Communication between App Services

[vijay-hcl-epl]

Hi EdgeX Team,
Currently we are exploring all the EdgeX features for one of our products. I need to know how far the communication between application services are possible. I read from this link - https://docs.edgexfoundry.org/3.0/microservices/application/ApplicationServices/ that

Application Services provide the means for data to be prepared (transformed, enriched, filtered, etc.) and groomed (formatted, compressed, encrypted, etc.) before being sent to an endpoint of choice or published back to other Application Service to consume.

I would like to understand more about "published back to other Application Service to consume."

1. Can one application service directly publish the data to other application service? I hope it is not possible and we need to use "SetResponseData" so that the data goes to message bus and then to the other application service. Please confirm.
2. If I use an app service with MQTT/HTTP/Custom trigger, then is it possible to publish the data from that service to another app service which uses Message bus trigger?
3. If I use two app services, one with HTTP trigger and another with MQTT trigger, then is it possible to share data between them?
4. Can I POST an event to core data using the api "/event/{profileName}/{deviceName}/{sourceName}" either from an application service or any external service, so that another application service with message bus trigger can read this POSTed event?

It will be helpful if you give a inline response.

Thanks in advance,
Vijay

[lenny-goodell]

@vijay-hcl-epl , you can send data to other App service in multiple ways. #1 or #2 are the prefered was. Choosing which one depends on how your data it processed. If fully process in the function pipeline, then chose #1. If combined and processed in background then choose #2.

1. Use SetResponseData to publish the data to the MessageBus using a specific topic (from config) which the other App Service is subscribed. If your data has been transformed to a custom type the other App Service must know that type and set TargetType.
   https://docs.edgexfoundry.org/3.1/microservices/application/sdk/api/AppFunctionContextAPI/#setresponsedata
   https://docs.edgexfoundry.org/3.1/microservices/application/sdk/details/TargetType/
2. Similar to above and new in EdgeX 3.1, you can use the Publish/PublishWithTopic functions to Publish the data to the MessageBus.
   https://docs.edgexfoundry.org/3.1/microservices/application/sdk/api/ApplicationServiceAPI/#publishwithtopic
   https://docs.edgexfoundry.org/3.1/microservices/application/sdk/api/AppFunctionContextAPI/#publishwithtopic
3. Export the data via Http Export function the the Http trigger of the other App Service. Same consideration for custom type as above.
   https://docs.edgexfoundry.org/3.1/microservices/application/details/Triggers/
   https://docs.edgexfoundry.org/3.1/microservices/application/sdk/api/BuiltInPipelineFunctions/#http-export
4. Use custom REST endpoints to communicate between the App Services.
   https://docs.edgexfoundry.org/3.1/microservices/application/sdk/details/CustomRestApis/

[vijay-hcl-epl]

Thank you @lenny-intel . This helps..!!