Questions tagged [ytt]

ytt - YAML Templating Tool

Given a set of YAML files, you want to:

• inject variables, conditionally include parts, or loop over a list and generate chunks of YAML; and/or
• apply a set of edits (like a patch) that are guaranteed to result in valid YAML.

and, you want it to be:

• maintainable — even when templated, YAML files are human-readable
• deterministic — given the same inputs, get the same output
• scalable — as you wrangle more YAML, you can keep it sensibly organized
• general-purpose — manage all your YAML (Kubernetes manifests, Docker Compose, Concourse Pipeline, Envoy config, Travis build config, etc.) with one tool

ytt does that:

• templates are written using intuitive Python-like syntax
• extract whole chunks of YAML into functions that can be invoked without thinking about escaping or indentation
• group things into libraries to be reused and shared
• ensures execution is deterministic by giving no access to the filesystem, network, time, randomness, or operating system interfaces

ytt is part of the Carvel suite (pronounced /ˈkɑr vəl/; rhymes with "marvel"), an Open Source project containing a set of small sharp tools that support packaging and deploying software on Kubernetes.

Example

(See this example and others in the online ytt Playground)

Given a ytt template:

config.yml

#@ load("@ytt:data", "data")

#@ def/end labels():
app: apple

kind: Pod
apiVersion: v1
metadata:
  name: apple-app
  labels: #@ labels()
spec:
  containers:
  - name: apple-app
    image: hashicorp/http-echo
    args:
    - #@ "-listen=:" + str(data.values.port)
    - #@ "-text=" + data.values.text
---
kind: Service
apiVersion: v1
metadata:
  name: apple-service
spec:
  selector: #@ labels()
  ports:
  - port: #@ data.values.port

... and a set of values ...

values.yml

#@data/values
---
port: 8080
#! note how text is quoted automatically in the result file
text: "Hello #ytt World!"

Running ytt...

$ ytt -f config.yml -f values.yml

...yields...

kind: Pod
apiVersion: v1
metadata:
  name: apple-app
  labels:
    app: apple
spec:
  containers:
  - name: apple-app
    image: hashicorp/http-echo
    args:
    - -listen=:8080
    - '-text=Hello #ytt World!'
---
kind: Service
apiVersion: v1
metadata:
  name: apple-service
spec:
  selector:
    app: apple
  ports:
  - port: 8080