Message Queues

In many cases, you might want to process tasks asynchronously outside of the main application flow. This is especially true for tasks that are resource-intensive or that might take a long time to complete. In such scenarios, you can leverage message queues to manage and process tasks asynchronously.

With Agnost platform queue can be RabbitMQ or Kafka as the message broker. A queue is a buffer that stores messages waiting to be processed. A producer sends messages to a queue, and a consumer reads messages from the queue and processes them. This way, tasks are decoupled from the main application flow and can be processed asynchronously, leading to better application performance and scalability.

Defining Message Queues

In your Agnost application, you can define message queues in the queue section of the Agnost-Studio;

1. In the Agnost Studio, click on the + icon located in the header to access

the options menu.

• From the dropdown menu, select Message Queue to navigate to the Message Queue section.

2. Create a New Queue

In the Message Queue section, you'll have the option to + Create Message Queue to define a new Message Queue.

3. Specify Queue Details:

A dialog box will appear, asking you to provide the following details for your new message queue:

• Message Queue Name: Enter a descriptive name for your message queue. This name should reflect the purpose or functionality of the message queue within your application.

• Specify Message Delay Duration (Optional): If you need to introduce a delay between when a message is sent and when it becomes available for processing, you can specify the message delay duration. This can be useful for scenarios where messages should not be processed immediately.

  Message Delay Feature Availability

  Please note that the ability to specify message delay duration is dependent on the capabilities of the underlying message broker, specifically RabbitMQ. If your current setup or version of RabbitMQ does not support delaying messages, this feature won't be visible or available for use. Ensure that your RabbitMQ configuration supports message delay if you intend to utilize this feature.

• Log Execution (On/Off): You can choose to log the execution of messages in this queue. Enabling this option will log detailed information about message processing, including message content, status, and execution duration.

• Select Resource from Dropdown: Choose the appropriate resource for your message queue from the dropdown menu. The resource you select should match the message broker or queue service you want to use, such as RabbitMQ or Kafka.

• Save the Queue: Click on 'Save' to create the message queue.

Creating Handler Functions

A handler function is a function that is triggered to process a message from the queue. You can create handler functions in the Agnost Studio;

Each handler function receives the message as an argument it must call once it has finished processing the message.

const queueHandler = async (message) => {
  // Process the message
  console.log("Received message: ", message)

  // Process the message and perform any necessary tasks
  // ...
}
export default queueHandler

In the example above, we've created a handler function named queueHandler that logs the received message and performs any necessary tasks.

Sending Messages to a Queue

You can send messages to a queue using the agnost.queue.submitMessage() method.

const message = {
  // The message data
}

agnost.queue.submitMessage("MoviesQueue", message, (err) => {
  if (err) {
    console.error("Failed to send message to queue:", err)
  }
})

In the example above, we've sent a message to the MoviesQueue queue. If the message fails to send, an error is logged.

Processing Messages from a Queue

When a message is sent to a queue, Agnost automatically triggers the assigned handler function to process the message. The handler function receives the message as an argument and a callback function that it must call once it has finished processing the message.

// handlers/queueHandler.js

const queueHandler = async (message) => {
  // Process the message
  console.log("Received message: ", message)

  // Process the message and perform any necessary tasks
  // ...
}
export default queueHandler

By using message queues, you can improve the performance and scalability of your Agnost applications, especially when dealing with resource-intensive or long-running tasks.