[ovs-dev] [PATCH] ovsdb: Clarify that a server that leaves a cluster may never rejoin.

[Paul Greenberg]

RAFT requires odd number of nodes. With 2 out of 4 down, there never be a majority vote.

Best Regards,
Paul Greenberg

________________________________
From: ovs-dev-bounces at openvswitch.org on behalf of Paul Greenberg <greenpau at outlook.com>
Sent: Friday, November 2, 2018 5:09 PM
To: Ben Pfaff
Cc: ovs dev
Subject: Re: [ovs-dev] [PATCH] ovsdb: Clarify that a server that leaves a cluster may never rejoin.

Hi Ben,

Let me clarify. Based on my observation, once a server loses touch with the rest of the cluster you have to rejoin it. At the same time it is not readily apparent that you have to do the clean up (removal) yourself. For example, you had a cluster of 3 nodes, then after some time one node is out. You go to that node and do a cluster join. My understanding is that a new server id gets generated.

Now, if you did not do a cleanup, you end up with 4 node cluster. When 3 out of 4 are working, there is no issue. It is almost mandatory to do a cleanup after join.

Best Regards,
Paul Greenberg

________________________________
From: Ben Pfaff <blp at ovn.org>
Sent: Friday, November 2, 2018 2:30 PM
To: Paul Greenberg
Cc: Yifeng Sun; ovs dev
Subject: Re: [ovs-dev] [PATCH] ovsdb: Clarify that a server that leaves a cluster may never rejoin.

I'm not sure what you mean. Do you mean that the commands for removing
a server from a cluster aren't documented well enough? Or something
else?

On Thu, Nov 01, 2018 at 07:03:07PM +0000, Paul Greenberg wrote:
> I would also add that when a server leaves a cluster, it must be removed using “ovs-appctl -t db.sock.ctl cluster/kick <dead-server-id>”
>
> Best Regards,
> Paul Greenberg
>
> ________________________________
> From: ovs-dev-bounces at openvswitch.org on behalf of Yifeng Sun <pkusunyifeng at gmail.com>
> Sent: Thursday, November 1, 2018 2:25 PM
> To: Ben Pfaff
> Cc: ovs dev
> Subject: Re: [ovs-dev] [PATCH] ovsdb: Clarify that a server that leaves a cluster may never rejoin.
>
> Looks good to me, thanks.
> Reviewed-by: Yifeng Sun <pkusunyifeng at gmail.com>
>
> On Mon, Oct 29, 2018 at 4:37 PM Ben Pfaff <blp at ovn.org> wrote:
>
> > This wasn't clear from the documentation.
> >
> > Reported-by; Paul Greenberg <greenpau at outlook.com>
> > Signed-off-by: Ben Pfaff <blp at ovn.org>
> > ---
> > Documentation/ref/ovsdb.7.rst | 3 +++
> > ovsdb/ovsdb-server.1.in | 3 +++
> > 2 files changed, 6 insertions(+)
> >
> > diff --git a/Documentation/ref/ovsdb.7.rst b/Documentation/ref/ovsdb.7.rst
> > index 39d85b6e5774..f891309fc05d 100644
> > --- a/Documentation/ref/ovsdb.7.rst
> > +++ b/Documentation/ref/ovsdb.7.rst
> > @@ -255,6 +255,9 @@ cluster: transactions not yet replicated to the server
> > will be lost, and
> > transactions not yet applied to the cluster may be committed. Afterward,
> > any
> > servers in its former cluster will regard the server to have failed.
> >
> > +Once a server leaves a cluster, it may never rejoin it. Instead, create
> > a new
> > +server and join it to the cluster.
> > +
> > The servers in a cluster synchronize data over a cluster management
> > protocol
> > that is specific to Open vSwitch; it is not the same as the OVSDB protocol
> > specified in RFC 7047. For this purpose, a server in a cluster is tied
> > to a
> > diff --git a/ovsdb/ovsdb-server.1.in b/ovsdb/ovsdb-server.1.in
> > index 2d80dafffb7d..9f78e87f655c 100644
> > --- a/ovsdb/ovsdb-server.1.in
> > +++ b/ovsdb/ovsdb-server.1.in
> > @@ -339,6 +339,9 @@ executed.
> > .IP
> > Use \fBovsdb\-client wait\fR (see \fBovsdb\-client\fR(1)) to wait
> > until the server has left the cluster.
> > +.IP
> > +Once a server leaves a cluster, it may never rejoin it. Instead,
> > +create a new server and join it to the cluster.
> > .
> > .IP "\fBcluster/kick \fIdb server\fR"
> > Start graceful removal of \fIserver\fR from \fIdb\fR's cluster, like
> > --
> > 2.16.1
> >
> > _______________________________________________
> > dev mailing list
> > dev at openvswitch.org
> > https://mail.openvswitch.org/mailman/listinfo/ovs-dev
> >
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