Hey so I’ve never worked with App Service but based on the docs here:
Configure a custom container - Azure App Service
Learn how to configure a custom container in Azure App Service. This article shows the most common configuration tasks. … it does seem that App Service expects your app to be listening on either port 80 or a custom configured port, and then respond to requests there.
What it seems you want to do is just run a container. Azure has a few options for that listed in the docs below:
Azure Containers—Services and Management | Microsoft Azure
Optimize your cloud application containers with Microsoft Azure. Accelerate container deployment and management with integrated tools.
You’re right though — your app would not need to be listening on a port to connect to Solace. BUT you have to be sure that wherever your app gets deployed has network access to the Solace host:port URL. Defaults for WS is 8008, WSS is 1443.