Shiny issues reading from AWS RDS

I have a Shiny application that reads data from a Postgres table in AWS Redshift and when running locally, works fine. When I try and publish the app, it publishes fine but when the page renders, the data never loads. The connection is set up using a config.yml file where I define my server/host, user, password, and port. In the dbConnect statement, I use RPostgreSQL::PostgreSQL() for the driver from the DBI package. Am I missing something obvious here? I even tried hardcoding the parameters for a test instance but no luck. All the application is doing in this case is getting the data with a dbGetQuery and then displaying the data using renderDataTable.

It might be a firewall issue. Have you published your app on shinyapps.io?