ytt.md

ytt

ytt is a YAML templating tool that works on YAML structure instead of text.

It can be used to achieve complex YAML manipulation (templating, merging, patching/overlaying, modularizing, etc). Check out ytt website for an interactive playground and the documentation

ytt lovely plugin

The lovely-ytt plugin doesn't set any default configuration: in other words, using the lovely-ytt plugin is exactly the same as using the lovely plugin, except that the ytt binary is built-in.

To actually make use of ytt, you need to configure either of the plugins or preprocessors parameter (which are described here).

For example, to use it as a preprocessor, you need to configure your application as follows:

project: default
source:
  plugin:
    name: lovely-ytt
    env:
      - name: your_env_var_name
        value: eureka
    parameters:
      - name: lovely_preprocessors
        string: ytt --data-values-env=ARGOCD_ENV --file . --output-files .

The above would run ytt on a sub-application folder, and the environment variables that you specify in spec.source.plugin.env will be available for templating inside your manifest. For completeness, here is what your manifest could typically look like:

#@ load("@ytt:data", "data")
#@yaml/text-templated-strings
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: test-ytt
spec:
  selector:
    matchLabels:
      app: test-ytt
  template:
    metadata:
      labels:
        app: test-ytt
    spec:
      containers:
      - name: test-pod-(@= data.values.your_env_var_name @)
        image: docker.io/nicolaka/netshoot
        command: ["sleep"]
        args: ["infinity"]

Finally, it's worth noting that if you want to use ytt to template a Helm Chart, it's probably best to adapt the preprocessor parameter a bit, as you ytt doesn't like Helm Charts Jinja2 templates. Therefore, it's probably a good idea to only template the values.yaml file when working with Helm Charts, and to that end, you should configure the plugin with:

source:
  plugin:
    parameters:
      - name: lovely_preprocessors
        string: ytt --data-values-env=ARGOCD_ENV --file values.yaml --output-files .

Notes

ytt could also be used as a plugin rather than as a preprocessor as described above; to that end, do not set the --output-files . argument when configuring the plugin, so that ytt actually writes the rendered manifest to stdout.

Concretely, the config would be:

source:
  plugin:
    parameters:
      - name: lovely_plugins
        string: ytt --data-values-env=ARGOCD_ENV --file .