[Linux-cluster] how to handle fence for a simple apache active/passive cluster with virtual ip on 2 virtual machine

[nik600]

My problem is that i don't have root access at host level.
Il 01/feb/2014 19:49 "Digimer" <lists at alteeve.ca> ha scritto:

> On 01/02/14 01:35 PM, nik600 wrote:
>
>> Dear all
>>
>> i need some clarification about clustering with rhel 6.4
>>
>> i have a cluster with 2 node in active/passive configuration, i simply
>> want to have a virtual ip and migrate it between 2 nodes.
>>
>> i've noticed that if i reboot or manually shut down a node the failover
>> works correctly, but if i power-off one node the cluster doesn't
>> failover on the other node.
>>
>> Another stange situation is that if power off all the nodes and then
>> switch on only one the cluster doesn't start on the active node.
>>
>> I've read manual and documentation at
>>
>> https://access.redhat.com/site/documentation/en-US/Red_
>> Hat_Enterprise_Linux/6/html/Cluster_Administration/index.html
>>
>> and i've understand that the problem is related to fencing, but the
>> problem is that my 2 nodes are on 2 virtual machine , i can't control
>> hardware and can't issue any custom command on the host-side.
>>
>> I've tried to use fence_xvm but i'm not sure about it because if my VM
>> has powered-off, how can it reply to fence_vxm messags?
>>
>> Here my logs when i power off the VM:
>>
>> ==> /var/log/cluster/fenced.log <==
>> Feb 01 18:50:22 fenced fencing node mynode02
>> Feb 01 18:50:53 fenced fence mynode02 dev 0.0 agent fence_xvm result:
>> error from agent
>> Feb 01 18:50:53 fenced fence mynode02 failed
>>
>> I've tried to force the manual fence with:
>>
>> fence_ack_manual mynode02
>>
>> and in this case the failover works properly.
>>
>> The point is: as i'm not using any shared filesystem but i'm only
>> sharing apache with a virtual ip, i won't have any split-brain scenario
>> so i don't need fencing, or not?
>>
>> So, is there the possibility to have a simple "dummy" fencing?
>>
>> here is my config.xml:
>>
>> <?xml version="1.0"?>
>> <cluster config_version="20" name="hacluster">
>>          <fence_daemon clean_start="0" post_fail_delay="0"
>> post_join_delay="0"/>
>>          <cman expected_votes="1" two_node="1"/>
>>          <clusternodes>
>>                  <clusternode name="mynode01" nodeid="1" votes="1">
>>                          <fence>
>>                                  <method name="mynode01">
>>                                          <device domain="mynode01"
>> name="mynode01"/>
>>                                  </method>
>>                          </fence>
>>                  </clusternode>
>>                  <clusternode name="mynode02" nodeid="2" votes="1">
>>                          <fence>
>>                                  <method name="mynode02">
>>                                          <device domain="mynode02"
>> name="mynode02"/>
>>                                  </method>
>>                          </fence>
>>                  </clusternode>
>>          </clusternodes>
>>          <fencedevices>
>>                  <fencedevice agent="fence_xvm" name="mynode01"/>
>>                  <fencedevice agent="fence_xvm" name="mynode02"/>
>>          </fencedevices>
>>          <rm log_level="7">
>>                  <failoverdomains>
>>                          <failoverdomain name="MYSERVICE" nofailback="0"
>> ordered="0" restricted="0">
>>                                  <failoverdomainnode name="mynode01"
>> priority="1"/>
>>                                  <failoverdomainnode name="mynode02"
>> priority="2"/>
>>                          </failoverdomain>
>>                  </failoverdomains>
>>                  <resources/>
>>                  <service autostart="1" exclusive="0" name="MYSERVICE"
>> recovery="relocate">
>>                          <ip address="192.168.1.239" monitor_link="on"
>> sleeptime="2"/>
>> <apache config_file="conf/httpd.conf" name="apache"
>> server_root="/etc/httpd" shutdown_wait="0"/>
>>                  </service>
>>          </rm>
>> </cluster>
>>
>> Thanks to all in advance.
>>
>
> The fence_virtd/fence_xvm agent works by using multicast to talk to the VM
> host. So the "off" confirmation comes from the hypervisor, not the target.
>
> Depending on your setup, you might find better luck with fence_virsh (I
> have to use this as there is a known multicast issue with Fedora hosts).
> Can you try, as a test if nothing else, if 'fence_virsh' will work for you?
>
> fence_virsh -a <host ip> -l root -p <host root pw> -n <virsh name for
> target vm> -o status
>
> If this works, it should be trivial to add to cluster.conf. If that works,
> then you have a working fence method. However, I would recommend switching
> back to fence_xvm if you can. The fence_virsh agent is dependent on
> libvirtd running, which some consider a risk.
>
> hth
>
> --
> Digimer
> Papers and Projects: https://alteeve.ca/w/
> What if the cure for cancer is trapped in the mind of a person without
> access to education?
>
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