helm-style-values.md

Kubernetes & Helm-style values

Consider the following example of creating a Kubernetes secret for a tls.crt file -- in real environments, you'll also need the key, but for the sake of this example, it has been omitted.

Checking the files in the folder:

tree .

.
├── secret.yaml
└── tls.crt

0 directories, 2 files

We have a secret.yaml which includes tgen templating notation:

cat secret.yaml

apiVersion: v1
kind: Secret
metadata:
  name: secret-tls
type: kubernetes.io/tls
data:
  tls.crt: | {{ readfile "tls.crt" | b64enc | nindent 4 }}

The last line includes the following logic:

• Reads the tls.crt file from the current directory where tgen is run
• Takes the contents of the file and converts it to base64 -- required by Kubernetes secrets
• Then indents with 4 spaces, starting with a new line

To generate the output, we can now run tgen:

tgen -f secret.yaml

And the output looks like this:

apiVersion: v1
kind: Secret
metadata:
  name: secret-tls
type: kubernetes.io/tls
data:
  tls.crt: |
    Rk9PQkFSQkFaCg==

This output can be then passed to Kubernetes as follows:

tgen -f secret.yaml | kubectl apply -f -

Do keep in mind though your DevOps requirements in terms of keeping a copy of your YAML files, rendered. Additionally, the readfile function is akin to helm's .Files, with the exception that you can read any file the tgen binary has access, including potentially sensitive files such as /etc/passwd. If this is a concern, please run tgen in a CI/CD environment or where access to these resources is limited.

You can also use a values.yaml file like Helm. tgen will allow you to read values from the values file as .variable or .Values.variable. The latter is the same as Helm's .Values.variable and the former is a shortcut to .Values.variable for convenience. Consider the following YAML values file:

name: Patrick

And the following template:

Hello, my name is {{ .name }}.

Running tgen with the values file will yield the following output:

$ tgen -f template.yaml -v values.yaml
Hello, my name is Patrick.

If your values file is called values.yaml, you also have the handy shortcut of simply specifying --with-values and tgen will automatically include the values file from the current working directory.