Task With Parameters

One of the goals that you should aim for when building your tasks is to make them reusable as much as possible. A simple way to reuse a task in different contexts is to add parameters to them. You can then substitute the values of those parameters in the steps that compose your task.

String Parameter

Create a new task with more reusable

The goal is now to make this task reusable in different contexts. Instead of always outputting Hello World, we now want it to say hello to anyone.

you can create a new file called name-param.yaml with below contents.

apiVersion: tekton.dev/v1beta1
kind: Task
metadata:
  name: name-param
spec:
  params:
    - name: name
      type: string
  steps:
    - image: ubuntu
      command:
        - /bin/bash
        - -c
        - echo "Hello $(params.name)"

Parameters are added in the spec section of the task. This new params field will contain a list of parameters. For each parameter, you will add a name and a type. The type can be either string or array.

now we can use $(params.<NAME_OF_PARAMETER>). It will be replaced with the value of the given parameter.

Now we are ready to run your first parametrized task. Start this new task just as you would with any other normal task:

let's apply this task in our Kubernetes cluster using the below command

learning-ocean:~ gaurav$ kubectl apply -f 04-name-param.yaml 
task.tekton.dev/name-param created
learning-ocean:~ gaurav$ 

let's start the task using the below command

learning-ocean:~ gaurav$ tkn task start name-param --showlog
? Value for param `name` of type `string`? Learning-Ocean
TaskRun started: name-param-run-2d65g
Waiting for logs to be available...
[unnamed-0] Hello Learning-Ocean
learning-ocean:~ gaurav$ 

This time, we should be prompted by the tkn CLI tool to add a value for the name parameter. we can also pass in the values for the parameters directly in the command line by using the -p argument:

learning-ocean:~ gaurav$ tkn task start name-param --showlog -p name=Learning-Ocean
TaskRun started: name-param-run-g5s5b
Waiting for logs to be available...
[unnamed-0] Hello Learning-Ocean
learning-ocean:~ gaurav$ 

The result will be the same, but Tekton won't prompt you for the parameter value.

Array Parameters

We can also use parameters of type array. These parameters will contain an array of values that can then be expanded anywhere an array is used. This type of parameter can be convenient when you expect an unknown number of arguments to a command or a script that you might want to run.

In this next example, we will create a task that can take any number of student's items and then list them in the form of students list.

apiVersion: tekton.dev/v1beta1
kind: Task
metadata:
  name: array-params
spec:
  params:
    - name: students
      type: array
  steps:
    - name: printstudents
      image: ubuntu
      args:
        - $(params.students[*])
      script: |
        #!/bin/bash
        for i in $@
        do
          echo $i
        done

When you run this task, you will be asked to enter a value for items. You can type in a list of comma-separated values.

learning-ocean:~ gaurav$ kubectl apply -f array-param.yaml 
task.tekton.dev/array-params created

start the task below command

learning-ocean:~ gaurav$ tkn task start array-params --showlog
? Value for param `students` of type `array`? gaurav,saurav,manish
TaskRun started: array-params-run-xkckn
Waiting for logs to be available...
[printstudents] gaurav
[printstudents] saurav
[printstudents] manish
learning-ocean:~ gaurav$ 

Adding a default value

We can also add a default value to our parameters. You can do this by adding a default field to the param object.

let's see with example create a new file default-value-param.yaml with below content.

apiVersion: tekton.dev/v1beta1
kind: Task
metadata:
  name: default-param
spec:
  params:
    - name: name
      type: string
      default: gaurav
  steps:
    - name: hello world
      image: ubuntu
      command:
        - /bin/bash
        - -c
        - echo "Hello $(params.name)"

apply this new file to Kubernetes cluster using below command:

learning-ocean:~ gaurav$ kubectl apply -f design/default-param.yaml 
task.tekton.dev/default-param created
learning-ocean:~ gaurav$ 

now, start this task, you will see the default value proposed by the tkn CLI tool. Hit Enter to accept the default value suggested:

learning-ocean:~ gaurav$ tkn task start default-param --showlog
? Value for param `name` of type `string`? (Default is `gaurav`) gaurav
TaskRun started: default-param-run-mpns7
Waiting for logs to be available...
[hellouser] Hello gaurav
learning-ocean:~ gaurav$ 

You can also use --use-param-defaults to start this task run immediately with the default values for those parameters:

learning-ocean:~ gaurav$ tkn task start default-param --showlog --use-param-defaults
TaskRun started: default-param-run-chv28
Waiting for logs to be available...
[hellouser] Hello gaurav
learning-ocean:~ gaurav$ 

Task parameters can be used in one or many steps if you need to. That can be useful to share inputs for your steps.