multi-master with mysql backend
wllarso.dns at gmail.com
Mon Feb 14 15:39:37 UTC 2011
On Feb 13, 2011, at 9:06 AM, fddi wrote:
> I do not know why you really don't liket this mysql solution.
> OK I am talking of a DNS for HA purposes for grid computing services
> for exampe, so DNS
> resolution must be always working at any cost.
> The David solution can be OK, but I want to be sure not to have
> issues with serial numbers on the two servers
> and the mysql solution looks safer to me. You do not have to rsync
> anything, just have mysql properly configured.
This list is read by many people with extreme experience with DNS and
DNS operations. Using the information that you have provided, many
solutions have been provided to meet the requirements that you have
stated. I would suggest that you at least consider this other
solutions and not be as adamant about using your proposed MySQL
You state that you have a "HA" requirement. Please understand that
this is not an uncommon requirement for a DNS operation. In fact,
almost all DNS operations have this same requirement. Just imagine if
the root servers did not have a require for "high availability". The
same goes for the "com", "net", "org" servers ("it" also). This is
not an unusual requirement and a standard BIND DNS server provides
this very well.
Now, I would also suggest that a MySQL DNS server may not be the best
solution for a critical DNS operation. Please take a look at the
benchmark work done comparing BIND using various backend systems,
including MySQL. This can be found at http://bind-dlz.sourceforge.net/perf_tests.html
, which is part of the work that the people that developed DLZ for
BIND. The standard BIND server could provide 16,000 queries per
second. The same BIND server using a MySQL backend could handle less
than 700 qps.
BIND DLZ using MySQL is NOT what I would consider to be a high
performance solution for a DNS operation. Now, granted, these results
were not using a "current" version of BIND, nor was this being run on
any "high power" hardware. Performance of BIND DLZ using a MySQL
backend may have easily been improved, but so has the performance of
the base system too. A 20 to 1 performance advantage for a straight
BIND solution will be hard to overcome.
So, performance isn't something that a MySQL backend provides to a DNS
operation and high availability is something that all DNS server do
provide, so your real requirement must be something else, such as
being able to update multiple servers at the same time. But Doug
Barton has identified that using "nsupdate" to update both (all)
servers also provides a solution to meet this requirement.
So, your "the mysql solution looks safer to me", may be your viewpoint
which is not universally agreed upon. You also have stated "just have
mysql properly configured". This statement is not unique to MySQL but
to BIND also. BIND also needs to be properly configured, no different
than with MySQL - nothing unique here.
Now, my single belief for any DNS operation is to follow the KISS
principle, "keep it simple, stupid". A less complex system will be
more reliable than a more complex system, because of having less
potential points of failure. This reliability is the single most
important requirement for a DNS operation. A DNS operation that
requires running both BIND and MySQL will be inherently less reliable
than one running just BIND.
The complexity of a MySQL BIND server makes for a less reliable system
than one just using BIND. The performance of a MySQL based BIND
server is much less than a standard BIND server. Managing DNS
information using dynamic DNS provides a simple solution to updating
the zone information. So, what is the actual advantage of using a
MySQL backend to BIND? I'm not convinced that there is any advantage
and I am sure that there are many downsides to using this.
Using MySQL for a backend to BIND is a fairly commonly proposed
solution but it's actual implementation is not followed up on. I
looked at using MySQL, but the performance limitations were an
absolute deal killer. I set up a simple BIND/MySQL system and
benchmarked it and duplicated the performance trends from the BIND-DLZ
developers. Maybe this has been improved, but these results have not
be published so we don't know about it.
If you do implement your MySQL solution, please, please, please, keep
us informed about how it works for you. We would like to know more
and are always willing to look at new technologies but aren't too
accepting of hand waving.
> On 2/12/11 11:33 PM, Doug Barton wrote:
>> On 02/11/2011 01:51 PM, fddi wrote:
>>> I understand you, but the advantage of having mysql backend is that
>>> if one of the two servers dies, the other keeps running with up to
>>> date informations, and can also be updated wit new informations.
>>> the other server comes up again it will automatically sync itself
>>> using mysql replica mechanism. if I use file backend I have to
>>> manually sync it, and how to keep tracks of modifications ?
>>> for this I choose mysql backend
>> Two questions, how often do you anticipate one of the masters
>> failing, and how much data are you talking about? Generally the
>> number of times a server fails is going to be pretty small, if it's
>> not, you've got bigger problems.
>> If you're not talking about a huge amount of data here (and from
>> what you've described in previous posts, you're not) then you are
>> fairly dramatically over-architecting your solution here.
>> Personally I think David had a great idea in regards to using
>> nsupdate to update both masters at the same time. If you really
>> think that one of them is going to fail often enough to justify an
>> automated solution than scripting something that utilizes rsync
>> shouldn't be too hard.
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