Ceph » RADOS

I might be misunderstanding your request, but we already do that on the clients:

[global]
  mon host = cephmon

and

# host cephmon
cephmon.cern.ch has address 128.142.x
cephmon.cern.ch has address 188.184.x
cephmon.cern.ch has address 128.142.x
cephmon.cern.ch has address 188.184.x
cephmon.cern.ch has address 188.184.x

I didn't try the same on OSDs, but I imagine it works just fine.

I meant for the daemons. They no longer need a mon_host in the config.

If none is found they perform a DNS lookup.

Puppet clients look up 'puppet', Salt minions look up 'salt' in the DNS search.

In Ceph's case librados or any other client could look up 'ceph-monitor' in the DNS search domain if none was configured.

Ahh OK. DNS SRV records might be better than a hardcoded hostname. See the DNS section here to see how OpenAFS does this: http://wiki.openafs.org/GettingStarted/

Dan van der Ster wrote:

Ahh OK. DNS SRV records might be better than a hardcoded hostname. See the DNS section here to see how OpenAFS does this: http://wiki.openafs.org/GettingStarted/

Yes, that is a good suggestion. SRV records serve this purpose better indeed. Used by various applications to find services in the network.

Joao Luis wrote:

Assigning this to Ricardo. He's looking into it.

Great! We might want to take this to the ceph-devel list when there is a proposal or idea.

Dan van der Ster wrote:

Ahh OK. DNS SRV records might be better than a hardcoded hostname. See the DNS section here to see how OpenAFS does this: http://wiki.openafs.org/GettingStarted/

DNS SRV records seem to serve the purpose, but what will we choose as the service name?
Maybe we can use "cephmon" or "ceph-mon". Any other suggestions?

Ricardo Dias wrote:

Dan van der Ster wrote:

Ahh OK. DNS SRV records might be better than a hardcoded hostname. See the DNS section here to see how OpenAFS does this: http://wiki.openafs.org/GettingStarted/

DNS SRV records seem to serve the purpose, but what will we choose as the service name?
Maybe we can use "cephmon" or "ceph-mon". Any other suggestions?

I would suggest "ceph-mon". Maybe we later add a new service, maybe "ceph-rgw" where RADOS Gateway Instances find neighbors. Who knows!

The recent code doesn't support IPv6, apparently. Maybe we can choose among ns_t_a and ns_t_aaaa according to conf->ms_bind_ipv6 in ceph/dns_resolve.cc. I'll be working on this in the following days, hopefully, but if someone's more familiar with this there could be less pain :)

WANG Guoqin wrote:

The recent code doesn't support IPv6, apparently. Maybe we can choose among ns_t_a and ns_t_aaaa according to conf->ms_bind_ipv6 in ceph/dns_resolve.cc. I'll be working on this in the following days, hopefully, but if someone's more familiar with this there could be less pain :)

I'm not very familiar with the code, but this sounds like a good approach.

I just stumbled across the lack of IPv6 support and created an issue for this: #23078