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Templating a Single Pipeline

The smallest ytt setup: one template file describing the shape of a pipeline, and one data values file supplying the parts that change. Render them together, and you get a plain pipeline YAML file, ready for fly set-pipeline.

The Files

template.yml — the pipeline's shape, with #@ markers where values get substituted in:

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#@ load("@ytt:data", "data")
jobs:
- name: #@ data.values.job_name + "-job"
  plan:
  - task: #@ data.values.task_name
    config:
      platform: linux
      image_resource:
        type: mock
        source:
          mirror_self: true
      run:
        path: echo
        args: #@ data.values.args

vars.yml — the data values referenced above, marked with #@data/values so ytt knows to load them as inputs rather than treat them as a second template:

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#@data/values
---
job_name: "hello-world"
task_name: "hello-task"
args:
  - "hello world of vars!"

Rendering

With both files in the same directory, either of these produce the same output:

# explicit files
ytt -f template.yml -f vars.yml > rendered.yml

# everything in the current directory
ytt -f . > rendered.yml

This is what gets rendered:

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jobs:
  - name: hello-world-job
    plan:
      - task: hello-task
        config:
          platform: linux
          image_resource:
            type: mock
            source:
              mirror_self: true
          run:
            path: echo
            args:
              - "hello world of vars!"

Setting the Pipeline

Treat rendered.yml like any other pipeline file:

fly -t main set-pipeline -p hello-world -c rendered.yml

Or, to render and set it in one motion from inside a pipeline, do the rendering in a task and feed the output straight into a set_pipeline step:

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jobs:
  - name: set-single-rendered
    plan:
      - task: render-pipeline
        config:
          platform: linux
          image_resource:
            type: mock
            source:
              mirror_self: true
          inputs:
            - name: repo
          outputs:
            - name: pipeline
          run:
            path: sh
            args:
              - -c
              - |
                apk add --no-progress --quiet ytt
                ytt -f repo/template.yml -f repo/vars.yml > pipeline/rendered.yml

      - set_pipeline: hello-world
        file: pipeline/rendered.yml