Helm CEL Plugin

A Helm plugin that uses Common Expression Language (CEL) to validate values. Instead of using JSON Schema in values.schema.json, you can write more expressive validation rules using CEL in values.cel.yaml.

Installation

helm plugin install https://github.com/idsulik/helm-cel

Usage

Create a values.cel.yaml file in your chart directory alongside your values.yaml file:

rules:
  - expr: "has(values.service) && has(values.service.port)"
    desc: "service port is required"
  
  - expr: "values.service.port >= 1 && values.service.port <= 65535"
    desc: "service port must be between 1 and 65535"
  
  - expr: "!(has(values.replicaCount)) || values.replicaCount >= 1"
    desc: "if replicaCount is set, it must be at least 1"

Then run validation:

helm cel /path/to/your/chart

Example

Given this values.yaml:

service:
  type: ClusterIP
  port: 80

replicaCount: 1

image:
  repository: nginx
  tag: latest

And this values.cel.yaml:

rules:
  - expr: "has(values.service) && has(values.service.port)"
    desc: "service port is required"
  
  - expr: "values.service.port >= 1 && values.service.port <= 65535"
    desc: "service port must be between 1 and 65535"
  
  - expr: "values.replicaCount >= 1"
    desc: "replica count must be at least 1"
  
  - expr: |
      has(values.image) && 
      has(values.image.repository) && 
      has(values.image.tag)
    desc: "image repository and tag are required"

If validation fails, you'll get a clear error message:

❌ Validation failed: replica count must be at least 1
   Rule: values.replicaCount >= 1
   Path: replicaCount
   Current value: 0

Writing Validation Rules

Each rule in values.cel.yaml consists of:

• expr: A CEL expression that should evaluate to true for valid values
• desc: A description of what the rule validates

CEL expressions have access to the entire values structure through the values variable. Some useful CEL functions:

• has(values.path) - checks if a field exists
• type(value) - returns the type of a value
• size(list) - returns the length of a list or map

Common Validation Patterns

1. Required fields:

- expr: "has(values.fieldName)"
  desc: "fieldName is required"

2. Value constraints:

- expr: "values.number >= 0 && values.number <= 100"
  desc: "number must be between 0 and 100"

3. Conditional requirements:

- expr: "!(has(values.optional)) || values.optional >= 0"
  desc: "if optional is set, it must be non-negative"

4. Type validation:

- expr: "type(values.ports) == list"
  desc: "ports must be a list"

5. Complex object validation:

- expr: |
    has(values.container) && 
    has(values.container.image) && 
    has(values.container.tag)
  desc: "container must have image and tag"

Development

Requirements:

• Go 1.20 or later

Build:

make build

Install locally:

make install

Run tests:

make test

Contributing

1. Fork the repository
2. Create your feature branch (git checkout -b feature/amazing-feature)
3. Commit your changes (git commit -m 'Add some amazing feature')
4. Push to the branch (git push origin feature/amazing-feature)
5. Open a Pull Request

License

Distributed under the MIT License. See LICENSE for more information.