Previously we would return a detailed errorString, which ProblemDetailsFromDNSError
would turn into a generic, uninformative "Server failure at resolver".
Now we return a new internal dnsError type, which ProblemDetailsFromDNSError can
turn into a more informative message to be shown to the user.
This provides a means to add retries to DNS look ups, and, with some
future work, end retries early if our request deadline is blown. That
future work is tagged with #1292.
Updates #1258
This moves the RTT metrics calculation inside of the DNSResolver. This
cleans up code in the RA and VA and makes some adding retries to the
DNSResolver less ugly to do.
Note: this will put `Rate` and `RTT` after the name of DNS query
type (`A`, `MX`, etc.). I think that's fine and desirable. We aren't
using this data in alerts or many dashboards, yet, so a flag day is
okay.
Fixes#1124
Moves the DNS code from core to dns and renames the dns package to bdns
to be clearer.
Fixes#1260 and will be good to have while we add retries and such.
Jacob Hoffman-Andrews