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MLAND Series – Tips I – Loopback RabbitMQ Mistakes

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Purpose

The purpose of this post is to highlight the most common mistakes I experienced with Loopback and RabbitMQ myself.

Mistakes I made and might have done too

  1. Receiving [rabbit.unhandled] MessageForgotten to load mixing in model-config.json
  2. Message keep getting redelivered
  3. Getting undefined from payload

Fix Receiving [rabbit.unhandled]

This error can result from 4 different mistakes:

  • Forgotten to load mixin in model-config.json
  • Forgotten to configure component-config.json
  • Messed up the Entry in model.json
  • Connecting to Queue while not handling all Message Types

Fix Forgotten to load mixin in model-config.json

Check how the Entry for model-config.json should look like below

Fix Forgotten to configure component-config.json

Check how the Entry for component-config.json should look like below

Fix Messed up the Entry in model.json

Check how the Entry for model.json should look like below

Connecting to Queue while not handling all Message Types

If you get [rabbit.unhandled] Message of x on queue y, connection ‘default’ was not procced by any registered handlers and the messages only get re-queued and redelivered, you have probably connected an api to a queue where you receive message you don´t handle.

Loopback-rabbit-mq picks the next message available on the queues if is connected to, even if you haven´t implemented handling this messages.

So make sure you connect each api only to queues where you handle all message types from. Otherwise one API will eventually block the queue because it gets messages it can´t process.

Fix Message keep getting redelivered

Check the function you implemented and make sure you return a Promise.resolve if your function succeeded and Promise.reject if it failed.

Fix Getting undefined from payload

If the origin of your message is not loopback it might mean you need to use JSON.parse to retrieve the data in the Message. Check how the Code should look like above

Files to Look at

  1. server/model-config.json
  2. server/component-config.json
  3. common/models/model.json / server/models/model.json
  4. common/models/model.js / server/models/model.js

server/model-config.json

This file holds the Information which mixins to load for this project.

This happens inside the “mixins”: [] Block

Make sure you load the loopback-component-mq with an entry like this:

“../nodemodules/loopback-component-mq/lib/mixins”

server/component-config.json

This file holds the general configuration for components that need it.

Make sure you configure loopback-component-mq with an entry like this:

{  
   "loopback-component-mq":{  
      "path":"loopback-component-mq",
      "options":{  
         "restPort":15672,
         "acls":[  
            {  
               "accessType":"",
               "principalType":"ROLE",
               "principalId":"$unauthenticated",
               "permission":"DENY"
            }
         ]
      }
   },
   "topology":{  
      "connection":{  
         "uri":"amqp://user:password@host/vhost",
         "timeout": timeoutinmilliseconds
      },
      "exchanges":[  
         {  
            "name":"exchangename",
            "type":"exchangetype",
            "persistent":persistent
         }
      ],
      "queues":[  
         {  
            "name":"queuename",
            "subscribe":true,
            "limit":concurrentnonacknoledgedtasknumber
         }
      ],
      "bindings":[  
         {  
            "exchange":"exchangename",
            "target":"queuename",
            "keys":[  

            ]
         }
      ],
      "logging":{  
         "adapters":{  
            "stdOut":{  
               "level":5,
               "bailIfDebug":true
            }
         }
      }
   }
}

 

 

common/models/model.json / server/models/model.json

In the model.json you configure the consumers and producers that this model implements, together with which queue they operate on and which type the message has.

Make sure you configure loopback-rabbit-mq with an entry like this:

{  
   "mixins":{  
      "MessageQueue":{  
         "consumers":{  
            "nameof_function_to_imlement":{  
               "queue":"queue_name_from_component_config",
               "type":"name_of_message_type"
            }
         },
         "producers":{  
            "name_of_function_to_imlement":{  
               "exchange":"exchange_name_from_component_config",
               "options":{  
                  "routingKey":"routing_key_name",
                  "type":"name_of_message_type",
                  "contentType":"content_type_you_wish"
               }
            }
         }
      }
   }
}

 

 

common/models/model.js / server/models/model.js

In the model.js you implement the consumer and producer functions you declared i> the model.json file.

Make sure you implement it with an entry like this:

Model.name_of_function_to_implement = (payload) => {
  // If send from Loopback
  const { variable_name} = payload

  // If send from another source like python
  const { variable_name } = JSON.parse(payload)
}

If your queue needs acknowledgements make sure to return a Promise.resolve().

If something went wrong return a Promise.reject(). RabbitMQ redelivers the Message then.

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