Re: [ClusterLabs] Minimum configuration for dynamically adding a node to a cluster

[Kristoffer Grönlund]

Jehan-Guillaume de Rorthais  writes:

> Le 8 juin 2016 13:36:03 GMT+02:00, Nikhil Utane  
> a écrit :
>>Hi,
>>
>>Would like to know the best and easiest way to add a new node to an
>>already
>>running cluster.
>>
>>Our limitation:
>>1) pcsd cannot be used since (as per my understanding) it communicates
>>over
>>ssh which is prevented.
>
> As far as i remember,  pcsd deamons use their own tcp port (not the ssh one) 
> and communicate with each others using http queries (over ssl i suppose).
>
> As far as i understand, crmsh uses ssh, not pcsd.

crmsh does use ssh but can be configured to communicate over an
alternative port in case the standard ssh port is blocked.

Cheers,
Kristoffer

>
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-- 
// Kristoffer Grönlund
// kgronl...@suse.com

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Re: [ClusterLabs] Minimum configuration for dynamically adding a node to a cluster

[Ferenc Wágner]

Nikhil Utane  writes:

> Would like to know the best and easiest way to add a new node to an already
> running cluster.
>
> Our limitation:
> 1) pcsd cannot be used since (as per my understanding) it communicates over
> ssh which is prevented.
> 2) No manual editing of corosync.conf

If you use IPv4 multicast for Corosync 2 communication, then you needn't
have a nodelist in corosync.conf.  However, if you want a quorum
provider, then expected_votes must be set correctly, otherwise a small
partition booting up could mistakenly assume it has quorum.  In a live
system all corosync daemons will recognize new nodes and increase their
"live" expected_votes accordingly.  But they won't write this back to
the config file, leading to lack of information on reboot if they can't
learn better from their peers.

> So what I am thinking is, the first node will add nodelist with nodeid: 1
> into its corosync.conf file.
>
> nodelist {
> node {
>   ring0_addr: node1
>   nodeid: 1
> }
> }
>
> The second node to be added will get this information through some other
> means and add itself with nodeid: 2 into it's corosync file.
> Now the question I have is, does node1 also need to be updated with
> information about node 2?

It'd better, at least to exclude any possibility of clashing nodeids.

> When i tested it locally, the cluster was up even without node1 having
> node2 in its corosync.conf. Node2's corosync had both. If node1 doesn't
> need to be told about node2, is there a way where we don't configure the
> nodes but let them discover each other through the multicast IP (best
> option).

If you use IPv4 multicast and don't specify otherwise, the node IDs are
assigned according to the ring0 addresses (IPv4 addresses are 32 bit
integers after all).  But you still have to update expected_votes.

> Assuming we should add it to keep the files in sync, what's the best way to
> add the node information (either itself or other) preferably through some
> CLI command?

There's no corosync tool to update the config file.  An Augeas lense is
provided for corosync.conf though, which should help with the task (I
myself never tried it).  Then corosync-cfgtool -R makes all daemons in
the cluster reload their config files.
-- 
Feri

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Re: [ClusterLabs] Minimum configuration for dynamically adding a node to a cluster

[Ken Gaillot]

On 06/08/2016 06:54 AM, Jehan-Guillaume de Rorthais wrote:
> 
> 
> Le 8 juin 2016 13:36:03 GMT+02:00, Nikhil Utane  
> a écrit :
>> Hi,
>>
>> Would like to know the best and easiest way to add a new node to an
>> already
>> running cluster.
>>
>> Our limitation:
>> 1) pcsd cannot be used since (as per my understanding) it communicates
>> over
>> ssh which is prevented.
> 
> As far as i remember,  pcsd deamons use their own tcp port (not the ssh one) 
> and communicate with each others using http queries (over ssl i suppose).

Correct, pcsd uses port 2224. It encrypts all traffic. If you can get
that allowed through your firewall between cluster nodes, that will be
the easiest way.

corosync.conf does need to be kept the same on all nodes, and corosync
needs to be reloaded after any changes. pcs will handle this
automatically when adding/removing nodes. Alternatively, it is possible
to use corosync.conf with multicast, without explicitly listing
individual nodes.

> As far as i understand, crmsh uses ssh, not pcsd.

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[ClusterLabs] Minimum configuration for dynamically adding a node to a cluster

[Nikhil Utane]

Hi,

Would like to know the best and easiest way to add a new node to an already
running cluster.

Our limitation:
1) pcsd cannot be used since (as per my understanding) it communicates over
ssh which is prevented.
2) No manual editing of corosync.conf

So what I am thinking is, the first node will add nodelist with nodeid: 1
into its corosync.conf file.

nodelist {
node {
  ring0_addr: node1
  nodeid: 1
}
}

The second node to be added will get this information through some other
means and add itself with nodeid: 2 into it's corosync file.
Now the question I have is, does node1 also need to be updated with
information about node 2?
When i tested it locally, the cluster was up even without node1 having
node2 in its corosync.conf. Node2's corosync had both. If node1 doesn't
need to be told about node2, is there a way where we don't configure the
nodes but let them discover each other through the multicast IP (best
option).

Assuming we should add it to keep the files in sync, what's the best way to
add the node information (either itself or other) preferably through some
CLI command?

-Regards
Nikhil
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