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From "ASF subversion and git services (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CLOUDSTACK-3163) KVM Virtual Router startup time is painfully long
Date Thu, 25 Jul 2013 23:35:49 GMT

    [ https://issues.apache.org/jira/browse/CLOUDSTACK-3163?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13720239#comment-13720239
] 

ASF subversion and git services commented on CLOUDSTACK-3163:
-------------------------------------------------------------

Commit 17a675942cbd1f86a3441ec8299517f660656694 in branch refs/heads/master from [~yasker]
[ https://git-wip-us.apache.org/repos/asf?p=cloudstack.git;h=17a6759 ]

Bring back vm_data.sh which deleted by a KVM related commit

The following commit removed vm_data.sh, but the file shared by Xen as well.

Bring the file back.

commit 28855b4987c9274d15a539b9d7ae26c0073b0651
Author: Marcus Sorensen <marcus@betterservers.com>
Date:   Wed Jul 24 13:58:17 2013 -0600

    Summary: Get away from dozens of ssh/scp calls for KVM vm_data push

    Detail: userdata and vm metadata take a long time to program on KVM routers.
    This does it all in one go, processed on the router.

    BUG-ID: CLOUDSTACK-3163
    Tested-by: Wido
    Signed-off-by: Marcus Sorensen <marcus@betterservers.com> 1374695897 -0600

                
> KVM Virtual Router startup time is painfully long
> -------------------------------------------------
>
>                 Key: CLOUDSTACK-3163
>                 URL: https://issues.apache.org/jira/browse/CLOUDSTACK-3163
>             Project: CloudStack
>          Issue Type: Bug
>      Security Level: Public(Anyone can view this level - this is the default.) 
>          Components: KVM
>    Affects Versions: pre-4.0.0
>         Environment: CloudPlatform 3.0.3, but I don't see any changes to the relevant
code (I think) on master
>            Reporter: Andrew Bayer
>            Assignee: Marcus Sorensen
>            Priority: Critical
>             Fix For: 4.2.0
>
>
> When you've got a couple thousand instances, spread across 10 or so pods, virtual router
startup time is near crippling - actually, if you don't enable the option to have virtual
routers only populated with instances in their pod, it *is* crippling, in that the virtual
routers don't finish starting before the management server decides they've timed out and tries
to start a new one.
> This seems to be the result of a few painful inefficiencies:
> - The same codepath is followed whether you're adding a new instance to an already running
VR, or adding two hundred already running instances to a new VR. So each ssh/scp/sed/cp/chmod/etc
command is replicated for each instance, rather than finding efficiencies by doing things
across the whole set of instances. 
> - But what really eats up the time is the population of vm data - for each piece of vm
data (which, from a rough look at the code, seems to be something like 10 or 11 data files),
there are something like 7 ssh calls and an scp call. So that means that per instance, we
have somewhere around 80 to 90 ssh/scp calls, plus the single ssh call for dhcp_entry.sh.
So with 200 instances, that's 1600 to 1800 ssh/scp calls on a single VR, with all the overhead
entailed in opening that many ssh connections, starting bash, etc, etc... Given that in my
experience, a VR with ~200 instances takes ~90 minutes to start up (I may be misremembering
slightly - it could be ~200 instances takes closer to 60 minutes, and ~300 takes closer to
90), that works out to 3 seconds or so per ssh/scp, which doesn't seem implausible to me.

> So, this shouldn't be this way. At a minimum, there's no reason not to offload the whole
process from a script run on the host making repeated ssh calls to the VR to a script on the
VR that gets called from the host, albeit possibly a temporary one that's generated on the
fly and copied over to the VR. That alone would probably save most of the VR startup time,
just by dropping the number of ssh/scp connections per instance from 80-90 to 3 (dhcp_entry.sh
call, scp of temporary script, execution of temporary script).

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