I am new to docker, currently following book to learn Django. 

1. Is it necessary to be in virtual environment when running the below
command?
2. I have gone through docker basic videos which says it saves each apps as images. But where these images are saved?.
3. Does this line make the current pc root directory or dockers Image '
WORKDIR /usr/src/app'

ADD is placed before RUN in the Dockerfile.

**$ sudo docker-compose build**

But I got these errors.

```
ERROR: Service 'app' failed to build: ADD failed: stat /var/lib/docker/tmp/docker-builder912263941/config/requirements.txt: no such file or directory

```

**Dockerfile**

```
FROM python:3
RUN apt-get update \
    && apt-get install -y --no-install-recommends \
    mysql-client default-libmysqlclient-dev

WORKDIR /usr/src/app
ADD config/requirements.txt ./
RUN pip3 install --upgrade pip; \
  pip3 install -r requirements.txt
RUN django-admin startproject myproject .;\
  mv ./myproject ./origproject

```

**docker-compose.yml**

```
version: '2'
services:
  db:
    image: 'mysql:5.7'
  app:
    build: .
    command: python3 manage.py runserver 0.0.0.0:8000
    volumes:
      - './project:/usr/src/app/myproject'
      - './media:/usr/src/app/media'
      - './static:/usr/src/app/static'
      - './templates:/usr/src/app/templates'
      - './apps/external:/usr/src/app/external'
      - './apps/myapp1:/usr/src/app/myapp1'
      - './apps/myapp2:/usr/src/app/myapp2'
    ports:
      - '8000:8000'
    links:
      - db

```

**requirements.txt**

```
Pillow~=5.2.0
mysqlclient~=1.3.0
Django~=2.1.0

```