[ovs-dev] OVSDB Replication: Clarifications required

[Arunkumar Rg]

Hi Andy Zhou,

Thanks for looking into this!

Please find my replies inline:

On Tue, Jul 11, 2017 at 1:30 AM, Andy Zhou <azhou at ovn.org> wrote:

> On Tue, Jul 4, 2017 at 10:52 PM, Arunkumar Rg <arunkumar.rg at gmail.com>
> wrote:
> > Hi,
> >
> > Got few clarifications on OVSDB replication. Please let me know your
> inputs
> > on it.
> >
> > 1. From the ovsdb-server code(main_loop()), it seems that the standby
> > ovsdb-server becomes 'Active' if the JSONRPC session with the
> > active-ovsdb-server is not alive.
> > Instead of this behavior, is there a way(probably some CLI option)
> wherein
> > we can instruct the ovsdb-server to not become active even if the session
> > to 'active' is not alive??
>
> It is technically possible.  What is a good use case for this?
>
*Arun:* The use case I'm looking at is - ovsdb-server runs in a VxLAN
HW-VTEP.
Now if we want to provide HW-VTEP redundancy(something like MC-LAG), then
we'll use
ovsdb-server replication in these redundant HW-VTEPs i.e ovsdb-server
running in one of the
HW-VTEPs will be acting as 'Active' and other HW-VTEP as 'standby'. With
this, the controller
will see a single HW-VTEP instead of multiple HW-VTEPs. Now, in this case,
if the HW-VTEPs
already has an inherent mechanism to call which HW-VTEP is active and which
is standby, then I want
to use that mechansim to dictate ovsdb-server to become active/standby
accordingly.

>
> > 2. I understand in the standby-ovsdb-server then no transaction(write
> > operation) can be done on it's DB. At the same time, I see an option in
> > appctl to exclude few tables from syncing, whether we can do
> > transaction(write operation) on those tables in the
> standby-ovsdb-server??
>
> This may be a good extension to current implementation.
>
*Arun:* This would be helpful for the above use case I described. I'm new
to this ovs-dev.
If you are aware, please share me on how to put this request to ovs
community.


> >
> > 3. Can the below runtime management commands of ovsdb-server can be done
> > via API calls(something like IDL APIs)??
> > ovsdb-server/connect-remote-ovsdb-server
> > ovsdb-server/disconnect-remote-ovsdb-server
> > ovsdb-server/set-sync-exclude-tables {db:table,...}
> > ovsdb-server/get-sync-excluded-tables
>
> Current design and implementation are for integration with Linux HA
> framework. Those
> extensions are technically possible. Would implementing them improve
> Linux HA integration
> better? or for supporting other HA framework?
>
*Arun:* Currently I'm trying a prototype of running a ovsdb-server on a
HW-VTEP.
For this I have written a small ovsdb-client program using the
IDL(vtep-idl).
Now I'm planning to do some prototype for HW-VTEP redundancy(as described
in my
above replies) and for this it seems to me using ovsdb-server replication
to be useful.
So if IDL has APIs for ovsdb-server replication related operations as well,
then I can
use those APIs straight away instead of calling the command lines through
system calls.

Thanks,
Arun.

> >
> > Thanks,
> > Arun.
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>