examples

Example Plugin

This directory contains an example K-Rail plugin in order to allow custom written K-Rail policies for your organization that are not general purpose enough for open-source usage.

K-Rail plugins

K-Rail plugins are based on the go-plugin Hashicorp interface which runs the provided plugin executable over localhost via GRPC and protobufs. This means that theoretically any language that supports GRPC can be written as a K-Rail plugin as long as it conforms to the KRailPlugin protobuf service as seen below.

service KRailPlugin {
    rpc PluginName(PluginNameRequest) returns (PluginNameResponse);
    rpc PolicyNames(PolicyNamesRequest) returns (PolicyNamesResponse);
    rpc ConfigurePlugin(ConfigurePluginRequest) returns (ConfigurePluginResponse);
    rpc Validate(ValidateRequest) returns (ValidateResponse);
}

PluginName returns the name of the plugin as a string which is then used in the plugin_config stanza for providing customizable yaml configuration.

PolicyNames returns the names of all the policies implemented by the plugin as an array of strings which is then used to configure them under the policies stanza as enabled and report_only

ConfigurePlugin provides the customizable yaml from under corresponding plugin_config and plugin name stanza to initialize the plugin

Validate accepts the policy name with an AdmissionRequest. The resource of interest must be extracted from it. See resource/pod.go for an example of extracting PodSpecs from an AdmissionRequest. If mutation on a resource is desired, you can return a slice of JSONPatch operations and nil for the violations.

About the example

The example plugin is written in Go as a template that can be copied for your own usage with a simple example "luck_threshold" policy included. The "luck_threshold" policy rejects pods from validation based on a configurable threshold. It can be run locally with the included config.yml by using the make run-plugin command. Definitely do not use this example policy on a production cluster as it will cause frustration by rejecting 1% of pod deployments by default.