Same answer I wrote in the original post 
Topic summary
Deploying a custom embedded Shopify app to AWS EC2 without ngrok. The app (Node/Express + React, using the latest template) is embedded in Shopify Admin and launched via an Admin link from an order detail page; it uses the order ID to fetch customer email and redirects to an external site with query parameters. The app is running in a Docker container on EC2.
Key guidance provided:
- ngrok is not required.
- Point a valid domain to the EC2 instance.
- Use nginx to manage the domain and reverse proxy to the Shopify app.
- Configure Shopify app callback URLs to use that domain.
Open questions (no answers yet):
- Which port nginx should proxy to.
- How to start the JavaScript app (exact node command).
- Which environment variables are required and how to set them.
- Which JavaScript processes run and when.
- How to support webhooks.
Status: Partial, high-level consensus that production deployment on EC2 works without ngrok via domain + nginx + proper callback URLs. Detailed implementation steps remain unanswered; discussion is ongoing.