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From "Koushik Das" <>
Subject Re: Review Request: CLOUDSTACK-606: Starting VM fails with 'ConcurrentOperationException' in a clustered MS scenario
Date Fri, 01 Feb 2013 09:25:35 GMT

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(Updated Feb. 1, 2013, 9:25 a.m.)

Review request for cloudstack, Abhinandan Prateek and Alex Huang.


Updated exception message as the fix is not merged yet.


The issue happens randomly when hosts in a cluster gets distributed across multiple MS. Host
can get split in following scenarios:
    a. Add host – MS on which add host is executed takes ownership of the host. So if 2
hosts belonging to same cluster are added from 2 different MS then cluster gets split
    b. scanDirectAgentToLoad – This runs every 90 secs. and check if there are any hosts
that needs to be reconnected. The current logic of host scan can also lead to a split
    The idea is to fix (b) to ensure that hosts in a cluster are managed by same MS. For (a)
only the entry in the database is going to be created except in case if the host getting added
is first in the cluster (in this case agent creation happens at the same time) and then (b)
will take care of connection and agent creation part. Since currently addHost only creates
an entry in the db there is a small window where the host state will be shown as 'Alert' till
the time (b) is scheduled and picks up the host to make a connection. The MS doing add host
will immediately schedule a scan task and also send notification to peers to start the scan

This addresses bug CLOUDSTACK-606.

Diffs (updated)

  api/src/com/cloud/agent/api/ PRE-CREATION 
  server/src/com/cloud/agent/manager/ ca0bf5c 
  server/src/com/cloud/cluster/ e341b88 
  server/src/com/cloud/host/dao/ 0881675 
  server/src/com/cloud/resource/ f82424a 



Manually tested the following scenarios:

- Added hostA in cluster1 from MS1, gets owned by MS1 as first host in cluster. Added hostB
in same cluster1 from MS2. Once both hosts are in 'Up' state ensure that they are owned by
the same MS (i.e. MS1).
- Error scenarios when host goes to disconnected, alert or down state (disconnected host from
network) and is reconnected back (connected to network). Ensure that once connected back,
host should be owned by same MS as other hosts in the cluster.
- Have a scenario where hosts are already in a distributed state (before the fix added hosts
to the same cluster from different MSs) and ensure that after applying the patch and retarting
the MSs distribution happens properly.
- Did basic validation in a single MS setup, added multiple hosts in a cluster and created
VMs on them.


Koushik Das

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