Kubernetes Jsonnet Controller

This controller lets you use Jsonnet to template your custom resources. It also provides an event handler system for create, modify, and delete events on your custom resources. These handlers are also Jsonnet templates, but they are intended to be short-lived resources, such as Jobs that run a maintenance script to update metrics, send emails, notify a code repository, etc. whenever a custom resource is modified in your cluster.

Create a watches.json file with something like so

[
  {
    "resource": "mycustomresource",
    "directory": "mycustomresource-dir"
  }
]

and create a directory named mycustomresource-dir. Inside it, create a manifest.jsonnet file that returns an array of objects (to be compatible with Jsonnet's YAML output). This will be executed to determine the manifest of resources the cluster should create for your custom resource. It will be given two external variables: name and spec. name is the string name in .metadata.spec on the custom resource. spec is the JSON-encoded .spec data on the custom resource. Its values can be obtained with

local spec = std.parseJson(std.extVar('spec'));

Add any number of *.jsonnet files to oncreate, onchange, and ondelete directories placed in mycustomresource-dir. These will be templated and passed to kubectl apply. If performing jobs in this fashion, it is recommended that you use the ObjectMeta generateName feature to avoid name conflicts when jobs are run multiple times, particularly for onchange events.

An example directory structure might look something like

.
├── Dockerfile
├── README.md
├── controller.sh
├── functions.sh
├── lib
├── mycustomresource
│   ├── manifest.jsonnet
│   ├── onchange
│   ├── oncreate
│   │   └── create-job.jsonnet
│   └── ondelete
└── watches.json

If you are using Docker, you can use the bmwest/k8s-jsonnet-controller image as a base with

FROM bmwest/k8s-jsonnet-controller:latest

COPY watches.yaml .
COPY mycustomresource ./mycustomresource

This project is a work in progress. If you encounter any issues, please report them on GitHub.