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Re: Metadata over IPv6

otroan@employees.org Wed, 18 December 2019 09:35 UTC

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Subject: Re: Metadata over IPv6
From: otroan@employees.org
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Date: Wed, 18 Dec 2019 10:35:51 +0100
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>>> 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'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?

Cheers,
Ole

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