Writeable file already in use

Timothe Litt litt at acm.org
Tue Jan 5 13:29:52 UTC 2016

Jan-Piet Mens <jpmens.dns at gmail.com> wrote:
> This might make you sad if you have lots of zones or large zones.
> .. or even just want to look at what was transferred (whitout having to
> recurse to a `dig axfr').
> I see no reason to omit 'file' (except on a diskless slave 
Or if you care about availability, which is a strong reason for having a
slave in the first place. (Performance is the other.)

If a diskless slave restarts when the master is down, it has no data to
serve.  This will also make you (or your clients) sad, even if you only
have a few small zones :-(    

I agree - don't omit 'file', except on a diskless slave.  Don't try to
share the file, even when it seems to work.  And think twice about why
you have a diskless slave...

The only fault that I find with bind's decision to prohibit shared
writable files is that it took so long to arrive.  Instead of
complaining, which seems to appear here every few months, the response
should be "Thank you - for *finally* preventing this disastrous

I've lost count of how many times I've encountered someone who had
corruption due to this misconfiguration.   There are many (working) ways
to replicate data.  Among them: in-view, dname, external scripts to copy
files, external tools that write records to multiple files, replicators
triggered by file writes (e.g. inotify) or database update triggers ....

Although I remember when a 1MB ("hard") disk was huge - today disk space
is cheap.  Don't trade a few MB (or GB) of space for eventual data
corruption.  And the manpower to implement any of the above is far less
that that spent on recovering from corruption, which can go undetected
for a long time.  [And usually, the folks who run into it haven't tested
their backups...]

As for the "I know I'll never have bind update that zone" - that may be
true today.  But it changes -- perhaps when your successor discovers
it.  Either a tool requires dynamic update, or someone discovers signed
zones, or realizes that dnssec maintain saves a lot of work, or the next
technology comes along.  To misappropriate a K&R quote - "Your constant
is my variable".  Or the ever popular "If you don't take the time to do
it right, you'll have to make the time to do it over...and over again".

Timothe Litt
ACM Distinguished Engineer
This communication may not represent the ACM or my employer's views,
if any, on the matters discussed. 

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