From Newbie to Core Contributor: My Journey with CNCF Sealer

I am Zhou Xinyuan, a soon‑to‑be graduate student who studied Docker‑based network security during my undergraduate years and later joined Alibaba's Sealer core runtime development as a sealer member.

Sealer is an open‑source cluster‑image tool from Alibaba that enables one‑click Kubernetes cluster installation, helping Docker users transition smoothly to Kubernetes.

Why Sealer Became My Focus

It is a CNCF Sandbox project, offering a clear growth path from sandbox to graduated status.

Its innovative “cluster image” concept extends Docker‑image convenience to entire clusters via a Kubefile.

The project presents many open challenges documented in its RoadMap and Issues, providing ample contribution opportunities.

Overcoming the Initial Hurdles

As a newcomer I struggled with Git basics, issue filing, and pull‑request creation. I learned to combine the official documentation, README, and source code to understand Sealer’s architecture, especially the runtime module and cluster‑image design.

First Issue and First Pull Request

My first issue highlighted the high coupling of the runtime module and limited support for K0s, K3s, and K8s extensions. The community responded positively and invited me to improve the code, leading to a two‑week research and refactor effort.

The first PR involved fixing the GitHub Issue template and required handling DCO signature checks and commit rebasing before finally being merged after three attempts.

Integrating into the Community

Sealer holds bi‑weekly maintainer meetings where contributors discuss features and bugs. I presented my runtime design draft, received feedback, and gradually became comfortable speaking in meetings.

Practical Demo: Building a K3s Cluster Image

FROM k3s:v1.24.1
COPY imageList manifests

Using a Kubefile, you can package an application into a cluster image and launch a K3s cluster with sealer run.

Runtime Refactor Experience

After mastering the contribution workflow, I focused on refactoring the runtime module. I evaluated multiple installers (kubeadm, K0s, K0sctl, K3s‑install), abstracted common interfaces, and added unit tests. Challenges included choosing the right installer, unifying cluster actions, configuring image registries, and creating K0s/K3s cluster images.

During my research I drafted diagrams of installer comparisons; one such diagram is shown below.

Guidance for New Open‑Source Contributors

Effective ways to get involved include following a project's RoadMap, fixing bugs you encounter, or submitting issues and PRs. Writing a concise self‑introduction email and maintaining communication with maintainers also accelerates integration.

Conclusion

Open source is a collaborative, innovative practice that offers both opportunities and risks. By progressing from a user to an issue reporter and finally a contributor, I gained confidence in Git, Kubernetes, and cloud‑native tooling, and I look forward to seeing Sealer’s ecosystem grow.