For short:1. Dockerfile is for building image only, the image is buit prior to start a instance on Beanstalk, so there is no env. available2. The SH script is called when start a instance on beanstalk, where the env is available.

It's a common trick to solve the problem: Let's clarify why adding a shell script (build-and-serve-app.sh) in the Docker build process is necessary, particularly in the context of making the SHOPIFY_API_KEY available during the build of your frontend...