Maintainer Summit Europe 2025

Common Expression Language (CEL) is fast growing in adoption in the Kubernetes project with more features adding CEL support each release. Today we have CEL being used in CRD validation, validating and mutating admission policies, and is even being added in Dynamic Resource Allocation. This talk will be about CEL and all of its moving parts which you need to understand if you want to add CEL support to your feature in Kubernetes.

This talk will go into the details of how CEL works, what the apiserver/cel package adds on top of the upstream google/cel-go package such as EnvSets and DeclTypes and how we use them for integrating CEL with the Kubernetes codebase.

This talk would be useful for anyone interested in learning how CEL works and maintainers who want to add CEL support to Kubernetes - be it within the apiserver or somewhere else, like DRA. The topics covered in this talk would also be useful for maintainers who want to work with existing code in the apiserver which touches CEL.