How to Edit Docker Image? - docker

Question

I did a basic search in the community and could not find a suitable answer, so I am asking here. Sorry if it was asked earlier.
Basically , I am working on a certain project and we keep changing code at a regular interval . So ,we need to build docker image everytime due to that we need to install dependencies from requirement.txt from scratch which took around 10 min everytime.
How can I perform direct change to docker image and also how to configure entrypoint(in Docker File) which reflect changes in Pre-Build docker image

Answer 1

You don't edit an image once it's been built. You always run docker build from the start; it always runs in a clean environment.
The flip side of this is that Docker caches built images. If you had image 01234567, ran RUN pip install -r requirements.txt, and got image 2468ace0 out, then the next time you run docker build it will see the same source image and the same command, and skip doing the work and jump directly to the output images. COPY or ADD files that change invalidates the cache for future steps.
So the standard pattern is
FROM node:10 # arbitrary choice of language
WORKDIR /app
# Copy in _only_ the requirements and package lock files
COPY package.json yarn.lock ./
# Install dependencies (once)
RUN yarn install
# Copy in the rest of the application and build it
COPY src/ src/
RUN yarn build
# Standard application metadata
EXPOSE 3000
CMD ["yarn", "start"]
If you only change something in your src tree, docker build will skip up to the COPY step, since the package.json and yarn.lock files haven't changed.

Answer 2

In my case, I was facing the same, after minor changes, i was building the image again and again.
My old DockerFile
FROM python:3.8.0
WORKDIR /app
# Install system libraries
RUN apt-get update && \
apt-get install -y git && \
apt-get install -y gcc
# Install project dependencies
COPY ./requirements.txt .
RUN pip install --upgrade pip
RUN pip install --no-cache-dir -r requirements.txt --use-deprecated=legacy-resolver
# Don't use terminal buffering, print all to stdout / err right away
ENV PYTHONUNBUFFERED 1
COPY . .
so what I did, created a base image file first like this (Avoided the last line, did not copy my code)
FROM python:3.8.0
WORKDIR /app
# Install system libraries
RUN apt-get update && \
apt-get install -y git && \
apt-get install -y gcc
# Install project dependencies
COPY ./requirements.txt .
RUN pip install --upgrade pip
RUN pip install --no-cache-dir -r requirements.txt --use-deprecated=legacy-resolver
# Don't use terminal buffering, print all to stdout / err right away
ENV PYTHONUNBUFFERED 1
and then build this image using
docker build -t my_base_img:latest -f base_dockerfile .
then the final Dockerfile
FROM my_base_img:latest
WORKDIR /app
COPY . .
And as my from this image, I was not able to up the container, issues with my copied python code, so you can edit the image/container code, to fix the issues in the container, by this mean i avoided the task of building images again and again.
When my code got fixed, I copied the changes from container to my code base and then finally, I created the final image.

Answer 3

There are 4 Steps
Start the image you want to edit (e.g. docker run ...)
Modify the running image by shelling into it with docker exec -it <container-id> (you can get the container id with docker ps)
Make any modifications (install new things, make a directory or file)
In a new terminal tab/window run docker commit c7e6409a22bf my-new-image (substituting in the container id of the container you want to save)
An example
# Run an existing image
docker run -dt existing_image
# See that it's running
docker ps
# CONTAINER ID IMAGE COMMAND CREATED STATUS
# c7e6409a22bf existing-image "R" 6 minutes ago Up 6 minutes
# Shell into it
docker exec -it c7e6409a22bf bash
# Make a new directory for demonstration purposes
# (note that this is inside the existing image)
mkdir NEWDIRECTORY
# Open another terminal tab/window, and save the running container you modified
docker commit c7e6409a22bf my-new-image
# Inspect to ensure it saved correctly
docker image ls
# REPOSITORY TAG IMAGE ID CREATED SIZE
# existing-image latest a7dde5d84fe5 7 minutes ago 888MB
# my-new-image latest d57fd15d5a95 2 minutes ago 888MB