README.md

Pub Sub Service Source Code

This folder contains the source code for the Pub Sub Service. The service provides publishing applications with the ability to dynamically create and manage topics and get messaging broker information.

Messaging Broker

The Pub Sub Service was designed with flexibility in mind, allowing for a different messaging broker to be used, if desired. To use a different messaging broker, a broker connector implementing the PubSubConnector trait needs to be created (see the mosquitto broker connector for an example).

See Bring Your Own Broker for a list of requirements.

If a different broker is to be used and it doesn't meet the above requirements, please reach out to us via a github issue and we can provide assistance with the integration!

Topic Management

The service provides publisher applications with dynamic topics and management while allowing the publishers to maintain full control over the lifetime of the created topics.

The service enables this control for publishers in several ways:

Topic Creation

The service provides a gRPC method CreateTopic (see pubsub.proto) for publishers to generate a topic to use. The service returns the generated topic name and message broker connection information. The publisher can then use this information to start publishing on this created topic.

Topic Updates

When a publisher requests for a topic to be created, they provide a management callback uri. This is used by the Pub Sub Service to inform the publisher of events happening on the topic. Specifically, the service notifies the publisher when the following actions happen:

• START: There are zero subscribers on a topic, and a subscribe event occurs.
• STOP: There is one subscriber on a topic, and an unsubscribe event occurs.

  NOTE: This is also used if a topic has no subscribers for a period of time and a topic still exists. This is planned to be separated out into a TIMEOUT action.

The publisher controls the lifetime of the topic so it is free to ignore these messages. It provides the publisher with an easy way to determine when to start, stop or delete a dynamically created topic.

Topic Deletion

The service provides a gRPC method DeleteTopic (see pubsub.proto) for publishers to delete a topic that was generated through the service. This removes the topic from the active topics list and sends a topic deletion message to all subscribers of the topic, to inform those applications that there will not be any more messages over that topic.

Running the Pub Sub Service with Chariott

The service can be run on its own or with Eclipse Chariott. The way the service interacts with Chariott is through registering itself as a provider that can be discovered through the Chariott service. Publishers then communicate with Chariott to get connection information to the service and directly communicate.

Configure Pub Sub Service to use Chariott

1. Copy the pub_sub_service_settings.yaml template to .agemo/config if the file does not already exist. From the enlistment root, run:

   cp ./config/template/pub_sub_service_settings.yaml ./.agemo/config/

2. Uncomment and set the following values:

   # The URI that the Chariott service listens on for requests.
   # Example: "http://0.0.0.0:50000"
   chariott_uri: "http://0.0.0.0:50000"
   
   # The namespace of the Pub Sub service.
   # Example: "sdv.pubsub"
   namespace: "sdv.pubsub"
   
   # The name of the Pub Sub service.
   # Example: "dynamic.pubsub"
   name: "dynamic.pubsub"

   This will override the default configuration and tell the service to interact with Chariott. see config overrides for more information.

Run the Pub Sub Service with Chariott

One can see an example of a publisher and subscriber interacting with Chariott and the Pub Sub Service in the Chariott Enabled Samples, but to simply run the service and have it attempt registration with Chariott, run the following command in the enlistment's root once the above configuration has been set:

cargo run -p pub-sub-service