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Pluggable generator for creating, using and sharing reusable templates that can be applied directly, generated into operator, helm chart and more!

by observatorium

v0.0.0-20210510211024-fdcbe3da7485 (see all)License:Apache-2.0
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rndr (render): Simplify your cloud native system adoption with rndr templates!

Work in heavy progress (exeprimental phase): API and implementation might change.

rndr provides a pluggable generator for creating, using and sharing reusable templates that can be expanded into deployment manifests for systems like Kubernetes and beyond, generated into operator or helm! rndr can be more or less compared to helm - but on steroids (see the comparison below).

TODO(bwplotka): If prototype is generally approved, move this to separate org (kind of created


  • Abstract away classic boilerplate or show example deployment model of your system in an easy, reproducible way you can use on production.
  • Use templating engine of your choice without exposing this detail to the user! Anything that "runs" as definitive OS process is supported

Trust us: Most likely user don't want to see raw jsonnet (:

  • Maintain stable and easy to use template values in either go or proto allowing easy validation of template values on render time.
  • Tight integration with charts. Generate helm charts from your system's rndr template or use chart as rndr template itself.
  • You can't escape from #operator movement. rndr allows to render your deployment state for both GitOps use and operator use. With simple operator option instead of raw resources rndr will generate you a ready to use operator allowing to reconcile state in runtime.
  • Currently supports Kubernetes only, but can be extended for other orchestator systems using declarative configuration.


  • Deploying is explicitly a domain of other tools like kube apply, locutus, helm and others.


Creating template for your system deployment

Let's define some example template that allows easy deploy of example helloservice.

  1. Create a template in the templating language you love! It can be helm chart, jsonnet, cue, Go templates or even golang or python! Anything that will take template input in YAML and produce resources in YAML files that declare the desired state of the system.

  2. Define API for values (values definition) in go or proto. Make sure your templating engine consumes YAML and JSON marshalled by such definition.

NOTE: See example here. There are tons of good practices for maintaining stable and easy to consume API definition (backward compatibility, 'extra' fields etc). Refer to for details.

  1. Tell rndr where values definition are (api field) and where and how to use your templating language (renderer).

For example, you could have hellosvc.tmpl.yaml (as you can see how it's used defined in our example directory)

version: v1
name: "helloservice"
authors: ""

  # api defines the definition of values.
      default: ""
      struct: ""
  #  or
  #  proto:
  #    entry: "Config"
  #    message: "openproto/protoconfig.proto"
  # renderer defines the rendering engine.
      # functions represent a local or absolute paths to .jsonnet files with
      # single `function(values) {` that renders manifests in right order.
      # Each function's manifests will be part of different groups allowing parallel rollout if requested.
      functions: [hellosvc.libsonnet]
  #  or
  #  helm:
  #    chart: prometheus
  #    repo: 
  #  or
  #  process:
  #    command: "./my-cmd"
  #    inputEnvVar: "INPUT"
  #    arguments:
  #    - "--config=${INPUT}

    outputDir: ./olm
    outputDir: ./operator
    outputDir: ./helm
    outputDir: ./oc

Using your template to render desired deployment state

With the template and value definitions we can use rndr to render Kubernetes resources with values we want that are ready to be deployed by your own GitOps pipeline or just using kube apply!

rndr -t="hellosvc.tmpl.yaml" kubernetes manifests --values="my-special-hellosvc.values.yaml" -o "./here" 

Run and see examples:

Using rndr to generate operator!

This command will generate Kubernetes resources that use locutus project for reconciling your resources from inside the cluster.

rndr -t="hellosvc.tmpl.yaml" kubernetes operator -o "./here" 

Using rndr to generate helm chart from your template (!)

There is always the same question for all of the project maintainers. Everyone wants to use helm charts, no one want to maintain them. What if you can use your favorite templating tool to generate ... helm chart?

It's as easy as single command:

rndr -t="hellosvc.tmpl.yaml" kubernetes helm -o "./here" 

Make it easy to support helm chart users even if you don't use helm yourself!

Using rndr to generate... jsonnet?

So maybe your company loves jsonnet, but you don't. We hear you! With rndr you can use your own language and generate jsonnet package. It's as simple as:

rndr -t="hellosvc.tmpl.yaml" --values="my-special-hellosvc.yaml" kubernetes jsonnet -o "./here" 


  • helm:

    • helm tries to solve both templating and deployment. rndr believes in do one thing and do it well UNIX philosophy and focuses on templating part only.
    • rndr allows to render resources or operator that will operate those resources (thanks to locutus project)
    • rndr aims to have stable, backward and forward compatible API for your templates (using protobuf). That's hard with helm charts.
    • rndr allows to use more advanced templating then just Go Templating.
  • Helm charts as operator:


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