Hi Paul,
If you are "forwarding" to authoritative nameservers indeed using
stub-zone is the correct configuration as it expects to send queries to
authoritative nameservers and not resolvers. That won't help with this
issue though.
In a situation where Unbound is overwhelmed with client queries, using
'forward-no-cache: yes' (or 'stub-no-cache: yes' if you use the
stub-zone) does not help since all those queries need to be resolved.
When under client pressure, Unbound would start dropping slow queries.
Slow queries are ones that take longer than 'jostle-timeout'
(https://unbound.docs.nlnetlabs.nl/en/latest/manpages/unbound.conf.html#unbound-conf-jostle-timeout)
to resolve.
This way Unbound tries to combat Dos from slow queries or high query
rates by trying to slowly fill up the cache from fast queries that
eventually will drop the outgoing query rate and increase cache
responses. (Glocal cache responses do not contribute to the increase of
the request list).
In your case where you don't cache the upstream information, Unbound
cannot protect itself with cached answers because all the internal
upstream queries need to be resolved.
I am guessing the queries to the configured upstreams are not slower
than jostle-timeout, so not candidates to be dropped initially, but it
doesn't help that each one of them needs to always be resolved.
I would first try to use 'stub-no-cache: no' and see if the situation
gets better.
It would be possible to introduce a new configuration option per
forward/stub zone to give some kind of priority but unsure if it would
generally help or in this case in particular.
Best regards,
-- Yorgos
On 19/11/2024 03:01, Paul S. via Unbound-users wrote:
Hey team,
We run 8 node unbound clusters as recursive resolvers. The setup
forwards (using forward-zone) internal queries to a separate PowerDNS
authoritative cluster.
Recently, we've had some connectivity issues to Cloudflare (who provides
a lot of external DNS services in our environment). When this has
happened, we've seen the requestlist balloon to around 1.5-2k entries as
queries repeatedly time out.
However, the problem is that this affects forward-zones as well. We lose
resolution for internal queries when these backup events happen.
We're looking for suggestions on how to safeguard these internal
forwards. We notice stub-zone may be the more appropriate stanza for our
use case, but are unsure if that'd bypass this requestlist queuing (?)
Any thoughts greatly welcome, thank you!
Our config is fairly simple:
server:
num-threads: 4
# Best performance is a "power of 2 close to the num-threads value"
msg-cache-slabs: 4
rrset-cache-slabs: 4
infra-cache-slabs: 4
key-cache-slabs: 4
# Use 1.125GB of a 4GB node to start, but real usage may be 2.5x this so
# closer to 2.8G/4GB (~70%)
#
msg-cache-size: 384m
# Should be 2x the msg cache
rrset-cache-size: 768m
# We have libevent! Use lots of ports.
outgoing-range: 8192
num-queries-per-thread: 4096
# Use larger socket buffers for busy servers.
so-rcvbuf: 8m
so-sndbuf: 8m
# Turn on port reuse
so-reuseport: yes
# This is needed to forward queries for private PTR records to upstream
DNS servers
unblock-lan-zones: yes
forward-zone:
name: "int.domain.tld"
forward-addr: "10.10.5.5"
# No caching in unbound
forward-no-cache: "yes"
