How to configure Galera Arbitrator (garbd)

[Владислав Андреевич]

Good day! I have 3 servers, the first and second set "Percona XtraDB Cluster". Please help to establish Galera Arbitrator (garbd) on a third server. (to avoid problemmy "split brain" in two northern regions). I was trying to do (with a third server): garbd-a gcomm :/ / ip_adres: 3400-g cluster0

But the operation began and ended with what to do next I do not know. Thanks in advance!

[Ilias Bertsimas]

Hello,

If you are looking for an example on how to start garbd with the most common options here's one: garbd -d -a gcomm://ip_of_a_synced_cluster_node:port(4567 default) -g cluster0 (name of the cluster) -o "include within the double quotes the same wsrep_provider_options you have on the other 2 nodes".

You can remove -d to run it in foreground and debug garbd in case it does not become part of the cluster.

Also you can read more about it on http://www.codership.com/wiki/doku.php?id=galera_arbitrator (wiki currently down for some reason).

Kind Regards,

Ilias.

[SyRenity]

Hi,

Is it possible to point garbd to two nodes (in two node deployment):
garbd -d -a gcomm://IP1, IP2 -g cluster0

And have it synch with the one that currently up?

Thanks.

[SyRenity]

Also, how to connect the nodes back to garbd?

Just adding it's IP in the end of wsrep_urls does not works as the node tries to get the state from garbd, and shuts down.

Thanks.

[Will Holmes]

Id like more info on this too

[Alex Yurchenko]

On 2013-11-11 15:26, SyRenity wrote:
> Also, how to connect the nodes back to garbd?
>
> Just adding it's IP in the end of wsrep_urls does not works as the node
> tries to get the state from garbd, and shuts down.
>
> Thanks.
>
> On Monday, November 11, 2013 3:24:37 PM UTC+2, SyRenity wrote:
>>
>> Hi,
>>
>> Is it possible to point garbd to two nodes (in two node deployment):
>> garbd -d -a gcomm://IP1, IP2 -g cluster0
>>
>> And have it synch with the one that currently up?
>>
>> Thanks.
>>

1) Come on! ;) You already have a command line (albeit with a stray
space in the address list), why don't just hit it?

2) garbd is not a full-fledged node. It can help with quorum or message
relaying, but it does not have a state. So if it is the last man
standing, you don't want to connect to it - it is likely to be of no
use, especially if it saw a more advanced node before: it knows that the
joiner is out of date, but it can't help it in any way. If it is not the
last one, then there is no point to connect to it as well: there are
other nodes.

So, no, you don't connect your nodes to garbd, only the other way
around. And so you don't put its address into wsrep_cluster_address
list.

Regards,
Alex

--
Alexey Yurchenko,
Codership Oy, www.codership.com
Skype: alexey.yurchenko, Phone: +358-400-516-011

[SyRenity]

Hi,

Thanks for the explanation, I also learned it the hard way, when nodes pointed to garbd refused to come up.
Also, I presume the message garb shows "WARN: 1 (node1): State transfer to 0 (garb) failed: -1 (Operation not permitted)" is a expected as exactly it does not hold state, correct?

So the configuration should be as follows:

Node1 - configured with gcomm:// (only the old style works for me for some reason)
Node2 - joins Node1
Garbd - points to both of Nodes

Btw, if the nodes are not pointed to garbd, how does then it participates in quorum selections?

Thanks.

[Alex Yurchenko]

Well, garbd is pointed to the nodes, right? Which also means that in
some rare cases (like graceful shutdown of both nodes) garbd will be
left alone and needs to be restarted.

> Thanks.