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From Rohit Yadav <>
Subject Re: [DISCUSS] Host HA in 4.11
Date Tue, 29 Aug 2017 06:23:14 GMT

Over last couple of weeks, we've improved the host-ha implementation drastically with following

- Reduced number of background polling tasks from 4 to 1

- Added additional tests around degrading, fencing, and recovering FSM states with real KVM
hypervisor, these tests run/work with Trillian

- Refactored the implementation to be state/event driven than poll/loop driven

- Fixed VM HA for recovered host

The host-ha PR is ready for merging now, it has passed tests on Travis, Trillian and BVT:

I'll keep the PR open for sometime this week to seek any last minute feedback and/or comment
and merge by eod tomorrow, thanks.

- Rohit

From: Rohit Yadav <>
Sent: Thursday, July 13, 2017 12:18:58 PM
Cc: Nathan Johnson; David Mabry; Aaron Hurt
Subject: Re: [DISCUSS] Host HA in 4.11

Thanks for the interest Simon, the feature has two HA provider (plugins, one for simulator
and another for KVM+NFS) that can be used as reference implementations.

- Rohit

From: Simon Weller <>
Sent: 12 July 2017 20:59:38
Cc: Nathan Johnson; David Mabry; Aaron Hurt
Subject: Re: [DISCUSS] Host HA in 4.11

We are very excited about this feature set, as it adds some really important features for

We don't use NFS, so I think our goal will be seeing what we can contribute to include Ceph
on the supported storage list.

- Si
From: Rohit Yadav <>
Sent: Wednesday, July 12, 2017 5:43 AM
Subject: [DISCUSS] Host HA in 4.11


Few months ago I had started discussion on Host HA for CloudStack and given 4.10 is voted
and to be announced with master branch cut I would like to re-kick discussion around reviewing
and acceptance of the feature that is pending since Feb 2017.

To briefly share some key points:

- This feature is disabled by default and provides zone/cluster/host level kill switches

- This brings in a reliable way to fence (power off) and recover (reboot) a host

- Allows implementation of HA provider plugin specific to a hypervisor and storage stack,
by default we've implemented a plugin for hosts that have KVM+NFS

- For more details please read the FS:
Host HA - Apache Cloudstack - Apache Software Foundation<>
CLOUDSTACK-9782. Branch. Yet to start, share the PR. Introduction. CloudStack lacks a way
to reliably fence a host, the idea of the host-ha feature is to provide a ...

I had also given a talk about this feature during CCCNA17:

Reliable host fencing -

Pull request: (as soon as the 4.10->4.11
db upgrade paths are fixed, I can rebase and fix the branch)

[4.11/Future] CLOUDSTACK-9782: Host HA and KVM HA provider by rhtyd · Pull Request #1960
· apache/cloudstack<>
Host-HA offers investigation, fencing and recovery mechanisms for host that for any reason
are malfunctioning. It uses Activity and Health checks to determine current host state based
on which it m...

- Rohit<>

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