Use Local MQTT Broker With AWS Greengrass Component

Question

I have an existing component that uses both Greengrass IPC messages, and MQTT messages, to communicate to other local components (via IPC) and AWS cloud (MQTT).

I now need to enable a messaging integration with a non-Greengrass Docker running on the same device. I was thinking of using MQTT messaging from the Greengrass Docker image, and implementing Greengrass between the two.

Could someone suggest a way of implementing this, where I could use existing AWS Greengrass resources to implement a local MQTT publisher, such that a non greengrass container can implement an MQTT subscriber and receive those messages ?

Answer

Follow-Up Clarification:

I would like to receive local messages, inside a docker container, from Greengrass. This docker container runs entirely separately and is not greengrass related, though it runs on the same device as greengrass.

What I am trying:
 - MQTT subscriber in the non-gg container (using paho mqtt in python)
 - In Greengrass:
     - Greengrass MQTT broker (EMQX) component
     - Greengrass MQTT Bridge component (configured with src: Pubsub and target: LocalMQTT)
     - Sending pubsub messages with greengrass-cli pubsub

Am I way off in my approach ? Is it possible to bridge in this way, gg IPC messages to EMQX MQTT broker ?

Answer

About the question for bridging IPC to EMQx MQTT broker, yes, you can use the MQTT Bridge component for that as you indicated. 
For sending pubsub messages, not sure why you would want to use greengrass-cli, please use the PubSub APIs: https://docs.aws.amazon.com/greengrass/v2/developerguide/ipc-publish-subscribe.html#ipc-operation-publishtotopic 
Note that the MQTT client subscriber on the non-greengrass docker image needs to be registered as an IoT Thing.

Use Local MQTT Broker With AWS Greengrass Component

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