[ovs-discuss] OVSDB Managers vs. ovsdb-server

Ben Pfaff blp at ovn.org
Fri Nov 29 16:17:20 UTC 2019


On Fri, Nov 29, 2019 at 11:54:13AM +0200, Matan Rosenberg wrote:
> I'm tying to understand what ovsdb managers actually do.
> 
> Say that I have two OVS hosts, each with its own ovs-vswitchd and
> ovsdb-server.
> Both OVS hosts are logically related, and I want to control them from a
> single, central location.
> 
> In the datapath plane, I can set-controller on all bridges on both OVS
> hosts to the same OpenFlow controller, and thus achieve central management.

OK, yes.

> In the management plane, I don't see how I can add/remove/manipulate
> bridges on both OVS hosts from the same location, since each OVS host has
> its own ovsdb-server.

That's a strange comment, since each OVS host also has its own
ovs-vswitchd, which the controller addresses individually.  The
situation for OpenFlow controllers and OVSDB managers is exactly
analogous.

> (In my use case, I happen to add/remove bridges quite frequently).
> 
> Of course, I can just issue two ovs-vctl command with different DB each
> time, but this isn't a vert scalable approach, and it also has severe
> consistency drawbacks, since the network topology is held in two places.
> This is in direct contrast from the datapath plane, because I can actually
> write an OpenFlow controller that determines the correct rules from, say,
> an application DB (not ovsdb!).

No, there's no contrast here.  The situation is exactly the same, since
the OpenFlow controller and the switch each hold the network topology
and the controller is responsible for pushing its view down to the switch.

> I've stumbled upon the ovs-vsctl set-manager command, which, from what I
> can see, can be used in conjunction with something like an OpenDaylight
> OVSDB Manager.
> If so, can a single OVSDB manager manage both OVS hosts?

Yes.

> And if so, what part does the local ovsdb-server play, if the network
> topology is held with the OVSDB manager? Do I still actually need it, or
> can ovs-vswitchd just directly query the manager?

The local ovsdb-server is the actual database.  The manager just queries
and updates it.  This is exactly the same as the OpenFlow situation.


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