Db2

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  • 1.  Db2 HADR and Pacemaker, VIP vs No-VIP

    Posted Fri April 19, 2024 11:31 AM
    Edited by Jim Pearon Fri April 19, 2024 11:46 AM

    I have utilized HADR since it was first added to DB2, and TSAMP for HA automation since 2013.  I am currently testing out Pacemaker for HA automation.  Historically, I have implemented with, and without, Primary VIPs depending on the year and the environment.  My usual considerations are Configuration Management, Split Brain risk, failover time, supportability, Network Team considerations, and anything else I may be forgetting.  This specific implementation spans subnets, so there are VLAN considerations.  I have found a few pertinent discussions here and have reviewed those.

    Given such an implementation, does anyone have experiences, recommendations, thoughts, etc. they are willing to share on the topic of to VIP or not to VIP?

    Thanks in advance, if you do!

    #Db2



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    Jim Pearon
    Contractor
    Winsupply
    Moraine OH
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  • 2.  RE: Db2 HADR and Pacemaker, VIP vs No-VIP

    Posted 29 days ago

    The primary reason I have a used VIP is to have application able to connect to the new primary database in case of a database failover (or failback)

    Since you mention the implementation spans subnets you need to implement an Overlay IP instead. This is documented in below link for AWS implementation.

    https://www.ibm.com/support/pages/setting-two-node-db2-pacemaker-cluster-overlay-ip-virtual-ip-aws-db2-v11580

    We have used Pacemker Overlay IP and has worked flawlessly in our tests. I appreciate in some applications you can provide two IP addresses however it was not the case for our app and I have not tested it.

    We have however tested the use of ACR  (Automatic Client reroute) for our setup and found Pacemker Overlay IP provides much faster failover time and worked every time. In comparison ACR was a hit or a miss.



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    Divaker Goel
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  • 3.  RE: Db2 HADR and Pacemaker, VIP vs No-VIP

    Posted 29 days ago

    Thank you for this, @Divaker Goel !

    I will share that on a FileNet P8 Platform implementation with multiple databases on a server, I observed better time-to-live for the application (JDBC Type 4 connections) using ACR.  However I attributed this to the application needing to connect to multiple databases in order to begin processing, and the VIPs depending on all other resources to come online, led to the quicker time-to-live for the application.  Of course this testing was completed long ago in Db2 v10.1 with TSAMP handling the automation, and currently with Pacemaker having quicker time-to-live than TSA it would interesting to retest that application in v11.5 with Pacemaker.

    Thanks again!



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    Jim Pearon
    Contractor
    Winsupply
    Moraine OH
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  • 4.  RE: Db2 HADR and Pacemaker, VIP vs No-VIP

    IBM Champion
    Posted 28 days ago

    Hi Jim,

    I have tested various Pacemaker configurations a while ago, with and without VIP (and ACR), albeit in an AWS VPC (where the failover across subnets, i.e. Availability Zones, is enabled via the AWS Overlay IP addresses).

    What I found was, unsurprisingly, that when both VIP (Overlay IP) and ACR are used, the application switching is as seamless as it can get following a DB failover.

    I wrote two ebooks on the subject, which you can download (for free :-) from here:

        Automating HADR failovers with Pacemaker

        Configuring Db2 Pacemaker HADR cluster with QDevice in AWS

    Hope this helps in your research, even if it's not strictly what you asked for!

    Some time later, after I've done all of the above (research, testing, ebooks), I have stumbled upon the following articles which describe how an even more seamless application switchover can be configured:

        Operation of automatic client reroute for connections to Db2 on Linux, UNIX, and Windows systems from Java clients

        Operation of automatic client reroute for connections to the Db2 server from an application other than a Java application

     I haven't had the time (yet) to test the "seamless failover", as described in the articles above, but am planning to, and if this really works as described then the applications will truly never be aware of any failovers taking place on the DB level!

    Regards, Damir



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    Damir Wilder
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  • 5.  RE: Db2 HADR and Pacemaker, VIP vs No-VIP

    Posted 27 days ago

    Thank you so much for sharing this, @Damir Wilder !

    I will definitely review all of this.

    The FileNet P8 Platform applications utilized seamless failover.  I was not able to participate in most of the 'fun' testing.  However I did make a new friend when those user queries, which were not following the logical model, attempted things like exhausting our temp space - the WLM_CANCEL_ACTIVITY stored procedure.  Seamless failover handled any 'force application' SQL30081N/-4498 quite well, and immediately reissued the problematic query without any notification to the application.  The FileNet applications did respond well to the WCA SP's SQL4725N.

    Thanks again,

    Jim



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    Jim Pearon
    Contractor
    Winsupply
    Moraine OH
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