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Spotlight on SIG CLI

Author: Arpit Agrawal

In the world of Kubernetes, managing containerized applications at scale requires powerful and efficient tools. The command-line interface (CLI) is an integral part of any developer or operator’s toolkit, offering a convenient and flexible way to interact with a Kubernetes cluster.

SIG CLI plays a crucial role in improving the Kubernetes CLI experience by focusing on the development and enhancement of kubectl, the primary command-line tool for Kubernetes.

In this SIG CLI Spotlight, Arpit Agrawal, SIG ContribEx-Comms team member, talked with Katrina Verey, Tech Lead & Chair of SIG CLI,and Maciej Szulik, SIG CLI Batch Lead, about SIG CLI, current projects, challenges and how anyone can get involved.

So, whether you are a seasoned Kubernetes enthusiast or just getting started, understanding the significance of SIG CLI will undoubtedly enhance your Kubernetes journey.


Arpit: Could you tell us a bit about yourself, your role, and how you got involved in SIG CLI?

Maciej: I’m one of the technical leads for SIG-CLI. I was working on Kubernetes in multiple areas since 2014, and in 2018 I got appointed a lead.

Katrina: I’ve been working with Kubernetes as an end-user since 2016, but it was only in late 2019 that I discovered how well SIG CLI aligned with my experience from internal projects. I started regularly attending meetings and made a few small PRs, and by 2021 I was working more deeply with the Kustomize team specifically. Later that year, I was appointed to my current roles as subproject owner for Kustomize and KRM Functions, and as SIG CLI Tech Lead and Chair.


Arpit: Thank you! Could you share with us the purpose and goals of SIG CLI?

Maciej: Our charter has the most detailed description, but in few words, we handle all CLI tooling that helps you manage your Kubernetes manifests and interact with your Kubernetes clusters.

Arpit: I see. And how does SIG CLI work to promote best-practices for CLI development and usage in the cloud native ecosystem?

Maciej: Within kubectl, we have several on-going efforts that try to encourage new contributors to align existing commands to new standards. We publish several libraries which hopefully make it easier to write CLIs that interact with Kubernetes APIs, such as cli-runtime and kyaml.

Katrina: We also maintain some interoperability specifications for CLI tooling, such as the KRM Functions Specification (GA) and the new ApplySet Specification (alpha).

Current projects and challenges

Arpit: Going through the README file, it’s clear SIG CLI has a number of subprojects, could you highlight some important ones?

Maciej: The four most active subprojects that are, in my opinion, worthy of your time investment would be:

  • kubectl: the canonical Kubernetes CLI.
  • Kustomize: a template-free customization tool for Kubernetes yaml manifest files.
  • KUI - a GUI interface to Kubernetes, think kubectl on steroids.
  • krew: a plugin manager for kubectl.

Arpit: Are there any upcoming initiatives or developments that SIG CLI is working on?

Maciej: There are always several initiatives we’re working on at any given point in time. It’s best to join one of our calls to learn about the current ones.

Katrina: For major features, you can check out our open KEPs. For instance, in 1.27 we introduced alphas for a new pruning mode in kubectl apply, and for kubectl create plugins. Exciting ideas that are currently under discussion include an interactive mode for kubectl delete (KEP 3895) and the kuberc user preferences file (KEP 3104).

Arpit: Could you discuss any challenges that SIG CLI faces in its efforts to improve CLIs for cloud-native technologies? What are the future efforts to solve them?

Katrina: The biggest challenge we’re facing with every decision is backwards compatibility and ensuring we don’t break existing users. It frequently happens that fixing what's on the surface may seem straightforward, but even fixing a bug could constitute a breaking change for some users, which means we need to go through an extended deprecation process to change it, or in some cases we can’t change it at all. Another challenge is the need to balance customization with usability in the flag sets we expose on our tools. For example, we get many proposals for new flags that would certainly be useful to some users, but not a large enough subset to justify the increased complexity having them in the tool entails for everyone. The kuberc proposal may help with some of these problems by giving individual users the ability to set or override default values we can’t change, and even create custom subcommands via aliases

Arpit: With every new version release of Kubernetes, maintaining consistency and integrity is surely challenging: how does the SIG CLI team tackle it?

Maciej: This is mostly similar to the topic mentioned in the previous question: every new change, especially to existing commands goes through a lot of scrutiny to ensure we don’t break existing users. At any point in time we have to keep a reasonable balance between features and not breaking users.

Future plans and contribution

Arpit: How do you see the role of CLI tools in the cloud-native ecosystem evolving in the future?

Maciej: I think that CLI tools were and will always be an important piece of the ecosystem. Whether used by administrators on remote machines that don’t have GUI or in every CI/CD pipeline, they are irreplaceable.

Arpit: Kubernetes is a community-driven project. Any recommendation for anyone looking into getting involved in SIG CLI work? Where should they start? Are there any prerequisites?

Maciej: There are no prerequisites other than a little bit of free time on your hands and willingness to learn something new :-)

Katrina: A working knowledge of Go often helps, but we also have areas in need of non-code contributions, such as the Kustomize docs consolidation project.