Manifestor

Small utility to interpolate environment variables into Kubernetes manifests. Unlike many other templating mechanisms, this utility will never output an invalid YAML.

Under the hood, it parses the input yaml files, finds string values, interpolates environment values into them using bash-like interpolation syntax and then re-assembles the resulting YAML(s) that are printed on stdout.

Also, there is an option of executing pre and post interpolation processors in ECMAScript 5.1(+).

Use

$ VAR=VALUE manifestor [--processors=] [<yaml file> ...] | kubectl apply -f -

Interpolation format

We are using envsubst to interpolate environment variables into the string values.

TL;DR;

running

HOSTNAME="localhost" manifestor ingress.yaml

where ingress.yaml template looks like this:

apiVersion: extensions/v1beta1
kind: Ingress
metadata:
    annotations:
        kubernetes.io/ingress.class: nginx
    name: api
    namespace: api
spec:
    rules:
        - host: ${HOSTNAME}
          http:
            paths:
                - backend:
                    serviceName: api
                    servicePort: 3030
                  path: /api

will result in the following output:

apiVersion: extensions/v1beta1
kind: Ingress
metadata:
    annotations:
        kubernetes.io/ingress.class: nginx
    name: api
    namespace: api
spec:
    rules:
        - host: localhost
          http:
            paths:
                - backend:
                    serviceName: api
                    servicePort: 3030
                  path: /api

Pre and post interpolation processors

String interpolation of environment variables is quite limited. It won't cater for the cases where a number, boolean value or a whole sub-object needs to be changed, inserted or deleted. In order to cover those cases, we support executing so-called processors.

A processor is a JavaScript function that takes an object representing one entity from the manifest and can change it in place.

Interpolating JS objects directly in yaml

If a more complex object has to be interpolated, any string value starting with $$JS: will get evaluated and the result of the evaluation will replace the original string.

e.g.

abc: '$$JS: env.GREEN_EGGS_ONLY ? "green eggs" : ["green eggs", "ham"]'

will evaluate to:

abc: green eggs

if environment variable GREEN_EGGS_ONLY is not set or it has an empty value.

In any other case, the result of the evaluation will be:

abc:
    - green eggs
    - ham

Naming convention

TODO

Available functions

TODO

Available objects

env

env contains environment variables passed to the process as key/value object