Message Bus

The message bus is a simple, lightweight, and fast way to send messages between different parts (services) of your application. It’s a publish/subscribe system that allows you to send messages to a specific subject and have any listeners on that subject receive the message.

Messages

Messages are the way that data is sent between services. In the Telestion ecosystem. Messages are either JSON or binary data.

Subjects

Subjects are the way that messages are sent between services. Each subject has a name. The name is used to identify the subject.

Publish / Subscribe

The message bus is a publish/subscribe system. This means that you can publish messages to a specific subject and have any listeners on that subject receive the message.

Warning

Messages aren’t stored when using the publish/subscribe method. This means that if a service isn’t listening on a subject when a message gets published, it won’t receive the message.

If you need to ensure that a message is received, you can use the Request / Reply system to await confirmation.

Example

Here is an example of how the publish/subscribe system works:

sequenceDiagram
    accTitle: Sequence diagram of the publish/subscribe system. Text description in collapsed section below.
    participant Service A
    participant Message Bus
    participant Service B
    Service A->>Message Bus: Subscribe to subject "test"
    Service B->>Message Bus: Publish message "Hello World" to subject "test"
    Message Bus->>Service A: Message "Hello World" on subject "test"

Text Description

1. Service A subscribes to the subject “test” on the message bus
2. Service B publishes the message “Hello World” to the subject “test”
3. The message bus sends the message “Hello World” to Service A

Request / Reply

The message bus is also a request/reply system. This means that you can send a request to a specific subject and have any listeners on that subject reply to the request.

Example

Here is an example of how the request/reply system works:

sequenceDiagram
    accTitle: Sequence diagram of the request/reply system. Text description in collapsed section below.
    participant Service A
    participant Message Bus
    participant Service B
    Service B->>Message Bus: Subscribe to subject "test"
    Service A->>Message Bus: Send request "Hello World" to subject "test"
    Message Bus->>Service B: Request "Hello World" on subject "test"
    Service B->>Message Bus: Reply "Hello World" to subject "test"
    Message Bus->>Service A: Reply "Hello World" on subject "test"

Text Description

1. Service B subscribes to the subject “test” on the message bus
2. Service A sends the request “Hello World” to the subject “test”
3. The message bus sends the request “Hello World” to Service B
4. Service B replies to the request with “Hello World”
5. The message bus sends the reply “Hello World” to Service A

NATS

We use NATS as our message bus. While all other services can be replaced, the message bus is a core component of Telestion. It is the backbone of the entire system.

Authentication and Authorization

NATS also handles everything related to authentication and authorization for the message bus. You can easily control who can send and receive messages on which subjects.