Re: Metadata over IPv6

[[e-mail]]

Brian,

>>>>> Is you problem solvable using "service discovery" (e.g. DNS-SD)?
>>> 
>>> It *might* be, but I can't guarantee DNS will always be present, so it would be better to have a well-known address.  Typically this part of initialization in a cloud image is done in cloud-init, which is right after DHCP completes, and the address it uses is hard-coded in the binary itself to make things simple.
>>> 
>>> That's not to say mDNS couldn't be used, but having to deploy something in order to do a single lookup for 'metadata.local' could add a lot of overhead since there could be thousands of private networks involved, each with it's own daemon.
>> We have been around the "service discovery" block a few times. Not one of the industry's proudest moments.
>> Not to rehash all the alternatives here.
>> If I understand you correctly, the problem you like to solve is "How can I find the Openstack(?) provisioning URL for this link?".
> 
> I'd have to ask specifics of the cloud-init maintainers, but from what I know and can glean from source code it wants a url:
> 
> DEF_MD_URL = "http://169.254.169.254"
> 
> This can vary depending on the cloud, and each image for a specific cloud will have a "baked-in" url for this.
> 
>> I'm little uneasy about reserving a well-known interface-id/address for the purpose. Isn't it a layer violation? I'm just a little concerned about collectivily taking the cost too. And scale as well, if lots of "applications" are required to be provisioned this way.
>> There are probably 10-15 ways of doing it.
>> If you do DHCP anyway, why couldn't the URL be passed as an option in DHCP?
> 
> Yes, there are many ways to do this, it all seems to rely on a well-known link-local address being reachable though.  I'm reluctant to suggest a DHCP option since it will add complexity since more parts will needed to be changed to support it.

At the top of this email you stated: "...which is right after DHCP completes".

Cheers,
Ole