[Bug 1668771] Re: systemd-resolved negative caching for extended period of time

[Drew Freiberger]

This affects bionic openstack cloud environments when os-*-hostname is
configured for keystone, and the keystone entry is deleted temporarily
from upstream dns, or the upstream dns fails providing no record for the
lookup of keystone.endpoint.domain.com.

We have to then flush all caches across the cloud once DNS issue is
resolved, rather than auto-healing at 60 seconds as if we were running
nscd with negative-ttl set to 60 seconds.

Ultimately, a negative TTL that is settable would be ideal, or the
ability to not cache negative hits would also be useful.  Only
workaround now is to not use caches or to operationally flush caches as
needed.

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https://bugs.launchpad.net/bugs/1668771

Title:
  systemd-resolved negative caching for extended period of time

Status in systemd:
  New
Status in systemd package in Ubuntu:
  Confirmed

Bug description:
  231-9ubuntu3

  If a DNS lookup returns SERVFAIL, systemd-resolved seems to cache the
  result for very long (infinity?). I have to restart systemd-resolved
  to have the negative caching purged.

  After SERVFAIL DNS server issue has been resolved, chromium/firefox
  still returns DNS error despite host can correctly resolve the name.

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