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While your correct that a chassis replacement can avoid data rebalancing in the FQDN case if you update DNS, you can actually do the same today with the IP-based system. You can use the set_info command of swift-ring-builder to change the IP for existing devices and this avoids any rebalancing in the cluster.

--John



On Jul 23, 2014, at 6:27 PM, Osanai, Hisashi <osanai.hisashi at jp.fujitsu.com> wrote:

> 
> I would like to discuss this topic more deeply.
> 
> I understand we need to prepare DNS systems and add a lot of operational 
> complexity and burden to use the DNS system when we use FQDN in Ring files.
> 
> However I think most datacenter have DNS systems to manage network resources 
> such as ip addresses and hostnames and it is centralized management.
> And you already pointed out that we can get benefit to use FQDN in Ring files 
> with some scenarios. 
> 
> A scenarios: Corruption of a storage node
> 
> IP case:
> One storage node corrupted when swift uses IPs in Ring files. An operator removes 
> the node from swift system using ring-builder command and keeping the node for 
> further investigation. Then the operator tries to add new storage node with 
> different ip address. In this case swift rebalance all objects.
> 
> FQDN case:
> One storage node corrupted when swift uses FQDN in Ring files. An operator prepares 
> new storage node with difference ip address then changes info in DNS systems with 
> the ip address. In this case swift copy objects that related to the node.
> 
> If above understanding is true, it is better to have ability for using FQDN in Ring 
> files in addition to ip addresses. What do you think?
> 
> On Thursday, July 24, 2014 12:55 AM, John Dickinson wrote:
> 
>> However, note that until now, we've intentionally kept it as just IP
>> addresses since using hostnames adds a lot of operational complexity and
>> burden. I realize that hostnames may be preferred in some cases, but this
>> places a very large strain on DNS systems. So basically, it's a question
>> of do we add the feature, knowing that most people who use it will in
>> fact be making their lives more difficult, or do we keep it out, knowing
>> that we won't be serving those who actually require the feature.
> 
> Best Regards,
> Hisashi Osanai
> 
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