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From Koushik Das <>
Subject Re: [DISCUSS][FS] Host HA for CloudStack
Date Mon, 20 Feb 2017 06:15:59 GMT

Thanks for the effort you have put in writing the FS. I have some questions based on my initial
reading of the FS.

1. “Host HA” – In the FS you are talking about a generic HA framework but it is not
clear what is meaning of “host HA”. Is it something like all or some VMs running on a
host will be started on another host(s) in case of a failure or is it something else? How
is it different from the existing “VM HA” that is already there?
2. You have mentioned that “Cloudstack lacks a way to reliably fence host”. Cloudstack
considers VM as a 1st class object and so provides fencing for VM instead of host. There are
hypervisor specific plugins that implement mechanism to fence a VM. I am not sure if it makes
sense to expose host fencing as end user doesn’t care about it. Now the VM fencing implementation
can use something like “host fencing” internally.
3. There is an existing HA framework which provides plugins for doing investigation if a VM
is alive or not, host is alive or not, fencing of VM in case it is not alive. It will be good
to understand the limitations of the existing framework and how the new framework helps in
solving these problems. We also need to understand if the limitation is in the framework or
some specific plugin implementation that is causing issues. Reference to JIRA issues would
4. You have mentioned about ipmi to investigate host failure. I would like to understand why
same can’t be used in the existing framework.


On 16/02/17, 4:48 PM, "Rohit Yadav" <> wrote:

    I would like to start discussion on a new feature - Host HA for CloudStack.
    CloudStack lacks a way to reliably fence a host, the idea of the host-ha feature is to
provide a general purpose HA framework and HA provider implementation specific for hypervisor
that can use additional mechanism such as OOBM (ipmi based power management) to reliably investigate,
recover and fence a host. This feature can handle scenarios associated with server crash issues
and reliable fencing of hosts and HA of VM. The first version will have HA provider implementation
for KVM (and for simulator to test the framework implementation, and write marvin tests that
can validate the feature on Travis and others).
    Please have a look at the FS here:
    Looking forward to your comments and questions.
    53 Chandos Place, Covent Garden, London  WC2N 4HSUK

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