Re: [dnsdist] DoH issues after 1.8.3 -> 1.9.0 upgrade

[Remi Gacogne via dnsdist]

Hi,

On 18/03/2024 22:00, Christoph via dnsdist wrote:

This might be related:https://github.com/PowerDNS/pdns/issues/13850, not backported yet

thanks for the pointer, really looking forward to the dnsdist version
that has this solved.

Sure, I expect to release 1.9.2 including this fix in the next couple weeks.

The new nghttp2 provider for
incoming DNS over HTTPS does not support HTTP/1.1. In 1.9.x it's
still possible to switch back to the legacy h2o provider but note
that it will likely go away in the next major version of DNSdist. In
our testing the lack of HTTP/1.1 support was not an issue for actual
DNS over HTTPS clients, with most of HTTP/1.1 queries coming from
crawlers/bots, but of course we will reconsider if you find out that
legitimate DoH clients are impacted.

we see about 5-10% of non-version 2 DoH requests by looking at:

sum by (version)
(irate(dnsdist_frontend_doh_http_version_queries{job="$job"}[$__rate_interval]))

Note that this metric (doh_http_version_queries) is incremented after doing some sanity checks but before actually parsing the DNS query, so unfortunately we cannot be sure these are valid DoH queries. At this point they could be bots. Can you check doh_version_status_responses for httpversion=1 and status=200 instead?

So the practical solution to use dnsdist 1.9.0 with nghttp2 and

still support HTTP/1.1 clients is to use a webserver like nginx in front of dnsdist?

Yes, a reverse proxy like nginx or HAProxy might be the best option to keep HTTP/1.1 support at this point.

I expected an increase of this metric during our partial outage but
this value did not increase, is this expected?

irate(dnsdist_frontend_doh_version_status_responses{httpversion="1",status="400",job="$job"}[$__rate_interval])

dnsdist_frontend_noncompliantqueries also didn't increase.
Which value is expected to increase?

I'm afraid we are currently not increasing any counter in this exact case, I'll see what I can do about it.

btw:
dnsdist's v1.9.0 answer to HTTP requests not using HTTP/2:

This server implements RFC 8484 - DNS Queries over HTTP, and
requires HTTP/2 in accordance with section 5.2 of the RFC.

but RFC8484 does not actually require HTTP/2, right?

https://www.rfc-editor.org/rfc/rfc8484.html#section-5.2
 > 5.2.  HTTP/2

HTTP/2 [RFC7540] is the minimum RECOMMENDED version of HTTP for use with DoH.

It is recommended but not a "MUST".

Best regards,
--
Remi Gacogne
PowerDNS.COM BV - https://www.powerdns.com/

You are correct, but in practice I am yet to see a DoH client using HTTP/1.1 in production. Bind 9, Unbound and Knot also only support DNS over HTTP/2. That being said, I'm really open to implementing DNS over HTTP/1.1 if it serves a real purpose, I just don't want to increase the code complexity and attack surface just to reply to crawlers..

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