Fn

Functions are executables (that you can write) which accept a collection of Resource configuration as input, and emit a collection of Resource configuration as output.

Functions can be packaged as container images, starlark scripts, or binary executables.

Functions may be used to:

• Generate configuration from templates, DSLs, CRD-style abstractions, key-value pairs, etc.– e.g. expand Helm charts, JSonnet, Jinja, etc.
• Inject fields or otherwise modify configuration – e.g.add init-containers, side-cars, etc
• Rollout configuration changes across an organization – e.g.similar to https://github.com/reactjs/react-codemod
• Validate configuration – e.g.ensure organizational policies are enforced

Functions may be run at different times depending on the function and the organizational needs:

• as part of the build and development process
• as pre-commit checks
• as PR checks
• as pre-release checks
• as pre-rollout checks

Examples

# run the function defined by gcr.io/example.com/my-fn as a local container
# against the configuration in DIR
kpt fn run DIR/ --image gcr.io/example.com/my-fn

# run the functions declared in files under FUNCTIONS_DIR/
kpt fn run DIR/ --fn-path FUNCTIONS_DIR/

# run the functions declared in files under DIR/
kpt fn run DIR/

Using Functions

The [catalog] documents config functions implemented using different toolchains like starlark, typescript, and golang.

Developing Functions

See the Functions Developer Guide for more on producing functions.

Next Steps

• Learn how to run functions.
• Find out how to structure a pipeline of functions from the functions concepts page.