Difference between revisions of "Ajcody-Clustering"

m (Other Clustering RFE's And Bugs)
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*"HA/DR through Log Shipping"
 
*"HA/DR through Log Shipping"
 
** http://bugzilla.zimbra.com/show_bug.cgi?id=42231
 
** http://bugzilla.zimbra.com/show_bug.cgi?id=42231
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===Vmware Virtualization and Clustering===
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* "No support for RHEL Clustering on top of VMware"
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** http://bugzilla.zimbra.com/show_bug.cgi?id=53728
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At this time, we have no official declared position about supporting vSphere [vmware] for clustering.
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See also:
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* [[Performance_Recommendations_for_Virtualizing_Zimbra_with_VMware_vSphere_4#vSphere_Cluster_Recommendations]]
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* "Zimbra on NFS Storage through VMware ESX"
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** http://bugzilla.zimbra.com/show_bug.cgi?id=50635
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** Will most likely result in a change in our NFS policy as well as statement of support for vSphere clustering.
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*** Current NFS policy
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**** http://bugzilla.zimbra.com/show_bug.cgi?id=33221#c8
  
 
===RFE's/Bug Related To Supporting Clustering Options===
 
===RFE's/Bug Related To Supporting Clustering Options===

Revision as of 21:53, 26 November 2010

Attention.png - This article is NOT official Zimbra documentation. It is a user contribution and may include unsupported customizations, references, suggestions, or information.

Clustering Topics

Actual Clustering Topics Homepage


Please see Ajcody-Clustering

My Other Clustering Pages


RFE I made based upon the experience above:

Critical Bugs/RFE's - False Restarts And So Forth

Log Rotation Causes Cluster Failover

See:

Recommendations to work around bug until fix is released - 2 methods:

  • First Method - disable log rotation
    • Remove the zmmtaconfigctl restart from the /etc/logrotate.d/zimbra file so that it will not attempt to restart the service that is being detected as down. We can remove the line that reads:
su - zimbra -c "/opt/zimbra/bin/zmmtaconfigctl restart"
    • That will stop these failures, but will affect the logging for zmmtaconfigctl, probably causing it to write to a nonexistent file. We haven't seen problems in zmmtaconfig for a long time, so this is a pretty low risk workaround.
  • Second Method - disable software monitoring in general

Software Monitoring Causes Problems

  • To Disable software monitoring.
    • This will prevent failover if zmcluctl finds a service down. It will not prevent failover if there is a hardware fault detected by the cluster software.
    • To disable it, check /opt/zimbra-cluster/bin/zmcluctl and find the 'status' section. It's the last of the three (start, stop, status). You will need to find the lines that read 'exit($rc);' and change them to read 'exit(0);'.
    • To also increase the chance of getting more information in the log on what might be going on:
      • In /opt/zimbra-cluster/bin/zmcluctl you should see a line like:
        • my @output = `su - zimbra -c 'zmcontrol status'`;
      • Change that to:
        • my @output = `su - zimbra -c 'date >> /opt/zimbra/log/zmcluster-status.log ; zmcontrol status >> /opt/zimbra/log/zmcluster-status.log 2>> /opt/zimbra/log/zmcluster-status.log'`;
      • That should give us more logging. I believe zmcluctl is read every time from disk when it does the check, so no restart of services should be needed.

RHEL 5 Clusters And Cisco Switches

Please see the following:

Mysql Related Items Impacting Cluster

Please see:

Other Misc Bug/RFEs

Other bugs/rfe's you might be interested in looking at:

Failover Occurring Prior To Mysql Shutting Down - RHCS

Here is the summary of the situation that was sent for a case on the matter.

Regarding RHCS desired configuration -
In particular, it looks like mysqld can at times take quite a long time to shutdown, especially in situations when write IO is limited on the mysql db partition, and mysqld must write cache data to disk safely before shutting down. We believe this should be reflected in the "rc=1" output from "zmcontrol stop" - if mysqld does not stop within the 60 seconds via /opt/zimbra/bin/zmcontrol (via /opt/zimbra/bin/mysql.server), and then what appears to be happening is that RHCS either tries to unmount the filesystem and/or just kill -KILL the running process, which in turns causes mysqld to die ungracefully and cause the mysqld startup on the other box to go through a long log replay. The net result is one of two scenarios:
(a) mysqld takes longer to startup than it would have taken to shutdown (normal shutdown can take 0-10 minutes if mysqld has to flush a bunch of data to write out)
(b) mysqld is still running when RHCS tries to unmount the filesystem, which then fails, and therefore the failover fails
What we'd like to be able to recommend is a more robust failover logic, such as:
1. Run zmcontrol stop, check output
2. If failed, wait X seconds (e.g., 120 seconds)
3. Run zmcontrol stop again
4. If failed, wait X seconds
5. Run zmcontrol third time
6. If failed third time, try a kill -KILL and force unmount
If RHCS can be configured to do this, it would be the best way to handle this situation. The problem with modifying zmcontrol to have this logic internally is that it should not be granted the decision to wait indefinitely, in the case that mysqld is having a critical problem and is not shutting down. Having an external process manage this logic allows for additional triangulation on the determination of the situation, and allows additional capabilities such as monitoring the files in /opt/zimbra/db/data to confirm that files are changing. For example, if mysqld is still running and no files have changed in /opt/zimbra/db/data for a significant amount of time, it may indicate that mysqld is locked up, and other steps may be required. zmcontrol would not be able to handle all of this logic internally due to the needs for additional external monitoring outside of the zmcontrol process, including return code from the script.

RFE that was made about Zimbra adjusting the our script and the wait time:

Good Summary For RHEL Clustering


This is a good solid summary about RHEL clustering:

http://www.linuxjournal.com/article/9759

Active-Active Clustering


There is a bug(rfe) for active-active configuration. Please see:

http://bugzilla.zimbra.com/show_bug.cgi?id=19700

Non-San Based Fail Over HA/Cluster Type Configuration


This RFE covers issues when your wanting a "copy" of the data to reside on an independent server - LAN/WAN.

Please see:

Vmware Virtualization and Clustering

At this time, we have no official declared position about supporting vSphere [vmware] for clustering.

See also:

RFE's/Bug Related To Supporting Clustering Options


Other Clustering RFE's And Bugs


HA-Linux (Heartbeat)



HA-Linux How-To For Testing And Educational Use

References:


Actual HA-Linux How-To For Testing And Educational Use Homepage

Please see Ajcody-Notes-HA-Linux-How-To

Motive Behind How-To

I hope this gives an easy way to setup through some clustering concepts for an administrator to gain some real-world experience when they currently have none. I plan on walking through each "function" that is behind clustering rather than jumping to an end setup (Linux-HA, Shared Storage, And Zimbra).

The structure will be:

  • Setup two machines (physical or virtual)
    • Emphasis physical hostname / ip vs. the hostname and ip address that will be for HA.
  • Setup virtual hostname and ip address for HA.
    • Explain and do ip failover between the two machines.
  • Setup a disk mount, we'll use probably use a nfs export from a third machine.
    • This will give us an example of expanding the HA conf files to move beyond the ip address failover.
    • Adjust HA conf's to now export via nfs a local directory from each server. This will not be a shared physical disk of course.
  • Setup a shared disk between the two servers and include it in the HA conf files.
    • Can use drbd or maybe figure out a way to share a virtual disk between the two vm's.
  • Setup a very simple application to include between the two machines. Something like apache or cups.
  • Go back and now readjust all variables between monitoring type (automatic) failover and simple manually initiated.

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