Gluster users - May 2021 - Geo-replication adding new master node

Hello,

We have a GlusterFS configuration with mirrored nodes on the master side
geo-replicating to mirrored nodes on the secondary side.

When geo-replication is initially created it seems to automatically add all
the mirrored nodes on the master side as geo-replication master nodes,
which is fine. My first question is, if we add a new master side node how
can we add it as a geo-replication master?
This doesn't seem to happen automatically, according to the output of
"gluster volume geo-replication gvol0 secondary::gvol0 status". If we
use
the normal "gluster volume geo-replication gvol0 secondary::slave-vol
create push-pem force" it says that the secondary side volume is not empty,
which is true because we're adding a master node to the existing
geo-replication.

My second question is whether we can geo-replicate to multiple nodes on the
secondary side? Ideally we would normally have something like:
master A -> secondary A
master B -> secondary B
master C -> secondary C
so that any master or secondary node could go offline but geo-replication
would keep working.

Thank you very much in advance.

-- 
David Cunningham, Voisonics Limited
http://voisonics.com/
USA: +1 213 221 1092
New Zealand: +64 (0)28 2558 3782
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Hi David,
> On 31-May-2021, at 10:37 AM, David Cunningham <dcunningham at
voisonics.com> wrote:
> 
> Hello,
> 
> We have a GlusterFS configuration with mirrored nodes on the master side
geo-replicating to mirrored nodes on the secondary side.
> 
> When geo-replication is initially created it seems to automatically add all
the mirrored nodes on the master side as geo-replication master nodes, which is
fine. My first question is, if we add a new master side node how can we add it
as a geo-replication master?
> This doesn't seem to happen automatically, according to the output of
"gluster volume geo-replication gvol0 secondary::gvol0 status". If we
use the normal "gluster volume geo-replication gvol0 secondary::slave-vol
create push-pem force" it says that the secondary side volume is not empty,
which is true because we're adding a master node to the existing
geo-replication.
This is not automatic. Run `gluster-georep-sshkey generate` and georep create
push-pem with force option to push the keys from new nodes to secondary nodes.

You can also try this tool instead of georep create command.

https://github.com/aravindavk/gluster-georep-tools
<https://github.com/aravindavk/gluster-georep-tools>

$ gluster-georep-setup gvol0 secondary::slave-vol --force
> 
> My second question is whether we can geo-replicate to multiple nodes on the
secondary side? Ideally we would normally have something like:
> master A -> secondary A
> master B -> secondary B
> master C -> secondary C
> so that any master or secondary node could go offline but geo-replication
would keep working.
Geo-replication command needs one Secondary node to establish the session. Once
session starts, Geo-rep starts one worker process per master brick.

These worker processes gets the list of secondary nodes by running the `ssh
<secondary-host> gluster volume info <secondary-volume>`. Then
Geo-rep distributes the secondary nodes connection in round robin way. For
example, if Master volume contains three nodes and secondary volume 3 nodes as
you mentioned then Geo-rep makes connection as Master A -> Secondary A,
Master B -> Secondary B and Master C -> Secondary C.

Secondary node failover: If a node goes down in secondary cluster then Master
worker connects to other secondary node and continues replication. One known
issue is if the secondary node specified in the Geo-rep create command goes down
then it fails to get the Volume info(To get list of secondary nodes). This can
be solved by providing the list of secondary nodes as config(Not yet available).
> 
> Thank you very much in advance.
> 
> -- 
> David Cunningham, Voisonics Limited
> http://voisonics.com/ <http://voisonics.com/>
> USA: +1 213 221 1092
> New Zealand: +64 (0)28 2558 3782
> ________
> 
> 
> 
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> 
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Aravinda Vishwanathapura
https://kadalu.io



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