Requirements.txt to be installed once for the first time when the env is created and when there ar changes made init

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1

Hi,
I have created a docker file like below(only half part is given) , the issue am facing is whenever i commit t , the “&& apk add --no-cache python3 py3-pip tini mysql-dev and venv new_env is being created and requirements.txt” is also running each and every time so deployment time is getting more and more. i want my env to be created once and if there are any changes made in requirements.txt file then it should be installed(only the last updated one). how to create that dockerfile. help with this.

FROM alpine:latest

WORKDIR /app

COPY . .

RUN set -xe \
    && apk add --no-cache python3 py3-pip tini mysql-dev mariadb-dev python3-dev gcc musl-dev 
    && python3 -m venv new_env \
    && source new_env/bin/activate \
    && pip install --upgrade pip setuptools-scm \
    && pip3 install -r requirements.txt \
   etc....,.....
 CMD ["/app/new_env/bin/python3", "/app/manage.py", "runserver", "0.0.0.0:8000"]
2

'Im not sure I understand the question.I assume you have a problem with the image layer caching and the RUN instruction is always invalidated. You can learn about image layer caching and Dockerfile optimization here:

I also edited your question.

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3

Dear rimelek,

I hope this message finds you well. I am reaching out to discuss a concern related to the Docker image building process for our project.

Currently, our Dockerfile builds the image by installing both system and software dependencies with each code commit. While this ensures a consistent environment, it has raised concerns about the efficiency of the build process.

Specifically, I am looking to optimize the Docker build to leverage caching effectively. My goal is to streamline the process so that, if there are no changes in the requirements.txt file, the build process utilizes the cache instead of reinstalling all dependencies repeatedly.

To provide some context, here is a snippet of our current Dockerfile:


FROM alpine:latest

WORKDIR /app

COPY . .

RUN set -xe \
    && apk add --no-cache python3 py3-pip tini mysql-dev mariadb-dev python3-dev gcc musl-dev linux-headers libffi-dev openssl-dev g++ geos \
    && python3 -m venv new_env \
    && source new_env/bin/activate \
    && pip install --upgrade pip setuptools-scm \
    && pip3 install -r requirements.txt 

CMD ["/app/new_env/bin/python3", "/app/manage.py", "runserver", "0.0.0.0:8000"]

I believe that by optimizing the structure of the Dockerfile and strategically placing instructions, we can achieve the desired caching behavior. This would significantly improve the build time, especially during code commits that don’t involve changes to the dependencies.

I would appreciate your insights and suggestions on how we can achieve this optimization effectively.

Thank you for your time and consideration. I look forward to discussing this further and implementing improvements to our Docker build process.

4

I shared a link to the documentation which discusses exactly what you need. Have you checked that? I wouldn’t repeat the documentation, but if you read it and you have a specific question, you can always ask about that too.

Your COPY instruction is the first and you copy everything, so of course you invalidate the cache every time you change anything. Install the common dependencies, then copy the txt file, run the pip install, and copy the rest of the files with COPY . .. Don’t forget to use .dockerignore or you could copy something you don’t want.

I would also note that what you do with the pip commands would not be recommended even without container. Use pip or pip3, but not both at the same time. The rest of it is container-related

  • I wouldn’t install python in an image, although you can do that and I wouldn’t say it’s bad, but you could just use the official Python images and choose the Alpine variant if you prefer that.
  • I know, pip can complain about running without virtual env, but I wouldn’t create a virtual environment in an already isolated environment. Python developers feel free to correct me, but here is a tutorial from the Docker blog: Containerized Python Development - Part 1 | Docker
  • Even if you use a virtual environment, you can just set the PATH environment variable the same way the sourcable script would do it, but you can do it in the Dockerfile:
    ENV PATH="/app/new_env/bin:$PATH"
    or simply use the python command as you did in the CMD instruction:
    RUN /app/new_env/bin/python3 -m pip install --upgrade pip setuptools-scm
  • If we are talking about cache, we also have to talk about pip cache, whiich you don’t need in the container, so run the pip command with the --no-cache-dir flag, so your image could be smaller.
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