AMS to AEMaaCS Migration - Performing certain job on Publish tier

We are migrating our AEM environment from AMS to AEM as a Cloud Service (AEMaaCS). In our current production environment (AMS), we have 1 Author instance and 4 Publisher instances. One of the custom feature: Whenever a Topic is published (replicated), we need to send Topic content to an external application (from publisher only).

Currently, we compare configured sling id with 4 publisher’s sling ID and ensuring sending the content from 1 publisher only. 

After AEMaaCS migration, how we can achieve the same functionality (identify 1 pod publisher out of multi pod publishers) and then send the published content to external app from 1 pod publisher only.