kexpand is a tool for expanding Kubernetes placeholder variables into their actual values. It implements the upcoming kubernetes templating specification client-side (with some extensions based on real-world requirements).

You can use templates today, and when k8s implements it on the server, you should hopefully not have to rewrite your manifests.

quoted form: $(key) => "value"

unquoted form: $((key)) => value

kexpand turns this:

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: $((name))
spec:
  replicas: $((replicas))
  template:
    metadata:
      labels:
        app: $((name))
    spec:
      containers:
      - name: $((name))
        image: tutum/hello-world
        ports:
        - containerPort: 80

Into this:

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: hello-world
spec:
  replicas: 3
  template:
    metadata:
      labels:
        app: hello-world
    spec:
      containers:
      - name: hello-world
        image: tutum/hello-world
        ports:
        - containerPort: 80

Build the code (make sure you have set GOPATH):

go get -d github.com/kopeio/kexpand
cd ${GOPATH}/src/github.com/kopeio/kexpand
make

The expand command will output the result of replacing all variables in the template file with the values from the provided values file:

kexpand expand deployment.yaml -f values.yaml

deployment.yaml:

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: $((name))
spec:
  replicas: $((replicas))
  template:
    metadata:
      labels:
        app: $((name))
    spec:
      containers:
      - name: $((name))
        image: tutum/hello-world
        ports:
        - containerPort: 80

values.yaml:

name: hello-world
replicas: 3

The result of expanding the template will be output to stdout, where it can be redirected to a file or piped to kubectl:

kexpand expand deployment.yaml -f values.yaml | kubectl create -f -

kexpand supports two different forms of variables: $((key)) will output a non-quoted value ($((replicas)) => 3), while $(key) will output a quoted value ($(replicas) => "3"). A legacy format, {{key}}, is also supported, but not recommended for use.

Variables names can include any alphanumeric character along with hypens(-), period(.), and underscores(_).

kexpand supprts passing multiple files and wildcards for templates to specify multiple files at once. kexpand will add --- between each filename as required by kubectl.

kexpand *.tmpl.yaml -f values.yaml

Base64 encoding of values is supported by adding |base64 to the key as in $(key|base64), $((key|base64)), and {{keyi|base64}}. This is useful for secret definitions.