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Re: unixODBC failover

Cname handling is application-specific; your app gets all of the names and can either always use the first one, or rotate through them (or pick a random one). The DNS server can either always return them in the same order or rotate in various ways. Bind4 needed that rotation configured explicitly, while 8 had an option to not rotate, and 9 can be compiled to have the option to not rotate (the option is rrset-order). Just to put this on your specific environment even more. :)  It's how I distribute CFEngine load...

Either way, http://dev.mysql.com/downloads/mysql-proxy may be available as a package on your distro. It's on Ubuntu.


Herbie <technowombat@yahoo.com> wrote:
Well, I'm waiting to hear back from the apps maker exactly what it does 
when the server is unavailable. I know that the app itself does not handle
a failover server.

The multiple CNAME entry, or DNS round-robin, is only going to be useful
as a cheap load sharing device, rather than a failover, what I mean is,
that dependent on how your server caches hostnames, it will either show
Server A or Server B when queried, so the load will be applied between
both servers.

What I'm looking for is a more logical

Unless Server A is down, use Server A
else use Server B

where Server A should handle the load under normal circumstance, with
Server B only being used if Server A is unavailable.

This is the method used in pam_ldap and nss_ldap, and some other LDAP
based apps, I guess I was just surprised it wasn't that simple under
mySQL. So does anyone know some mySQL proxy software that will do this
assuming the manufacturer tells me their app tries the server more than


On Thu, 19 Dec 2013, Danny Sauer wrote:

If it automatically retries at the app level then it could be as easy as a cname with multiple entries. If not, then I think you're sick using some kind of proxy in between; nothing I'm aware of at the mysql protocol level does the retry thing for you. Ideally the backend for the odbc layer can? :)

Herbie <technowombat@yahoo.com> wrote:
I'm playing with an app that uses the unixODBC layer to communicate
with a
mySQL database. I'm trying to figure if there's an easy way I can make
fail over to a backup database if the first one is unavailable. In an
ldap.conf it's as easy as adding an extra server on the host line.


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