Edge stacks do not support authenticating against a private registry to deploy applications stored on private registries

Issue Description

When using Edge Stacks to deploy services from a private repository, images are not able to be pulled.

Fix

Update Portainer to 2.15.0 or above.

Workaround 

Deploy a Docker registry container, put it in "cache" mode, and configure it to authenticate using your Docker Hub credentials. Locally to the edge device, it pulls from the cache locally as anonymous, but the cache knows how to retrieve from a secure repository.