Using Docker to update and commit to a container image

I was helping a customer build some customized automation tasks using vRealize Automation Codestream. These tasks required the use of a container image with certain tools installed, usually we can include aCI task to download the tools into the container image on the fly. However, my customer’s environment is offline, so I needed to provide them a container image with everything installed by default.

Before we dive into the process of running a container and committing the changes, it is recommended where possible to create a new docker file that would build your docker image as needed with the associated commands such as the below:

FROM node:12-alpine
RUN apk add --no-cache python g++ make
WORKDIR /app
COPY . .
RUN yarn install --production
CMD ["node", "src/index.js"]

Committing changes to a container image in this way can cause the image to become bloated. But sometimes there’s a need to do just do it this way.

Prerequisites

• Docker installed

Pull the image you want to update

docker pull {image location/name}

Check your images and get the ID

docker images

For the next command, we will need the Image ID.

Run your image as an active container

docker run -it {Image_ID} /bin/bash

This will then drop you into the tty of the running container.

Modify your container

As an example for this blog post, I am installing net-tools package. Typically, I wouldn’t install this tools package into a container. Where needed, I would use busyboxand it’s tools when troubleshooting in a container environment.

apt install net-tools

Clean up/tmp and apt download files location as needed.

Exit out of your container.

Get your container ID

docker ps -a

Commit your container image changes

docker commit {container_id} {tag}

In my example, I’ve included in my tag a version number as well.

Saving your image for a manual import elsewhere

docker save {image_name:tag} > {filename}.tar

# To compress your image further
docker save {image_name:tag | gzip > {filename}.tar.gz

Pushing your image to a repository

You can now push this new commit to your repository, the following example will push to DockerHub.

Log into your repository as necessary.

docker login {server_address} --username {username} [--password]/[--password-stdin]

To push your image:

docker push {image name/tag}

# Example
docker image saintdle/k8s-ci:0.1

Regards

Follow @Saintdle

Dean Lewis

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