warning prometheus alert for rabbitmq queue space left

[Ciocoiu Petrisor]

Can you help me with Prometheus expression alert that can monitor the space left of a specific rabbitmq queue?

For example, I have couple of rabbitmq queues with "x-max-length-bytes"= 115747500 bytes"

# rabbitmqctl -p v-host list_queues name arguments | grep 115747500

 queue-test1 [{"x-max-length-bytes",115747500 }] 
 queue-test2 [{"x-dead-letter-exchange",[]},{"x-message-ttl",604800000},{"x-max-length-bytes",115747500 }] 
 queue-test3 [{"x-max-length-bytes",115747500 }] 
 queue-test4 [{"x-dead-letter-exchange",[]},{"x-message-ttl",604800000},{"x-max-length-bytes",115747500 }] 
 queue-test5 [{"x-max-length-bytes",115747500 }] 
 queue-test6 [{"x-dead-letter-exchange",[]},{"x-message-ttl",604800000},{"x-max-length-bytes",115747500 }] 

 # rabbitmqctl -p v-host list_queues 

 test1 471 

 test2 4163 

 test3 0 

 test4 2466 

 test5 0 

 test6 0

I found on the google that the max_message_size for Rabbitmq is 32768 bytes, so I thought if I can have the below math expression:

(max_message_size(32768 bytes) * number queue messages) - x-max-length-bytes ( 115747500 bytes) = total_space_left_in_queue_bytes if total_space_left_in_queue_bytes > 90% = send warning