COPY command fails - docker

Question

Been stuck on this for the last 3 days. I'm building an image in a docker and
copy command fails due to not finding the right directory.
FROM python:3.6.7-alpine
WORKDIR /usr/src/app
COPY ./requirements.txt /usr/src/app/requirements.txt
RUN pip3 install -r requirements.txt
COPY . /usr/src/app
CMD python3 manage.py run -h 0.0.0.0
which is run by this docker-dev file:
version: '3.7'
services:
users:
build:
context: ./services/users
dockerfile: Dockerfile-dev
volumes:
- './services/users:/usr/src/app'
ports:
- 5001:5000
environment:
- FLASK_APP=project/__init__.py
- FLASK_ENV=development
and getting this error:
Building users
Step 1/6 : FROM python:3.6.7-alpine
---> cb04a359db13
Step 2/6 : WORKDIR /usr/src/app
---> Using cache
---> 06bb39a49444
Step 3/6 : COPY ./requirements.txt /usr/src/app/requirements.txt
ERROR: Service 'users' failed to build: COPY failed: stat /var/snap/docker/common/var-lib-docker/tmp/docker-builder353668631/requirements.txt: no such file or directory
I don't even know where to start with debugging this. When I tried to access the directory it gave me permission error. So I tried to run the command with sudo which didn't help. Any thoughts ?

Answer 1

Little late to reply, but second COPY command COPY . /usr/src/app replaces the /usr/src/app content generated by RUN pip3 install -r requirements.txt.
Try
FROM python:3.6.7-alpine
WORKDIR /usr/src/app
# install in temp directory
RUN mkdir /dependencies
COPY ./requirements.txt /dependencies/requirements.txt
RUN cd /dependencies && pip3 install -r requirements.txt
COPY . /usr/src/app
# copy generated dependencies
RUN cp -r /dependencies/* /usr/src/app/
CMD python3 manage.py run -h 0.0.0.0

Answer 2

As larsks suggests in his comment, you need the file in the services/users directory. To understand why, an understanding of the "context" is useful.
Docker does not build on the client, it does not see your current directory, or other files on your filesystem. Instead, the last argument to the build command is passed as the build context. With docker-compose, this context defaults to the current directory, which you will often see as . in a docker build command, but you can override that as you've done here with ./services/users as your context. When you run a build, the very first step is to send that build context from the docker client to the server. Even when the client and server are on the same host (a common default, especially for desktop environments), this same process happens. Files listed in .dockerignore, and files in parent directories to the build context are not sent to the docker server.
When you run a COPY or ADD command, the first argument (or all but the last argument when you have multiple) refer to files from the build context, and the last argument is the destination file or directory inside the image.
Therefore, when you put together this compose file entry:
build:
context: ./services/users
dockerfile: Dockerfile-dev
with this COPY command:
COPY ./requirements.txt /usr/src/app/requirements.txt
the COPY will try to copy the requirements.txt file from the build context generated from ./services/users, meaning ./services/users/requirements.txt needs to exist, and not be excluded by a .dockerignore file in ./services/users.

Answer 3

I had a similar problem building an image with beryllium, and I solved this deleting it into the .dockerignore
$ sudo docker build -t apache .
Sending build context to Docker daemon
10.55MB Step 1/4 : FROM centos ---> 9f38484d220f Step 2/4 :
RUN yum install httpd -y
---> Using cache ---> ccdafc4ae476 Step 3/4 :
**COPY ./**beryllium** /var/www/html COPY failed: stat /var/snap/docker/common/var-lib-docker/tmp/docker-builder04301**
$nano .dockerignore
startbootstrap-freelancer-master
run.sh
pro
fruit
beryllium
Bell.zip
remove beryllium from that file
$ sudo docker build -t apache .
Sending build context to Docker daemon 12.92MB
Step 1/4 : FROM centos
---> 9f38484d220f
Step 2/4 : RUN yum install httpd -y
---> Using cache
---> ccdafc4ae476
Step 3/4 : COPY ./beryllium /var/www/HTML
---> 40ebc02992a9
Step 4/4 : CMD apachectl -DFOREGROUND
---> Running in dab0a406c89e
Removing intermediate container dab0a406c89e
---> 1bea741cfb65
Successfully built 1bea741cfb65
Successfully tagged apache:latest