Tekton Pipeline

External

• https://tekton.dev/docs/pipelines/pipelines/
• https://github.com/tektoncd/pipeline/blob/main/docs/README.md
• https://github.com/tektoncd/pipeline/blob/main/docs/pipelines.md

Internal

• Tekton Concepts
• Tekton Task

Overview

A pipeline defines a series of ordered tasks. Just like steps, a task in a pipeline can use as input the output of a previously executed task. Tekton collects all the tasks, and based on the dependency relationships declared in definition of the pipeline, it orders the tasks in a DAG, and executes the graph in sequence. That results in the materialization of a number of task pods. The pipeline comes up with additional features, such as the capability to fan-out task execution, retry task execution or verify conditions that tasks must meet before proceeding. The pipeline is implemented as a Kubernetes custom resource.

Example

apiVersion: tekton.dev/v1beta1
kind: Task
metadata:
  name: task1
spec:
  steps:
    - name: echo
      image: alpine
      script: |
        #!/bin/sh
        echo "this is Task 1 output"
---
apiVersion: tekton.dev/v1beta1
kind: Task
metadata:
  name: task2
spec:
  steps:
    - name: echo
      image: alpine
      script: |
        #!/bin/sh
        echo "this is Task 2 output"
---
apiVersion: tekton.dev/v1beta1
kind: Pipeline
metadata:
  name: simple-pipeline
spec:
  tasks:
    - name: task1
      taskRef:
        name: task1
    - name: task2
      runAfter:
        - task1
      taskRef:
        name: task2

Manifest

apiVersion: tekton.dev/v1beta1 # required field
kind: Pipeline                 # required field
metadata:                      # required field
  name: <pipeline-name>        # required field
spec:                          # required field
  workspaces:
    - name: <workspace-name>
  params:
    - name: <some-string-param-name>
      type: string
      description: some description
      default: <some-default-value>
    - name: <some-array-param-name>
      type: array
      description:  some description
  resources:
  tasks:                       # required field
    - name: task1-name
      taskRef:
        name: task1-ref-name 
    - name: task2-name
      taskRef:
        name: task2-ref-name 
    - ...

Tasks in Pipeline

The pipeline specification contains a mandatory list of tasks. The list specifies the tasks of this pipeline and the details of their execution. The pipeline definition must reference at least one task. Each task must be specified via a valid Kubernetes name and a taskRef.

kind: Pipeline
spec:
  tasks:
    - name: task-name
      taskRef:
        name: task-ref-name 
        bundle: docker.com/myrepo/mycatalog
      retries: 3
      runAfter:
        - some-task-name
        - some-other-task-name
      params:
        - name: param-name 
          value: param-value 
      matrix:
        - name: matrix-name 
          value:
            - value1 
            - value2 
      workspaces:
        - name: <name>
          workspace: <workspace>
      resources:
        inputs:
          - name: input-resource-name 
             resource: input-resource 
        outputs:
          - name: output-resource-name 
             resource: output-resource 

Execution Order

To clarify. Is the order in which the tasks have been declared?

runAfter

https://tekton.dev/docs/pipelines/pipelines/#using-the-runafter-field

Use runAfter field to indicate that the task it shows up on must run after the tasks declared in the runAfter list. This order is enforced regardless of the order in which the tasks are specified in the pipeline definition.

Retries

A task execution can be retired a number of times if the if fails. The number of retires is specified using the retries field in the task declaration in the pipeline.

https://tekton.dev/docs/pipelines/pipelines/#using-the-retries-field

Conditional Execution with when

TO PROCESS:

• https://tekton.dev/docs/pipelines/pipelines/#guard-task-execution-using-when-expressions
• https://tekton.dev/docs/pipelines/pipelines/#guarding-a-task-and-its-dependent-tasks

Resources

TO PROCESS: https://tekton.dev/docs/pipelines/pipelines/#specifying-resources-in-pipelinetasks