System Hooks, that allow for messaging triggered by function calls under specified conditions.

Introduction

AMQP stands for Advanced Message Queuing Protocol 1.0, which is the encoding scheme the AMQP Hooks are working with. AMQP Hooks are used to generate messages for the AMQP messaging systems whenever any relevant function is performed. They're instantiated using the URL and credentials for an existing messaging queue. The process flow itself is proceeding at the same time and can not be modified with an AMQP Hook.

Any changes to the AMQP Hook configuration require a restart of the API Gateway.

Main part(s)

This tutorial shows how to set up an AMQP system hook to generate a message when importing a document. We’ll go through an example in which we’ll configure a system hook that sends messages to a messaging system to perform an asynchronous full-text indexing (more about asynchronous full-text indexing can be found here).

Introduction

With an AMQP Hook, messages are sent to a configured messaging system using Advanced Message Queuing Protocol 1.0 (AMPQ). Where and when these messages are sent is defined in the System Hook configuration. The AMQP configuration is located in the amqp key under the systemhooks top-level key. It is represented as a list of one or more System Hooks whose parameters are described in the table below:

enable

predicate

type

url

user

password

queue

bulkSize

Configuring the AMQP System Hook

We configure an AMQP system hook to send messages to a messaging system when importing compound documents. For this we use the following configuration. Of course, a messaging system needs to support AMQP 1.0. Any changes to the AMQP Hook configuration require a restart of the API Gateway.

{
    "systemhooks": {
        "amqp": [
            {
                "enable": true,
                "predicate": "spel:(contentStreams != null && contentStreams.size() > 0 && contentStreams[0]['range'] != null && contentStreams[0]['range'].length() > 0) ? true : false",
                "type": "object.insert.document",
                "url": "127.0.0.1:5672",
                "user": "admin",
                "password": "admin_pwd",
                "queue": "lc.textextraction",
                "bulkSize": 10
            }
        ]
    }
}

For AMQP, this configuration has exactly one system hook of type object.insert.document relevant to the API-Gateway. If the evaluation of the predicate for a document on import results is true (in our example only for compound documents), the API-Gateway sends a message with the metadata of the document to the defined messaging system. In addition, the configuration specifies a bulkSize of 10, i.e. for a batch import of 100 documents matching the predicate, 10 messages with 10 metadata entries per message are written to the queue named lc.textextraction.

Activating the AMQP System Hook

In our example of asynchronous full-text indexing, the API-Gateway is responsible for evaluating the system hook. To apply the configuration, the API-Gateway must be restarted after saving the configuration file. Messages will then be send to the messaging system for the import of compound documents.

Summary

In this article, we covered the AMQP Hook configuration using the example of asynchronous full text indexing. The second type of System Hooks in yuuvis® Momentum is the Webhook.