How to set working dir running web application

[pomcho555]

Environment

• OSX 10.14.2
• python3.8
• fastapi==0.63.0
• pack: 0.17.0+git-d9cb4e7.build-2045

Directory structure

my-app/
├── README.md
├── requirements.txt
├── app
│   ├── main.py
└── tests

QUESTION

I am running a web app through FastAPI and Unicorn under app directory. For the sake of using buildpacks pack, I wrote a following one liner command. But it didn't work...
I don't know how to set the working directory as the app launched. On docker, we can set WORKDIR option for that. I need some kind of similar way.

pack build sample-app --builder gcr.io/buildpacks/builder:v1 --env CNB_APP_DIR="/app"\
 --env GOOGLE_ENTRYPOINT="uvicorn main:app"

[natalieparellano]

For posterity, pack build now supports --workspace flag: Location at which to mount the app dir in the build image