From Fragile to Resilient: ValidatingAdmissionPolicies Strengthen Kubernetes
A presentation at Cloud Native Rejekts EU 2024 in in Paris, France by Marcus Noble
In the world of Kubernetes, dynamic admission controllers have long played a pivotal role in enhancing the robustness and adaptability of clusters. For instance, the ValidatingWebhookConfiguration, which empowers users to implement intricate and finely-tuned access controls beyond the capabilities of RBAC. However, this newfound agility often comes at a price – the ease with which they can be misconfigured, potentially leading to cluster disruption and downtime.
Historically, we’ve accepted this fragility as an inevitable trade-off for greater control over our clusters. But what if we could change that narrative?
Enter ValidatingAdmissionPolicies!
In this talk we’ll take a look at what makes ValidatingAdmissionPolicies a safer choice for your validation logic and what problems they aim to solve.
We will delve into the world of ValidatingAdmissionPolicies, exploring their features and limitations. We will also draw comparisons with ValidatingWebhookConfigurations, shedding light on the problems they solve. Furthermore, I’ll provide a comprehensive walkthrough on how you can begin leveraging ValidatingAdmissionPolicies today.
Resources
The following resources were mentioned during the presentation or are useful additional information.
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KEP-3488: CEL for Admission Control
Proposal for CEL based admission control (ValidatingAdmissionPolicy)
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[KEP 3488] Promote ValidatingAdmissionPolicy to GA
Issue tracking the promotion of ValidatingAdmissionPolicy to GA, currently targetting v1.30
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Validating Admission Policy Documentation
The official documentation for using ValidatingAdmissionPolicy
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KEP-3962: Mutating Admission Policies
Proposal introducing the concept of MutatingAdmissionPolicy
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MutatingAdmissionPolicy implementation PR
The work in progress PR adding the functionality for MutatingAdmissionPolicy
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Webhooks - What’s the worst that could happen?
My talk from Rejekts in Chicago about the dangers of admission controller webhooks
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Common Expression Language in Kubernetes
The official Kubernetes documentation on CEL, including the custom functions available.
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Kyverno - Using CEL expressions
The documentation for using CEL with Kyverno policies.
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Tekton - CEL expressions
The documentation for using CEL in Tekton Triggers.
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cel-go library
The CEL Go library
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CEL Playground
An online, interactive tool for building and testing CEL expressions.
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