Services/MessageQueuing

Overview

The Message Queue project is part of Project Sagrada , providing a service for applications to queue messages for clients.

The first version of the MQ will focus on providing a useful service for the Notifications project to enqueue messages for many queues and for clients to poll for messages on a given queue.

No message aggregation is done in this version, if a client needs to get messages for more than one subscription it must poll each queue and aggregate them.

The first version could be considered a Message Store rather than a queue as it supports a much richer set of query semantics and does not let public consumers remove messages. Messages can be removed via the entire queue being deleted by the App or by expiring.

Project

Engineers

• Ben Bangert

User Requirements

• Service App can create queues
• Service App can add messages to queue
• Messages on queues expire
• Clients may read any queue they are aware of

Proposed API

For the first version, applications allowed to use the Message Queue will be given an application key that must be sent with every request, and their IP must be on an accepted IP list for the given application key.

Internal Apps

POST /queue/new

   Creates a new queue, takes the queue name as POST param queue_name.

DELETE /queue/{queue_name}

   Deletes a given queue created by the App.

POST /queue/{queue_name}/clear

   Clears the given queue of all messages, without deleting it.

POST /queue/{queue_name}

   Create a message on the given queue. Contents is expected to be
   a JSON object.
   
   Raises an error if the queue does not exist.

Clients

GET /queue/{queue_name}

   Returns all messages for the queue. Can optionally be passed
   one of several query parameters:
       
       since_timestamp - All messages newer than this timestamp
       limit           - Only return N amount of messages
   
   Messages are returned in order of newest to oldest.

Use Cases

Notifications

The new version of Notifications will use the MQ to store messages for users from various websites and allow users to poll the MQ directly for new notifications they have allowed.

• Internal app add's messages to a queue by queue name
• Internal app can delete queues by name
• Devices can read a queue by name
• Devices can read the X most recent messages
• Devices can read messages since XXX
• Messages are encoded as JSON