Docker: Using COPY when the Dockerfile is located in a subdirectory

All you need to do here is add context: . and dockerfile in your build section inside your docker-compose.yml file so that your service understands the complete directory structure.

# docker-compose.yml
version: "3"
services:
  webserver:
    build:
      context: .
      dockerfile: ./dockerfiles/webserver/Dockerfile
    image: webserver:php-apache