Appreciate it! You connected dots for me. Tony
________________________________ From: Han Zhou <hz...@ovn.org> Sent: July 23, 2020 05:10 PM To: Tony Liu <tonyliu0...@hotmail.com> Cc: Han Zhou <hz...@ovn.org>; ovs-discuss <ovs-discuss@openvswitch.org> Subject: Re: [ovs-discuss] OVN: ovn-sbctl backoff On Thu, Jul 23, 2020 at 4:34 PM <tonyliu0...@hotmail.com<mailto:tonyliu0...@hotmail.com>> wrote: > > Good to know! I recall I read somewhere saying only the leader takes write > request. I will double check! > > Well, in that case, I have another question, why is such leader role > required? In a quorum based cluster, all nodes are equal. And why does > ovn-northd have to connect to the leader? > Guess I will need to read more about RAFT:) > Quick answer: only leader node does the actual write, aso all writes are redirected to leader, but it can be initiated from followers. ovn-northd connects to leader for better performance because it heavily writes. The manpage does provide more details, and yes RAFT paper has even more. > > Thanks! > > Tony > > On Jul 23, 2020 4:26 PM, Han Zhou <hz...@ovn.org<mailto:hz...@ovn.org>> wrote: > > > > On Thu, Jul 23, 2020 at 4:07 PM > <tonyliu0...@hotmail.com<mailto:tonyliu0...@hotmail.com>> wrote: > > > > Thanks Han for the prompt responses! > > That option is ok for reading. If I want to write, I have to connect to the > > leader, right? Then my question remains, how does ovn-sbctl find out how to > > connect to the leader? > > > > RAFT doesn't require you to connect to leader for writing. You can connect to > any node and write. > However, if for any reason you want to connect to the leader, you need to > specify the DB connection method as: <server1>,<server2>,...,<serverN>. For > example: > tcp:10.0.0.2:6641<http://10.0.0.2:6641>,tcp:10.0.0.3:6641<http://10.0.0.3:6641>,tcp:10.0.0.4:6641<http://10.0.0.4:6641>. > You can read more details about OVSDB clustering in manpage ovsdb(7). > > Thanks, > Han > > > Thanks again! > > > > Tony > > > > On Jul 23, 2020 3:57 PM, Han Zhou <hz...@ovn.org<mailto:hz...@ovn.org>> > > wrote: > > > > > > > > On Thu, Jul 23, 2020 at 3:43 PM Tony Liu > > <tonyliu0...@hotmail.com<mailto:tonyliu0...@hotmail.com>> wrote: > > > > > > Hi, > > > > > > In case of ovsdb cluster, when I run ovn-sbctl, it connects to the unix > > > socket of local sb-db. > > > If local sb-db is not the leader, ovn-sbctl tries another server to look > > > for the leader. > > > How does ovn-sbctl connect to another server? By which connection? > > > How does ovn-sbctl know the connection? > > > Or the local sb-db asks to be the leader to respond ovn-sbctl? > > > I can't figure out how it works from verbose messages. > > > Any help to clarify is appreciated! > > > > > > > > > Thanks! > > > > > > Tony > > > > If you don't intentionally try to connect to the leader, you can use > > ovn-sbctl --no-leader-only ... to avoid the retry. > > If you want to avoid typing this option every time, you can export > > OVN_SBCTL_OPTIONS"="--no-leader-only", and then just run ovn-sbctl ... > > (does this answer your question?) > > > > Thanks, > > Han > > > > > >
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