Create docker image with non-root user

.env

USER_ID=1000

docker-compose.yml

version: '3'
services:
  web:
    build:
      context: .
      dockerfile: docker/dev/web/Dockerfile
      args:
        APP_USER_ID: $USER_ID

Dockerfile

FROM something

# linux user id for application files
ARG APP_USER_ID

# create app user
RUN useradd -d /app -u $APP_USER_ID app
USER app
WORKDIR /app