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https://issues.apache.org/jira/browse/CLOUDSTACK-10310?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16641913#comment-16641913
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ASF GitHub Bot commented on CLOUDSTACK-10310:
---------------------------------------------

csquire commented on issue #2722: CLOUDSTACK-10310 Fix KVM reboot on storage 
issue
URL: https://github.com/apache/cloudstack/pull/2722#issuecomment-427859929
 
 
   This PR doesn't seem to completely fix the reboot problem. We installed the 
RC release with this PR on a test system and are still able to get the KVM host 
to reboot by using iptables to drop outgoing requests to NFS. My investigation 
shows that the line [`storage = 
conn.storagePoolLookupByUUIDString(uuid);`](https://github.com/apache/cloudstack/blob/4.11/plugins/hypervisors/kvm/src/com/cloud/hypervisor/kvm/resource/KVMHAMonitor.java#L95)
 blocks indefinitely.  So, `kvmheartbeat.sh` is never executed, a host 
investigation is started, the host with blocked NFS is marked as `Down` and 
finally all VMs on that host are rescheduled and result in duplicate VMs.
   
   I pulled a thread dump and found the KVMHAMonitor thread will hang here 
until NFS is unblocked, didn't dig any deeper yet though.
   
   ```"Thread-20" - Thread t@135
      java.lang.Thread.State: RUNNABLE
           at com.sun.jna.Native.invokePointer(Native Method)
           at com.sun.jna.Function.invokePointer(Function.java:470)
           at com.sun.jna.Function.invoke(Function.java:404)
           at com.sun.jna.Function.invoke(Function.java:315)
           at com.sun.jna.Library$Handler.invoke(Library.java:212)
           at com.sun.proxy.$Proxy3.virStoragePoolLookupByUUIDString(Unknown 
Source)
           at org.libvirt.Connect.storagePoolLookupByUUIDString(Unknown Source)
           at 
com.cloud.hypervisor.kvm.resource.KVMHAMonitor$Monitor.runInContext(KVMHAMonitor.java:95)
           - locked <1afb3370> (a java.util.concurrent.ConcurrentHashMap)
           at 
org.apache.cloudstack.managed.context.ManagedContextRunnable$1.run(ManagedContextRunnable.java:49)
           at 
org.apache.cloudstack.managed.context.impl.DefaultManagedContext$1.call(DefaultManagedContext.java:56)
           at 
org.apache.cloudstack.managed.context.impl.DefaultManagedContext.callWithContext(DefaultManagedContext.java:103)
           at 
org.apache.cloudstack.managed.context.impl.DefaultManagedContext.runWithContext(DefaultManagedContext.java:53)
           at 
org.apache.cloudstack.managed.context.ManagedContextRunnable.run(ManagedContextRunnable.java:46)
           at java.lang.Thread.run(Thread.java:748)
   
      Locked ownable synchronizers:
           - None```

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> KVM hosts reboot if there is a short transient storage error
> ------------------------------------------------------------
>
>                 Key: CLOUDSTACK-10310
>                 URL: https://issues.apache.org/jira/browse/CLOUDSTACK-10310
>             Project: CloudStack
>          Issue Type: Improvement
>      Security Level: Public(Anyone can view this level - this is the 
> default.) 
>          Components: KVM
>    Affects Versions: 4.9.0, 4.10.0.0
>            Reporter: Sean Lair
>            Priority: Major
>
> If the KVM heartbeat file can't be written to, the host is rebooted, and thus 
> taking down all VMs running on it.  The code does try 5x times before the 
> reboot, but the there is not a delay between the retires, so they are 5 
> simultaneous retries, which doesn't help.  Standard SAN storage HA operations 
> or quick network blip could cause this reboot to occur.
> Some discussions on the dev mailing list revealed that some people are just 
> commenting out the reboot line in their version of the CloudStack source.
> A better option (and a new PR is being issued) would be have it sleep between 
> tries so it isn't 5x almost simultaneous tries.  Plus, instead of rebooting, 
> the cloudstack-agent could just be stopped on the host instead.  This will 
> cause alerts to be issued and if the host is disconnected long-enough, 
> depending on the HA code in use, VM HA could handle the host failure.
> The built-in reboot of the host seemed drastic



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