Monitoring RabbitMQ queues but handle no queue situation

Written by Claudio Kuenzler - 0 comments

Published on April 15th 2026 - Listed in Monitoring Perl Coding

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A while ago, it's been two years already, I improved the check_rabbitmq_queue and fixed a bug in this Perl coded Monitoring Plugin.

Now I ran into another issue with RabbitMQ queue monitoring: The situation of no defined queues.

No queues = Empty array

When the monitoring plugin is executed against a target RabbitMQ server (here running on localhost) without any queues, the plugin exits with an UNKNOWN error: 

ck@rmq:~$ /usr/lib/nagios/plugins/check_rabbitmq_queue.pl -H 127.0.0.1 -u user -p secret --verbose
Illegal division by zero at /usr/lib/nagios/plugins/check_rabbitmq_queue.pl line 197.

How do I know, that no queues are defined? There are two ways.

First using the rabbitmqctl command, which can be executed as root user:

root@rmq:~# rabbitmqctl list_queues
Timeout: 60.0 seconds ...
Listing queues for vhost / ...

Second - and this is used by the monitoring plugin the background - is by using the RabbitMQ API:

ck@rmq:~$ curl http://localhost:15672/api/queues -u user:secret
[]

An empty array is the response from the API. This means on this RabbitMQ server there are (currently) no queues defined.

Handling the no queue situation

I slightly modified the Perl code right after the plugin handles the response from the API. In order to catch the empty array, the array itself needs to be converted to a scalar variable and the number of elements are then read. Obviously if the number of elements inside this array is 0 (zero), then we're having this empty array (no queues) situation.

159 my $url = "";
160 if ($queue eq "all"){
161     $url = sprintf("http%s://%s:%d/api/queues%s", ($p->opts->ssl ? "s" : ""), $hostname, $port, $vhost);
162 } else{
163     $url = sprintf("http%s://%s:%d/api/queues%s/%s", ($p->opts->ssl ? "s" : ""), $hostname, $port, $vhost, $queue);
164 }
165 my ($retcode, $result) = request($url);
166 
167 # Handle empty queue list
168 if ($retcode == 200) {
169     $result =~ s/^\s+|\s+$//g;
170     if (ref($result) eq 'ARRAY' && scalar(@$result) == 0) {
171         $p->nagios_exit(UNKNOWN, "No queues found on RabbitMQ");
172     }
173 }
174 if ($retcode == 404 && $ignore) {
175     $p->nagios_exit(OK, "$result : $url");
176 }
177 if ($retcode != 200) {
178     $p->nagios_exit(CRITICAL, "$result : $url");
179 }
180 
181 my @values = ();
182 my @metrics = ("messages", "messages_ready", "messages_unacknowledged", "consumers");

New plugin output: No queues found

With that change, the plugin will now exit with state UNKNOWN (exit 3) and show in the output why: Because no queues were discovered on this RabbitMQ server.

ck@rmq:~$ ./check_rabbitmq_queue.pl -H 127.0.0.1 -u user -p secret --verbose
RABBITMQ_QUEUE UNKNOWN - No queues found on RabbitMQ

Plugin changes published

These changes have been published upstream, although the original upstream project is unfortunately dead. I also made the changes available in a new version (2.0.4) of check_rabbitmq_queue.pl in my fork on GitHub. 

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