While exploring tooling for Kubernetes I had need for schemas to
describe the definition files, and went looking for something that
didn't require either kubectl or similar installed or even a working
Kubernetes installation.
It turns out that the OpenAPI specification contain this information, but not in a particularly usable format for tools which might just want a raw JSON Schema.
This repository contains a set of schemas for most recent Kubernetes versions. For each specified Kubernetes versions you should find four different flavours:
- vX.Y.Z - URL referenced based on the specified GitHub repository
- vX.Y.Z-standalone - de-referenced schemas, more useful as standalone documents
- vX.Y.Z-local - relative references, useful to avoid the network dependency
- vX.Y.Z-strict - prohibits properties not defined in the schema
Note that the Kubernetes API allows additional properties to be submitted,
but kubectl acts like the strict flavour above.
The schemas are now all available from kubernetesjsonschema.dev, for instance the schema for v1 of the Pod object is Kubernetes 1.14.0 is available at: kubernetesjsonschema.dev/v1.14.0-standalone/pod-v1.json
Here are the links to the deployment schemas for Kubernetes 1.14.0:
- v1.14.0/deployment.json
- v1.14.0-standalone/deployment.json
- v1.14.0-local/deployment.json
- v1.14.0-standalone-strict/deployment.json
There are lots of use cases for these schemas, they are primarily useful as a low-level part of other developer workflow tools. But at a most basic level you can validate a Kubernetes definition.
Here is a very simply example using the Python jsonschema client and an invalid deployment file:
$ jsonschema -F "{error.message}" -i hello-nginx.json v1.14.0-standalone/deployment.json
u'template' is a required property
As noted these schemas have lots of potential uses for development tools. Here are a few ideas, some of which I've been hacking on:
- Demonstrating using with the more common YAML serialisation
- Testing tools to show your Kubernetes configuration files are valid, and against which versions of Kubernetes
- Migration tools to check your config files are still valid against master or beta releases
- Integration with code editors, for instance via something like Schema Store
- Validation of Kubernetes configs generated by higher-level tools, like Helm, Ksonnet or Puppet
- Visual tools for crafting Kubernetes configurations
- Tools to show changes between Kubernetes versions
The discussion around wanting JSON Schemas for Kubernetes types has cropped up in a few places, but there are some useful comments on this issue. Joël Harkes reached a similar conclusion to the approach I ended up taking.
The tooling for generating these schemas is openapi2jsonschema. It's not Kubernetes specific and should work with other OpenAPI APIs too. This should be useful if you're using a pre-release or otherwise modified version of Kubernetes, or something like OpenShift which extends the standard APIs with additional types.