[ovs-dev] ovsdb active backup deployment

Andy Zhou azhou at ovn.org
Thu Aug 18 18:49:52 UTC 2016


On Thu, Aug 18, 2016 at 8:34 AM, Valentine Sinitsyn <
valentine.sinitsyn at gmail.com> wrote:

> On 18.08.2016 17:42, Russell Bryant wrote:
>
>>
>> On Thu, Aug 18, 2016 at 2:30 AM, Valentine Sinitsyn
>> <valentine.sinitsyn at gmail.com <mailto:valentine.sinitsyn at gmail.com>>
>> wrote:
>>
>>     Hi everyone,
>>
>>                 Russell, Would HA manager also manage ovn-controller
>>                 switch over?
>>
>>
>>             Yes, indirectly.  The way this is typically handled is by
>>             using a virtual
>>             IP that moves to whatever host is currently the master
>>
>>         Cool, then ovn-controller does not have to be HA aware.
>>
>>
>>     In my understanding, the virtual IP feature in Pacemaker (i.e.
>>     IPaddr2) works if both active and passive nodes of the cluster are
>>     in the same IP subnet.
>>
>>     For some deployments, this would mean both nodes a located on the
>>     same physical rack. This is not actually a fault-tolerant design
>>     (think blackout).
>>
>>     If I'm getting virtual IP addresses in Pacemaker correct, wouldn't
>>     it be better to make ovn-controller HA aware? That is, have a node
>>     switching command (akin to ovsdb-server/connect-active-ovsdb-server)
>>     and let Pacemaker make use it?
>>
>>
>> I was not planning to have pacemaker manage ovn-controller on every host.
>>
> OK, makes sense.
>
> Would using a proxy server, such as HAproxy, help?

>
>>
>>     If this sounds reasonable, I can take on it probably.
>>
>>
>> In general, I think having ovn-controller able to connect to more than
>> one database IP seems fine.  I don't expect everyone to necessarily
>> agree on the same HA architecture.
>>
>> Perhaps it's simple and good enough to add some support for multiple IP
>> addresses for the southbound database that ovn-controller can rotate
>> through on reconnect attempts?
>>
> As passive ovsdb instance doesn't accept client connections, this wouldn't
> help much if the connectivity between ovn-controller and south ovsdb master
> is broken. But this scenario is likely outside current HA architecture
> either.
>

Yes, something external should change ovsdb-server from backup into
active.  A backup server accepts clinet connections, but rejects any
"write" transaction that can
change the database.

>
> In short, yes, having support for multiple IPs in ovn-controller is
> certainly a step forward in the right direction IMO.
>

I agree it could be a worthwhile feature. If we end up implementing this
feature, I hope we don't statically configure the backup server IP
address.  It may be better
for the idl client to keep track of current backup server.  One possible
way to implement it is to store the backup connection into the database.
The backup server
can issue an transaction to record its connection information, before
replicating.

>
> Best,
> Valentine
>
>
>
>> --
>> Russell Bryant
>>
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