Introduction

Why?

There are a number of excellent message bus implementations available, all with different features. What makes this different?

The distinguishing feature of this message bus is it's support for select feed publishers. Typically a message bus implements a broadcast feed (e.g. RabbitMQ, Redis, etc). The source publishes messages on topics while clients subscribe to topics of interest to them.

In a select feed the publisher gets notified when a client subscribes or unsubscribes from a topic. This allows the publisher to only publish data that is being listened to, and also to send an initial image to the new subscriber, after which it publishes deltas to all subscribers.

Pros

The notification capability provides a number of useful features:

• It reduces network bandwidth by only sending messages that clients have requested.
• It allows for dynamic messaging. For example a client may request AAPL.2020-01-01/2020-02-01 to get prices for the given range.

Cons

As all messages pass through a single broker, this beccomes a processiong bottleneck.

Other Feastures

There are a number of other features provided:

• SSL transport
• Authentication: LDAP, JWT, and password file.
• Authorization. The server can be configured to only send data for which the client is authorized.