-stale-ttl was 1 week, which could
and in some scenarios lead to cache exhaustion on a busy resolvers.
Picking the default value will always be juggling between value that's
useful (e.g. keeping the already cached records after they have already
expired and the upstream name servers are down) and not bloating the
cache too much (e.g. keeping everything for a very long time). The new
default reflects what we think is a reasonable to time to react on both
sides (upstream authoritative and downstream recursive).
If "edns-udp-size" is set in a "server" block matching the queried
server, it is accounted for in the process of determining the advertised
UDP buffer size, but its value may still be overridden before the query
is sent. This behavior contradicts the ARM which claims that when set,
the server-specific "edns-udp-size" value is used for all EDNS queries
sent to a given server.
Furthermore, calling dns_peer_getudpsize() with the "udpsize" variable
as an argument makes the code hard to follow as that call may either
update the value of "udpsize" or leave it untouched.
Ensure the code matches the documentation by moving the
dns_peer_getudpsize() call below all other blocks of code potentially
affecting the advertised UDP buffer size, which is where it was located
when server-specific "edns-udp-size" support was first implemented [1].
Improve code readability by calling dns_peer_getudpsize() with a helper
variable instead of "udpsize".
[1] see commit 1c153afce556ff3c687986fb7c4a0b0a7f5e7cd8
The ARM and the manpages have been converted into Sphinx documentation
format.
Sphinx uses reStructuredText as its markup language, and many of its
strengths come from the power and straightforwardness of
reStructuredText and its parsing and translating suite, the Docutils.
