Add Control Bus to DSE

https://blueprints.launchpad.net/congress/+spec/dse-control-bus

Nodes participating on the data services engine (DSE) bus need a means of discovering each other and their exposed data types. Currently a periodic broadcast mechanism is used for this purpose. While effective, these broadcasts are inefficient, and complicate debugging.

Instead of using the exiting broadcast-based discovery mechanism, nodes on the DSE should publish events on a well-known “collections registry,” that every node subscribes to.

Problem description

Distribution of DSE endpoint information is currently performed using an inefficient broadcast mechanism. Instead, this information should be delivered only when changes occur, or when specifically requested.

Proposed change

• All instances of deepSix will subscribe to a well-known table, which we will refer to as the ‘collection registry’.

• When the data indexes exposed by a deepSix instance changes (including instance startup), the instance will publish an update to the collection registry.

• Each deepsix instance will maintain a list of it’s data_indexes that it has a desired subscription for. The instance will do a lookup in it’s local copy of the collection registry to find associated endpoints to send subscription requests to. As changes occur to the collection registry, each instance will re-evaluate it’s own subscriptions against these updates.

• There is a collection registry per instance of the DSE. In a hierarchical DSE, there could be multiple registries.

• The periodic broadcast of data_index information can be removed after these changes.

Alternatives

We can continue to use the existing mechanism as an alternative, but difficulties with inefficiencies and complex debugging will grow substantially as the number of nodes on the bus increases.

Policy

N/A

Policy Actions

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Data Sources

N/A

Data model impact

N/A

REST API impact

N/A

Security impact

N/A

Notifications impact

N/A

Other end user impact

N/A

Performance impact

At runtime, this change will reduce the time it takes to distribute information about new nodes in the system. It will also reduce the overall “chatter” on the bus by eliminating unnecessary broadcasts. We anticipate the reduction in chatter will greatly simplify debugging the message bus.

Other deployer impact

N/A

Developer impact

N/A

Implementation

Assignee(s)

Primary assignee:

None

Other contributors:

None

Work items

TBD

Dependencies

N/A

Testing

The existing testing framework is sufficient to test to change.

Documentation impact

N/A

References

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