[Libguestfs] Thoughts on nbdkit automatic reconnection

[Eric Blake]

On 9/19/19 4:50 AM, Richard W.M. Jones wrote:
> On Wed, Sep 18, 2019 at 01:59:01PM +0100, Richard W.M. Jones wrote:
>> We have a running problem with the nbdkit VDDK plugin where the VDDK
>> side apparently disconnects or the network connection is interrupted.
>> During a virt-v2v conversion this causes the entire operation to fail,
>> and since v2v conversions take many hours that's not a happy outcome.
>>
>> (Aside: I should say that we see many cases where it's claimed that
>> the connection was dropped, but often when we examine them in detail
>> the cause is something else.  But it seems like this disconnection
>> thing does happen sometimes.)
> 
> It turns out in the customer case that led us to talk about this, a
> Checkpoint firewall was forcing the VDDK control connection to be
> closed after an idle period.

Would TCP keepalive help here?

>  (The VDDK connection as a whole was not
> actually idle because data was being copied over the separate data
> port, but the firewall did not associate the two ports).  I believe
> nbdkit-retry-filter would have helped in this case because reopening
> the VDDK connection will reestablish the control/metadata connection,
> and therefore I am looking at an implementation now.

Compared to re-establishing connection, keepalive is a simpler tweak
(although having the option for both is even better...)

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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