Re: [Acme] Support for domains with redundant but not immediately synchronized servers

Michael Wyraz <michael@wyraz.de> Tue, 09 February 2016 13:53 UTC

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From: Michael Wyraz <michael@wyraz.de>
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Subject: Re: [Acme] Support for domains with redundant but not immediately synchronized servers
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Hello Jonas,
>
> > IMO a better way to support your scenario as well as those I
> > described above would be to check for an SRV-Record before checking
> > A-Records. This would be 100% compatible with existing acme http-01
> > clients. In your case you would resolve the SRV record to the
> > machine that has the acme client running on. The acme-server would
> > check for the SRV-Record for an address to lookup the challenge's
> > response at. If no SRV record is specified, it would continue with
> > A and AAAA records.
>
> I am not entirely sure I get what you want to say here. SRV records
> contain not only a host name, but also priorities, weights and ports,
> so I wonder how that information would be used in this context.
>
> Do you suggest to have the client use an SRV record to specify the
> address (including the port?) to which the server connects to complete
> the challenge? In that case, what would the effect of multiple SRV
> records for the target name be?
correct, that's exactly what I meant. Example:

_acme.http-01._tcp.mydomain.com. 3600 IN    SRV    10 1 80
acme.mydomain.com.

For multiple SRV weight/priority should be respected.

Four your case you would resolve www.mydomain.com to several ip addresses:
www.mydomain.com. IN A IP-Address-Server1
www.mydomain.com. IN A IP-Address-Server2

While acme.mydomain.com resolves to a single ip address of the server
where the acme client runs on:
acme.mydomain.com. IN A IP-Address-Server1