Docker Debian nc command not found

Question

When I build my Debian image from docker-compose, with the command $ docker-compose -f docker-compose-dev.yml build web, like so:

docker-compose-fev.yml

services:

  web:
    build:
      context: ./services/web
      dockerfile: Dockerfile-dev
    volumes:
      - './services/web:/usr/src/app'  
    ports:
      - 5001:5000
    environment:
      - FLASK_ENV=development
      - APP_SETTINGS=project.config.DevelopmentConfig
      - DATABASE_URL=postgres://postgres:postgres@web-db:5432/web_dev 
      - DATABASE_TEST_URL=postgres://postgres:postgres@web-db:5432/web_test
      - SECRET_KEY=my_precious
    depends_on:  
      - web-db
      - redis

As though it appears to build all packages successfully, I'm getting:

web_1| /usr/src/app/entrypoint.sh: 5: /usr/src/app/entrypoint.sh: nc: not found

If I change #!/bin/sh to #!/bin/bash, error log changes:

web_1| /usr/src/app/entrypoint.sh: line 5: nc: command not found

Dockerfile:

FROM python:3.7-slim-buster

RUN apt-get update && apt-get -y dist-upgrade
RUN apt-get -y install build-essential libssl-dev libffi-dev libblas3 libc6 liblapack3 gcc python3-dev python3-pip cython3
RUN apt-get -y install python3-numpy python3-scipy 

# set working directory
WORKDIR /usr/src/app

COPY ./requirements.txt /usr/src/app/requirements.txt 
RUN pip3 install -r requirements.txt

# add entrypoint.sh
COPY ./entrypoint.sh /usr/src/app/entrypoint.sh

RUN chmod +x /usr/src/app/entrypoint.sh

# add app
COPY . /usr/src/app

# run server
CMD ["/usr/src/app/entrypoint.sh"]

entrypoint.sh

#!/bin/sh

echo "Waiting for postgres..."

while ! nc -z web-db 5432; do
  sleep 0.1
done

rm -rf celery_logs/*

echo "PostgreSQL started"

python manage.py run -h 0.0.0.0

---

Note: this entrypoint configuration used to work with Alpine, and now has changed to Debian.

what am I missing?

Nickola

nc: command not found is the actual error – Dissension

yes. I am trying to install apt-get install -y netcat. still building. – Nickola

By the way, this image works great. github.com/tiangolo/meinheld-gunicorn-flask-docker – Dissension

numpy and scipy should be installed with pip, and python3 has pip already, so don't need python3-pip – Dissension

you mean in requirements.txt as well, or in Dockerfile? – Nickola

feel free to update Dockerfile code in order to improve it, like you said. either on an answer os in the question itself. I'd approve – Nickola

@cricket_007 I have some other scientific packages in requirements.txt, like pandas, matplotlib, scikitlearn. do you recommend me to move numpy ans scipy there too? – Nickola

Move whatever you need to run the app within requirements file, yes – Dissension

Answer 1

Update the Dockerfile and append,

RUN apt install -y netcat

It should be like,

FROM python:3.7-slim-buster


RUN apt-get update && apt-get -y dist-upgrade
RUN apt-get -y install build-essential libssl-dev libffi-dev libblas3 libc6 liblapack3 gcc python3-dev python3-pip cython3
RUN apt-get -y install python3-numpy python3-scipy 
RUN apt install -y netcat

Windrow

I had done RUN apt-get update && apt-get -y dist-upgrade && apt-get install -y netcat. any different? – Nickola

No difference, it would install nc! and are you still experiencing the same issue? – Windrow

Its not really best practice to have multiple RUN lines like that – Dissension

@cricket_007 you mean that could add additional layers to the image? – Windrow

It will, yes. Also, rm the apt cache – Dissension

If the apt-get update gets cached but it's a week old, the apt-get install lines can fail (both Debian and Ubuntu fairly aggressively purge non-current packages from their repositories). It's important to apt-get update && apt-get install in the same RUN command to avoid this. ("Additional layers" isn't really a significant concern on its own.) – Ceramic

@Data docs.docker.com/develop/develop-images/… – Dissension

@cricket_007 rm -rf /var/lib/apt/lists/* after the last RUN apt-get? – Nickola

@DataGarden I think apt-get clean will do the same, you can run apt-get -s clean to do a simulation and see what are the locations will be cleared. – Windrow

@AnuradhaFernando" Official Debian and Ubuntu images automatically run apt-get clean, so explicit invocation is not required.". From the link above. – Nickola