Message Queues - andrewkyllo-401-advanced-javascript/seattle-javascript-401d34 GitHub Wiki

Message Queues

• A queue server runs independently and is tasked with routing events and messaging between clients.
• Any connected client can "publish" a message into the server
• Any connected client can "subscribe" to receive messages by type
• The Queue server has the ability to see which clients are connected, to which queues they are attached and further, to which events they are subscribed
• The queue server is tasked with receiving any published message and then distributing it out to all connected and subscribed clients.

What is a message?

• A package of information, categorized by queue and event
• queue - which general bucket does this message belong
• event - What event has happened
• payload - data associated with the event

Real Time vs Queued Messaging

• Real time messages are broadcasted to users whether they are logged in or not.
• A true queue will keep track of the deliver status of every event/message.
• Any broad cast that is not received will remain in the queue until it cane be delivered.

Use Case

• An API server responds to a POST request

  • User's access rights are confirmed

  • The data is analyzed and normalized

  • The data is sent to the database for saving

  • The database publishes a message into the queue

    • Queue: DB
    • Event: CREATE
    • Payload: JSON Object containing the created record

  • The API server sends information back to its client as normal