Pulsar Docker images are currently based on Ubuntu base images. While these images has served us well in the past years, there are few shortcomings.
Alpine Linux is a Linux distribution designed explicitely to work well in container environments and has strong focus on security and a minimalistic set of included depedendencies.
Ubuntu images come with a much larger set of pre-installed tools. In many cases these are not actually needed by Pulsar, and it‘s better not include anything in the container images unless it’s strictly required.
Example of minimal image size:
$ docker images | egrep 'ubuntu|alpine' alpine 3.19 1dc785547989 4 days ago 7.73MB ubuntu 22.04 031631b93326 11 days ago 69.3MB
Similarly, also the packaged that can be installed in Alpine are generally much smaller than the corresponding Ubuntu packages. In a complex image like the Pulsar one, this quickly adds up to hundreds of MBs.
Comparison between the 2 base images with only the Java runtime added (JRE):
alpine-jre latest eb0e093ee71c 29 seconds ago 211MB ubuntu-jre latest 4147e1b2c6d1 7 seconds ago 377MB
Size of Docker images is very important, because these images end up being stored in many registries and downloaded a million of times, bringing a concern in costs for network transfer as well as for storage. Additionally, in many cases how fast is an image to download will determine the time it takes to spin up a new container in a new virtual machines (eg: when scaling a cluster up in response to a traffic increase).
By starting with a minimal set of pre-installed tools, Alpine reduces the surface for security issues in the base image.
At this moment there are 12 Medium/Low CVEs opened in Ubuntu for which there is no resolution available. Some of these CVEs have been opened for many months. Even though these CVEs don't look particularly dangerous and might not apply in 100% of cases to the Pulsar deployment, they will still be flagged in every security review, and they will trigger an in-depth investigation and require ad-hoc approvals.
At the same time, there are 0 CVEs in the Alpine image.
~ docker scout quickview ubuntu:22.04
! New version 1.2.2 available (installed version is 1.0.9) at https://github.com/docker/scout-cli
✓ SBOM of image already cached, 143 packages indexed
Target │ ubuntu:22.04 │ 0C 0H 2M 10L
digest │ 031631b93326 │
~ docker scout quickview alpine:3.19.0
! New version 1.2.2 available (installed version is 1.0.9) at https://github.com/docker/scout-cli
✓ SBOM of image already cached, 19 packages indexed
Target │ alpine:3.19.0 │ 0C 0H 0M 0L
digest │ 1dc785547989 │
Convert the tooling that produces the Pulsar Docker image to use Alpine as the
As part of this PIP there will be no explicit work to reduce the size of the Docker image, other than the conversion of the base image. This could be done as part of further initiatives.
The base of apachepulsar/pulsar will be converted to use Alpine Linux base image. All the other images that are part of the Pulsar projects will be updated to make sure they can work correctly (eg: use apk add instead of apt install).
Release notes for Pulsar 3.X.0 release will include note to notify downstream users, who might be doing some advanced customizations to the official Apache Pulsar images. This should be a tiny minority of users though. In most cases, users will see no visible change, and will not have to perform any extra step of configuration change during the upgrade from an Ubuntu based image to an Alpine based image.
No changes
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No compatibility problems.
No difference from a regular upgrade.