[Linux-cluster] how to handle fence for a simple apache active/passive cluster with virtual ip on 2 virtual machine
Digimer
lists at alteeve.ca
Sat Feb 1 21:22:08 UTC 2014
No. When a node is lost, fenced is called. Fenced informs DLM that a
fence is pending and DLM stops issuing locks. Only after fenced confirms
successful fence is DLM told. The DLM will reap locks held by the
now-fenced node and recovery can begin.
Anything using DLM; rgmanager, clvmd, gfs2, will block. This is by
design. If you ever allowed a cluster to make an assumption about the
state of a lost node, you risk a split-brain. If a split-brain was
tolerable, you wouldn't need an HA cluster. :)
digimer
On 01/02/14 04:11 PM, nik600 wrote:
> Ok but is not possible to ignore fence?
>
> Il 01/feb/2014 22:09 "Digimer" <lists at alteeve.ca
> <mailto:lists at alteeve.ca>> ha scritto:
>
> Ooooh, I'm not sure what option you have then. I suppose
> fence_virtd/fence_xvm is your best option, but you're going to need
> to have the admin configure the fence_virtd side.
>
> On 01/02/14 03:50 PM, nik600 wrote:
>
> My problem is that i don't have root access at host level.
>
> Il 01/feb/2014 19:49 "Digimer" <lists at alteeve.ca
> <mailto:lists at alteeve.ca>
> <mailto:lists at alteeve.ca <mailto: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
> <https://access.redhat.com/__site/documentation/en-US/Red___Hat_Enterprise_Linux/6/html/__Cluster_Administration/index.__html>
>
> <https://access.redhat.com/__site/documentation/en-US/Red___Hat_Enterprise_Linux/6/html/__Cluster_Administration/index.__html
> <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?
>
> --
> Linux-cluster mailing list
> Linux-cluster at redhat.com <mailto:Linux-cluster at redhat.com>
> <mailto:Linux-cluster at redhat.__com
> <mailto:Linux-cluster at redhat.com>>
> https://www.redhat.com/____mailman/listinfo/linux-cluster
> <https://www.redhat.com/__mailman/listinfo/linux-cluster>
> <https://www.redhat.com/__mailman/listinfo/linux-cluster
> <https://www.redhat.com/mailman/listinfo/linux-cluster>__>
>
>
>
>
>
> --
> 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?
>
> --
> Linux-cluster mailing list
> Linux-cluster at redhat.com <mailto:Linux-cluster at redhat.com>
> https://www.redhat.com/__mailman/listinfo/linux-cluster
> <https://www.redhat.com/mailman/listinfo/linux-cluster>
>
>
>
--
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?
More information about the Linux-cluster
mailing list