[mosquitto-dev] What are these errors?

[Travis Griggs <travisgriggs@xxxxxxxxx>]

My broker (2.0.14 from the ppa) running on Ubuntu 20.04.2 LTS (Focal Fossa) at Rackspace, is frequently reporting lines like the following in the systemd journal:

  mosquitto[674]: warning: /etc/hosts.allow, line 39: can't verify hostname: getaddrinfo(pin-064-185-102-178.static.pocketinet.com, AF_INET) failed

The ip addresses vary. Sometimes they're just onesie/twosies, sometimes they come in bursts. I typically have 100-400 clients publish/subscribed. They use TLS.

I do have a custom authentication plugin, but it just validates user/pass against topic patterns.

A local sysadmin says these are just reverse dns lookup errors. And thinks they are benign. Are they? If they are benign, why are they even in there? Or is there something I should be changing in my configuration? My configuration looks like:

$ cat /etc/mosquitto/mosquitto.conf
# Place your local configuration in /etc/mosquitto/conf.d/
#
# A full description of the configuration file is at
# /usr/share/doc/mosquitto/examples/mosquitto.conf.example

#persistence true
#persistence_location /var/lib/mosquitto/

log_dest file /var/log/mosquitto/mosquitto.log

include_dir /etc/mosquitto/conf.d

AND

$ cat /etc/mosquitto/conf.d/*.conf
listener 8883
capath /etc/ssl/certs
certfile /etc/letsencrypt/live/this_host/fullchain.pem
keyfile /etc/letsencrypt/live/this_host/privkey.pem
#allow_anonymous true
allow_anonymous false
auth_plugin /etc/mosquitto/conf.d/custom_authplugin.so
log_timestamp_format %Y-%m-%dT%H:%M:%S
log_type all
connection_messages true

Line 39 of the /etc/hosts.allow is just
ALL : 50.56.142. # Rackspace Cloud Monitoring

Thanks for any help. I've been using MQTT/mosquitto for about 4 years now to facilitate ag automation, and I love it.