On Sat, 16 Sep 2006, Manuel Vázquez Acosta wrote:
I've done it recently.
I don't have access to my notes or any of the config files at the moment but
can probably send you more details during the week.
It involves:
-Setting up slony as per normal with a master and a slave
-Setting up heartbeat to use a virtual IP on the master that your
applications will use when they want to connect to the database.
-Writing a script in heatbeat's resource.d that gets called on heart beat
start events for slony.
The script I wrote supported start and status operations.
For the start operation it had two modes
1) A controlled switch over mode that I activated with a touch file in /tmp.
This mode did a MOVE SET, and was for promoting the slave when the master
was still running (ie in preparation for taking the master down for
maintenance).
2) A fail over mode that would execute if heartbeat on the slave detected that
the master went away.
The script also had a status command that would return if the database on
the local host was the origin for the slony replication set.
You also want to make sure that the auto_failback (It might be named
something different) is turned off so IF the primary does come back online
heartbeat does not try to make it the master again.
We took the approach that if the system did a fail over then the master was
dropped from the replication set and if it did come back online it would not
get automatically added back as a slony slave. The system would run
without a second database until someone manually re-provisioned the primary
server as a new slony slave.
As Andrew indicated, if your primary server goes down and the secondary
becomes the master then any data on the primary that hadn't yet made it to
the secondary server at time of failover might be lost. You would still be
able to access the database on the primary server (Once you fix whatever
went wrong in the first place) but slony won't be able to send the
unreplicated data out.
I don't have any experiences with failures in a production enviornment to
say how well it works.
Steve
Hi all,
I'm trying to set up a Active/Pasive configuration for PostgreSQL
using Slony and Heartbeat.
I'm wondering if anyone has done it before, and give some ideas.
Best regards
Manuel.
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