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From Marcus Sorensen <shadow...@gmail.com>
Subject Re: [DISCUSS] KVM HA
Date Wed, 07 Aug 2013 20:46:28 GMT
I'm not sure we can rely on IPMI to tell us much about the host status
itself. It's easy to use it for checking on basic poweron/poweroff,
temperature, etc, but not so easy to tell if something is wrong with
the OS, config, or at the software level.

However, I did mention support in that thread early on for sending an
IPMI poweroff for hosts that cloudstack has determined are down and
starts migrating vms for, as a safety precaution.

On Wed, Aug 7, 2013 at 2:41 PM, Marcus Sorensen <shadowsor@gmail.com> wrote:
> Does KVMInvestigator work on all shared primary storage, or just NFS?
> I'm only familiar with the NFS KVMHA directories.
>
> From this it seems like a clean stop of the KVM agent still shouldn't
> trigger any issues/HA, correct?
>
> On Wed, Aug 7, 2013 at 2:28 PM, Edison Su <Edison.su@citrix.com> wrote:
>> There is long time issue related to KVM HA, see bug: CLOUDSTACK-3535. Basically,
HA won't be triggered, if KVM agent is stopped either normally nor abnormally, HA only be
triggered if the network between mgt server and kvm host is disconnected and the network between
KVM hosts in the same cluster is disconnected.
>> Here is how the KVM HA works after the fix for CLOUDSTACK-3535:
>> 1. If agent is stopped, agent will send a shutdown request to mgt server, mgt server
will mark the host as disconnected, while still maintain the host in pingmap. Code is in AgentManagerImpl->AgentHandler-
    >ProcessRequest-> disconnectWithoutInvestigation
>> 2. After ping.interval, mgt server will find the host is ping timeout, then start
HA investigation for the host. Code is in AgentMonitor->run-> disconnectWithInvestigation
>> 3. Mgt server will call all the available Investigators to investigate the status
of host.
>>      The current investigators will be called for KVM host:
>>         UserVmDomRInvestigator->isAgentAlive, will send PingTestCommand to the
host's neighbor. PingTestCommand will ping host's private ip address, if ping is reachable,
means host is up, otherwise, host's state is unknown. So this investigator can only detect
host is in up state.
>>                 KVMInvestigator, which is newly added, will send a CheckOnHostCommand
to host's neighbor. CheckOnHostCommand will check the heartbeat of host(heartbeat is stored
on shared primary storage). Ideally, it will detect host is down or up.
>>
>>      Combined with   UserVmDomRInvestigator  and KVMInvestigator, mgt server should
find out the status of host. But there is case, these two investigators can report wrong status
of host:
>>           Host is in a network partition, while the KVM agent is down(thus heartbeat
is stopped)
>> 4. After investigator reports status of host, if host is down, then start HA for
VMs created on the host.
>>
>>
>> Improvement:
>>      Per suggestion from Lennert den Teuling,  we'd better use IPMI to detect host
status, which is more reliable than ping and heartbeat, as IPMI has its own network, less
likely has network partition.
>>
>>

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