How to rebuild docker container in air gapped environment?

Question

I have a fastapi appplication which is to be containerised. I created the docker image from a system with internet connectivity and saved the file (tar archive). This image was loaded in a system with docker installed using docker load command which has no internet connectivity and is working fine. But now I want to make changes to the application code and rebuild the image. Only the app changes have to be pushed. How can this be achieved from this isolated system?

Answer 1

There are two actions during the build that need internet connection.

The first one is pulling the base image for your Dockerfile. So for example if your Dockerfile is something like:

FROM python:3.9

WORKDIR /code

COPY ./requirements.txt /code/requirements.txt
RUN pip install --no-cache-dir --upgrade -r /code/requirements.txt 

COPY ./app /code/app

CMD ["uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "80"]

Then you would need the python:3.9 docker image on the system. This is easily achievable by moving images using docker load as you described in the question.

The second is pip installing packages (in the previous case the step RUN pip install --no-cache-dir --upgrade -r /code/requirements.txt ). To do this install in a system with no internet connection you would need to download the .whl wheel file for each requirement and install them using --find-links /path/to/wheel/dir/ (and probably --no-index ) flags.

This can become complicated but if your dependencies are more or less fixed you can do the following:

First on the system that CAN connetc to the internet you build a base image with all your requirements:

FROM python:3.9

WORKDIR /code

COPY ./requirements.txt /code/requirements.txt
RUN pip install --no-cache-dir --upgrade -r /code/requirements.txt

Then you can build this image and load it on the system with no internet. On that you can create a new Dockerfile that starts from your newly created image and just adds your code:

FROM your-base-image

COPY ./app /code/app

CMD ["uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "80"]

Then rebuilding this image should not need any internet.