multi-master with mysql backend
Gordon A. Lang
glang at goalex.com
Mon Feb 14 18:18:20 UTC 2011
FWIW, I feel compelled to chime in -- for those who haven't already begun
to filter out this thread.....
We have many thousands of records (internally) in hundreds of zones,
We have 8 DNS servers providing authoritative and recursive service to
thousands of internal clients.
All DNS servers are slaves to a single, semi-hidden master.
The master's "service addresses" is statically host routed to the servers
currently providing the master DNS service, with the service addresses
being assigned to loopback interface on the server.
If the active master dies, then I run a simple script on another working
DNS server to promote it to master, and I change a static host route in
the layer-3 switches to direct zone transfer and DDNS traffic to the new
server. I can restore the master DNS functionality on any other DNS
server within seconds.
The weakness of this system is that I don't trust an automatic failover,
so zone transfers and new DDNS requests have to wait until someone on my
team is notified of the problem, and they log in, and implement the flip.
We do have a mysql-based management system, but only for the non-dynamic
zones, and the zone files are pushed out to the active master using scp
and rndc. I would never install the database on an actual DNS server --
for many, many reasons.
Sorry if I come across as harsh, but the thought of installing a database
system on every DNS server that might need to become master seems
Ah. There, I feel much better now having said that.
Gordon A. Lang / 313-819-7978
----- Original Message -----
From: Mike Mitchell
Cc: bind-users at lists.isc.org
Sent: Monday, February 14, 2011 10:52 AM
Subject: RE: multi-master with mysql backend
I'd keep two copies of the BIND config, one that has all the zones as
"master", and one that has all the zones as "slave". When the master dies,
run a little script on a slave that freezes the zones, edits the SOA to make
that server the MNAME and increment the serial, then thaws the zone. Swap
out the config with the "master" config, and now you have a new master.
Before the broken master comes back online, swap out its config with the
No need for rsync or mysql, BIND replication does all the work for you.
Just be sure the updates go to the server listed in the MNAME field of the
From: bind-users-bounces+mike.mitchell=sas.com at lists.isc.org
[bind-users-bounces+mike.mitchell=sas.com at lists.isc.org] on behalf of Bill
Larson [wllarso.dns at gmail.com]
Sent: Monday, February 14, 2011 10:39 AM
Cc: bind-users at lists.isc.org
Subject: Re: multi-master with mysql backend
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 solution.
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 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
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. When
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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