Cleat

Typed configuration for Kubernetes.

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Cleat is a configuration language whose values are JSON and whose types come from the real Kubernetes API and your CRDs. Mistakes are caught while you write, at the exact field that’s wrong, and the output is plain YAML for Argo CD, Flux, or kubectl apply.

Cleat is under active development. The language, the CLI and the editor and Argo CD integrations can change in incompatible ways, and it hasn’t been used in production yet. “Cleat” is a working name.

A taste

import * as k8s from "../schemas/kubernetes-1.37.json"

input env: "dev" | "prod"
input image: Str
input replicas: Int where self >= 1 = 2

export k8s.Deployment {
  metadata.name: "api",
  spec: {
    replicas: if env == "prod" then max(replicas, 3) else replicas,
    selector.matchLabels.app: "api",
    template: {
      metadata.labels.app: "api",
      spec.containers: [{ name: "api", image, ports: [{ containerPort: 8080 }] }],
    },
  },
}

apiVersion and kind fill themselves in. Misspell replicas, or write imagePullPolicy: "Allways", and the mistake is reported before anything reaches a cluster:

$ cleat check examples/quickstart.cleat
quickstart.cleat:13:5: error: unknown field `replcias` in `k8s.apps.v1.DeploymentSpec`; did you mean `replicas`?
quickstart.cleat:17:64: error: type mismatch: expected `"Always" | "IfNotPresent" | "Never"`, found `"Allways"`

Bad inputs are rejected before evaluation, all of them at once:

$ cleat export examples/quickstart.cleat --set env=production --set image=api:1 --set replicas=0
quickstart.cleat:6:1: error: input `env`: expected `"dev" | "prod"`, got "production" (string)
quickstart.cleat:8:1: error: input `replicas`: 0 does not satisfy `self >= 1`

Why Cleat

• Types from the real API. Import the Kubernetes OpenAPI spec and your CRD files; every resource, field, required field and enum is checked, and field documentation shows on hover.
• Typed inputs instead of values.yaml. Inputs declare their types, defaults and constraints, and bad values are rejected up front.
• Overlays that can’t silently miss. Patches are checked against the types; a misspelled field or a selector that matches nothing is an error.
• Dependencies between components become Argo CD sync waves or Flux dependsOn.
• Small and familiar. TypeScript-style structural types, ES-style imports, and no recursion or I/O, so evaluation always terminates and depends only on the repository.
• Made for editors. Completion with Kubernetes docs, hover, go to definition, errors as you type, and a live YAML preview.

Compared with