kube-cel

Kubernetes CEL extension functions for Rust, built on top of cel.

Implements the Kubernetes-specific CEL libraries defined in k8s.io/apiserver/pkg/cel/library and cel-go/ext, enabling client-side evaluation of CRD validation rules.

Installation

[dependencies]
kube-cel = "0.3"
cel = "0.12"

Usage

use cel::{Context, Program};
use kube_cel::register_all;

let mut ctx = Context::default();
register_all(&mut ctx);

// String functions
let result = Program::compile("'hello'.upperAscii()")
    .unwrap().execute(&ctx).unwrap();

// Quantity comparison
let result = Program::compile("quantity('1Gi').isGreaterThan(quantity('500Mi'))")
    .unwrap().execute(&ctx).unwrap();

// Semver
let result = Program::compile("semver('1.2.3').isLessThan(semver('2.0.0'))")
    .unwrap().execute(&ctx).unwrap();

CRD Validation Pipeline

With the validation feature, you can compile and evaluate x-kubernetes-validations CEL rules client-side — no API server required.

[dependencies]
kube-cel = { version = "0.3", features = ["validation"] }

use kube_cel::validation::Validator;
use serde_json::json;

let schema = json!({
    "type": "object",
    "properties": {
        "spec": {
            "type": "object",
            "properties": {
                "replicas": {
                    "type": "integer",
                    "x-kubernetes-validations": [
                        {"rule": "self >= 0", "message": "replicas must be non-negative"}
                    ]
                }
            },
            "x-kubernetes-validations": [
                {"rule": "self.replicas >= 1", "message": "at least one replica"}
            ]
        }
    }
});

let object = json!({"spec": {"replicas": -1}});

let validator = Validator::new();
let errors = validator.validate(&schema, &object, None);

assert_eq!(errors.len(), 2);
assert_eq!(errors[0].field_path, "spec");
assert_eq!(errors[1].field_path, "spec.replicas");

The validator walks the schema tree, compiles rules at each node, and evaluates them with self bound to the corresponding object value. Transition rules (referencing oldSelf) are supported by passing old_object.

Schema-aware format support

Fields with format: "date-time" or format: "duration" in the schema are automatically converted to CEL Timestamp / Duration values, matching K8s API server behavior:

let schema = json!({
    "type": "object",
    "properties": {
        "expiresAt": { "type": "string", "format": "date-time" },
        "timeout":   { "type": "string", "format": "duration" }
    },
    "x-kubernetes-validations": [
        {"rule": "self.expiresAt > timestamp('2024-01-01T00:00:00Z')", "message": "expired"},
        {"rule": "self.timeout <= duration('1h')", "message": "too long"}
    ]
});

Invalid strings gracefully fall back to Value::String.

Field name escaping

JSON field names that are CEL reserved words or contain special characters are automatically escaped when converting to CEL map keys, matching K8s API server behavior:

Supported Functions

Strings

charAt, indexOf, lastIndexOf, lowerAscii, upperAscii, replace, split, substring, trim, join, strings.quote

Lists

isSorted, sum, min, max, indexOf, lastIndexOf, slice, flatten, reverse, distinct

Sets

sets.contains, sets.equivalent, sets.intersects

Regex

find, findAll

URLs

url, isURL, getScheme, getHost, getHostname, getPort, getEscapedPath, getQuery

IP / CIDR

ip, isIP, ip.isCanonical, family, isLoopback, isUnspecified, isLinkLocalMulticast, isLinkLocalUnicast, isGlobalUnicast, cidr, isCIDR, containsIP, containsCIDR, prefixLength, masked

Semver

semver, isSemver, major, minor, patch, isGreaterThan, isLessThan, compareTo

Quantity

quantity, isQuantity, isInteger, asInteger, asApproximateFloat, sign, add, sub, isGreaterThan, isLessThan, compareTo

Format

<string>.format(<list>) with verbs: %s, %d, %f, %e, %b, %o, %x, %X

Named Format Validation

format.dns1123Label, format.dns1123Subdomain, format.dns1035Label, format.dns1123LabelPrefix, format.dns1123SubdomainPrefix, format.qualifiedName, format.labelValue, format.uri, format.uuid, format.byte, format.date, format.datetime, format.named, validate

// Returns optional: none = valid, of([...errors]) = invalid
// K8s pattern: !format.<name>().validate(value).hasValue()
let result = Program::compile("!format.dns1123Label().validate('my-name').hasValue()")
    .unwrap().execute(&ctx).unwrap();
// Value::Bool(true)

// Dynamic format lookup
let result = Program::compile("!format.named('uuid').validate('550e8400-e29b-41d4-a716-446655440000').hasValue()")
    .unwrap().execute(&ctx).unwrap();
// Value::Bool(true)

JSONPatch

jsonpatch.escapeKey

// RFC 6901: ~ → ~0, / → ~1
let result = Program::compile("jsonpatch.escapeKey('k8s.io/my~label')")
    .unwrap().execute(&ctx).unwrap();
// Value::String("k8s.io~1my~0label")

Feature Flags

All features are enabled by default. Disable with default-features = false and pick what you need:

Related

• kube-rs - Rust Kubernetes client and controller runtime
• cel - Rust CEL interpreter
• Kubernetes CEL docs

License

Apache-2.0