Streams

Status updates are delivered via streams.

A stream defines how status updates are delived, including:

• module and code, e.g. tlc/2
• attributes and their settings, e.g. live or update rate
• aggregation, e.g. sum or average
• default state (on/off)
• pruning, e.g. timeout

A node can have ome or more streams configured for each status type.

Unlike RSMP 3, you don’t specify subscription settings when you start fetching data. Instead you choose between the already defined streams.

graph LR
A[Service A]-->|traffic/live| Broker
A[Service A] -->|traffic/hourly| Broker
Broker-->|traffic/live| B[Manager A]
Broker-->|traffic/hourly| B[Manager A]
Broker -->|traffic/live| C[Manager B]
Broker -->|traffic/hourly| D[Manager C]

If the node allows stream administration, consumers can add/edit streams.

Receiveing data

To receive data the stream must be started and you must be subscribed to the associated topic path.

Starting and stopping a stream controls whether data is published to the associated topic path on the broker. If a stream is configured as on by default, you don’t need to manually start it.

Subscribing to the associated topic path controls whether you receive data from the broker.

Starting and Stopping

When you start a stream, it starts publishing data to broker, even if nobody has yet subscribed to the relevant topic path:

graph LR
A[Service] -->|traffic/live| Broker

Consumers must be subscribed to the relevant topic path to receive data from the broker:

graph LR
A[Service] -->|traffic/live| Broker
Broker -->|traffic/live| B[Manager]

When you stop a stream, data is no longer publishhed to the broker. Consumers will no longer receive data, even if they are still subscribed to the relevant topic path.

Stream configuration

Module and id

Identifies the status with module name, and status code id, e.g. tlc/2.

Attributes

The set of attributes to include in status updates, and their settings. For each attribute:

• Type: Send on Change, Send Along (send when other attributes change)
• Aggregation: off, count, average, median, max, min. Aggration is done according to the update rate.

Update Rate

Interval to send full updates, which are retained on the broker.

Delta Rate

Interval to send delta updates which contain only attributes that changed and are not retained on the broker.

Options:

• send on change: Delta updates are send immediately when attributes changes.
• interval: Delta update are send according to delta intervals.

Default State

A stream configured as off by default must be started before it publishes data to the broker. A stream configured as on by default starts publishing to the broker immediately after the node starts up.

Listing Streams

The node provides a list of available streams, with information about attribute set, update rate, aggregation, etc.

Stream Administration

If a node supports stream administration, remote nodes can:

• add new stream
• edit existing stream
• remove existing stream

Access to stream administration can be managed by access control lists on the broker.

Pruning

Streams can be configured to automatically stop when consumers disappear, or have been offline for a predefined period.

This is useful for streams that take up significant bandwidth, and you want to be sure that they are stopped when not used anymore.

Automatic stopping can be based on timeouts and presence message, which informs the node when other nodes go online/offline.

[To be expanded]