CODEWITHSUNDEEP
pythondockerloggingdocker-compose
Tabita
Tabita

Reputation: 13

Permission denied when python app tries to write log file into shared volume in docker

I'm trying to write a simple python application to run inside docker with non-root user and I want to log into a shared volume the log files.

docker-compose.yml

version: '3.7'

services:
  testapp:
    hostname: pythonapp
    container_name: pythonapp
    build:
      context: .
      dockerfile: Dockerfile
    environment:
      - TZ=Europe/Rome
    ports:
      - "8080:8080"
    volumes:
      - ./log:/home/pythonapp/src/log

docker build file

FROM python:3

# set environment variables
ENV PYTHONDONTWRITEBYTECODE 1
ENV PYTHONUNBUFFERED 1

# Create a user with given UID.
RUN useradd -m -u 5000 pythonapp
USER pythonapp
RUN id

RUN mkdir -p /home/pythonapp/src/log
RUN chown -R pythonapp:pythonapp /home/pythonapp 
WORKDIR /home/pythonapp/src

## copy from host to container files
COPY --chown=pythonapp:pythonapp . .

## install dependencies
RUN pip install --user --upgrade pip
RUN pip install --user -r requirements.txt

CMD ["python", "/home/pythonapp/src/pythonapp.py", "-p", "8080"]

Before building the image I created log folder in host macchine.

mkdir log
ls -la
>>> drwxrwxr-x 2 tabita tabita 4096 ott  2 19:16 log

setfacl -m u:5000:rwx ./log

ls -la
>>> drwxrwxr-x+ 2 tabita tabita 4096 ott  2 19:16 log

getfacl log/
>>># file: log/
# owner: tabita
# group: tabita
user::rwx
user:5000:rw-
group::rwx
mask::rwx
other::r-x

Then I created the image using docker-compose

docker-compose -f docker-compose.yml up --build -v

However, I get error here

pythonapp | /home/pythonapp/src
pythonapp | pythonapp
pythonapp | uid=5000(pythonapp) gid=5000(pythonapp) groups=5000(pythonapp)
pythonapp | Traceback (most recent call last):
pythonapp |   File "/home/pythonapp/src/ssh_honeypot.py", line 28, in <module>
pythonapp |     logging.basicConfig(
pythonapp |   File "/usr/local/lib/python3.9/logging/__init__.py", line 2003, in basicConfig
pythonapp |     h = FileHandler(filename, mode,
pythonapp |   File "/usr/local/lib/python3.9/logging/__init__.py", line 1146, in __init__
pythonapp |     StreamHandler.__init__(self, self._open())
pythonapp |   File "/usr/local/lib/python3.9/logging/__init__.py", line 1175, in _open
pythonapp |     return open(self.baseFilename, self.mode, encoding=self.encoding,
pythonapp | PermissionError: [Errno 13] Permission denied: '/home/pythonapp/src/log/pythonapp.log'
pythonapp exited with code 1

DEBUGGING

I tried to get into the container and create a file in the log folder. I'm able to create one but from host system I can't see the created file.

Could you please help me?

Upvotes: 1

Views: 3357

Answers (1)

Etienne Dijon
Etienne Dijon

Reputation: 1303

I've tried your files with this script :

# pythonapp.py
with open('/home/pythonapp/src/log/test.txt', 'w') as f:
    f.write("Hello world!")

It works very well only if x access is granted to user 5000.

this permission is needed to go through log directory.

Regarding your output, permissions are currently rw-

getfacl log/
>>># file: log/
...
user:5000:rw-
...

As your procedure seemed exact, could you try again from this :

log is under my working directory

  1. Add rights for user with UID:5000: 
    setfacl -m u:5000:rwx log
  2. Check rights, rwx is required

    I think --tabular is a good option to view ACL permissions

    getfacl --tabular log 
# file: log
USER   <myuser>  rwx     
user   5000      rwx     
GROUP  <myuser>  rwx     
mask             rwx     
other            r-x
  3. pythonapp.py should be able to write under log directory:

    docker-compose up --build

    Step 13/13 : CMD ["python", "/home/pythonapp/src/pythonapp.py", "-p", "8080"]
 ---> Using cache
---> fcd2afb9f961
Successfully built fcd2afb9f961
Successfully tagged so_testapp:latest
Starting pythonapp ... done
Attaching to pythonapp
pythonapp exited with code 0

Upvotes: 2

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