Kubernetes configuration without the YAMLMar 29, 2017 · 3 minute read
Tomorrow at KubeCon in Berlin I’m running a birds-of-a-feather session to talk about Kubernetes configuration. Specifically we’ll be talking about whether Kubernetes configuration benefits from a domain specific language. If you’re at the conference and this sounds interesting come along.
The fact the programme committee accepted the session proposa is hopefully a good indication that at least some other people in the community think this is an interesting topic to discuss. I’ve also had a number of conversations in person and on the internet about similar areas.
There are a number of other traces of concerns with using YAML as the main user interface to Kubernetes configuration. This comment from Brian Grant of Google on the Kubernetes Config SIG mailing list for instance:
We’ve had a few complaints that YAML is ugly, error prone, hard to read, etc. Are there any other alternatives we might want to support?
And this one from Joe Beda, one of the creators of Kubernetes:
I want to go on record: the amount of yaml required to do anything in k8s is a tragedy. Something we need to solve. (Subtweeting HN comment)
This quote from the Borg, Omega and Kubernetes paper in ACM Queue, Volume 14, issue 1 nicely sums up my feelings:
The language to represent the data should be a simple, data-only format such as JSON or YAML, and programmatic modification of this data should be done in a real programming language
This quote also points at the problem I see at the moment. The configuration and the management of that configuration are separate but related concerns. Far too many people couple these together, ultimately moving all of the management complexity onto people. That’s a missed opportunity in my view. The Kubernetes API is my favourite think about the project, I’ve waxed lyrical about it allowing for different higher-level user interfaces for different users to all interact on the same base platform. But treating what is basically the wire format as a user interface is just needlessly messy.
But what advantages do we get using a programming language to modify the data? For me it comes down to:
- Avoiding repetition
- Combining external inputs
- Building tools to enforce correctness (linting, unit testing, etc.)
- The abililty to introduce abstractions
It’s the last part I find most compelling. Building things to allow others to interact with a smaller domain specific abstraction is one way of scaling expertise. The infrastructure as code space I’ve been involved in has lots of stories to tell around different good (and bad) ways of mixing data with code, but the idea that data on it’s own is enough without higher-level abstractions doesn’t hold up in my experience.
What can I use instead?
Lukily various people at this point have build tools in this space. I’m not sure could or should be a single answer to the question (whether there should be a default is a harder question to answer) but the following definitely all show what’s possible.
- Puppet Kubernetes types
- Kotlin DSL
- Skuber (Scala DSL for Kubernetes)
Obviously I wrote one of these so I’m biased but different tools work for different people and in different contexts. For example Skuber looks nice but I mainly don’t like Scala. And I’ve been using Jsonnet for Packer templates recently with success, so I’m very interested in kubecfg which provides a nice Kubernetes wrapper to that tool.
Ultimately this is still a developing space, but compared to a year ago it is now definitely moving. For me, I hope the default for managing Kubernetes configuration slowly but surely switches away from just hand rolling data. Towards what, only time and people reporting what works for them will tell.