Updating a Docker Image

We use docker containers for CI/CD build purposes at work. We had an instance recently where our container needed some added applications in order to publish the build artifacts up and out to a web server for future download. Here is how we went about updating our docker container.

To start I logged into the container VM using Putty. Could do this with console (vmware) or via SSH.

List images on the machine to find the image you want to edit.

docker images
REPOSITORY                    TAG               IMAGE ID       CREATED         SIZE
sphinx_base_2                 latest            77af0a8bf8bd   45 hours ago    951MB
<none>                        <none>            83eba990b65c   46 hours ago    946MB
gitlab/gitlab-runner-helper   x86_64-943fc252   9996479d93d9   4 months ago    66.8MB
gitlab/gitlab-runner-helper   x86_64-6214287e   c463142b7af1   11 months ago   57.2MB
sphinx_base_1                 latest            b14e6de4b12a   13 months ago   840MB
gitlab/gitlab-runner-helper   x86_64-c5874a4b   fdd135c22836   13 months ago   57.6MB
alpine                        latest            f70734b6a266   13 months ago   5.61MB

Start up a new container with the image we want to update.

docker run -d -it sphinx_base_2

List the running containers

docker ps
c6c9b2cf63f9   sphinx_base_2   "/bin/sh"   38 seconds ago   Up 37 seconds             admiring_kilby

Log into the console for that container. This example is for Alpine Linux.

docker exec -it c6c9b2cf63f9 /bin/sh

Install the apps using the package manager. This example is for Alpine Linux. Notice how the console changes to indicate that we are working inside the container.

/ # apk add openssh sshpass rsync

Test out the app’s functionality in the running container.

/ # rsync test example

If everything checks out commit the changes to the image. You can commit to the same image name (copies overtop) or to a new image name (version control).

docker commit c6c9b2cf63f9 sphinx_base_2

That is the quick synopsis for modifying a docker container.