Tasks

Overview

A Task is a collection of Steps that you define and arrange in a specific order of execution as part of your continuous integration flow. A Task executes as a Pod on your Kubernetes cluster. A Task is available within a specific namespace, while a ClusterTask is available across the entire cluster.

A Task declaration includes the following elements:

Configuring a Task

A Task definition supports the following fields:

  • Required:
    • apiVersion - Specifies the API version. For example, tekton.dev/v1beta1.
    • kind - Identifies this resource object as a Task object.
    • metadata - Specifies metadata that uniquely identifies the Task resource object. For example, a name.
    • spec - Specifies the configuration information for this Task resource object.
    • steps - Specifies one or more container images to run in the Task.
  • Optional:
    • description - An informative description of the Task.
    • params - Specifies execution parameters for the Task.
    • workspaces - Specifies paths to volumes required by the Task.
    • results - Specifies the names under which Tasks write execution results.
    • volumes - Specifies one or more volumes that will be available to the Steps in the Task.
    • stepTemplate - Specifies a Container step definition to use as the basis for all Steps in the Task.
    • sidecars - Specifies Sidecar containers to run alongside the Steps in the Task.

The non-functional example below demonstrates the use of most of the above-mentioned fields:

apiVersion: tekton.dev/v1 # or tekton.dev/v1beta1
kind: Task
metadata:
  name: example-task-name
spec:
  params:
    - name: pathToDockerFile
      type: string
      description: The path to the dockerfile to build
      default: /workspace/workspace/Dockerfile
    - name: builtImageUrl
      type: string
      description: location to push the built image to
  steps:
    - name: ubuntu-example
      image: ubuntu
      args: ["ubuntu-build-example", "SECRETS-example.md"]
    - image: gcr.io/example-builders/build-example
      command: ["echo"]
      args: ["$(params.pathToDockerFile)"]
    - name: dockerfile-pushexample
      image: gcr.io/example-builders/push-example
      args: ["push", "$(params.builtImageUrl)"]
      volumeMounts:
        - name: docker-socket-example
          mountPath: /var/run/docker.sock
  volumes:
    - name: example-volume
      emptyDir: {}

Task vs. ClusterTask

Note: ClusterTasks are deprecated. Please use the cluster resolver instead.

A ClusterTask is a Task scoped to the entire cluster instead of a single namespace. A ClusterTask behaves identically to a Task and therefore everything in this document applies to both.

Note: When using a ClusterTask, you must explicitly set the kind sub-field in the taskRef field to ClusterTask. If not specified, the kind sub-field defaults to Task.

Below is an example of a Pipeline declaration that uses a ClusterTask: Note:

  • There is no v1 API specification for ClusterTask but a v1beta1 clustertask can still be referenced in a v1 pipeline.
  • The cluster resolver syntax below can be used to reference any task, not just a clustertask.
apiVersion: tekton.dev/v1
kind: Pipeline
metadata:
  name: demo-pipeline
spec:
  tasks:
    - name: build-skaffold-web
      taskRef:
        resolver: cluster
        params:
        - name: kind
          value: task
        - name: name
          value: build-push
        - name: namespace
          value: default

apiVersion: tekton.dev/v1beta1
kind: Pipeline
metadata:
  name: demo-pipeline
  namespace: default
spec:
  tasks:
    - name: build-skaffold-web
      taskRef:
        name: build-push
        kind: ClusterTask
      params: ....

Defining Steps

A Step is a reference to a container image that executes a specific tool on a specific input and produces a specific output. To add Steps to a Task you define a steps field (required) containing a list of desired Steps. The order in which the Steps appear in this list is the order in which they will execute.

The following requirements apply to each container image referenced in a steps field:

  • The container image must abide by the container contract.
  • Each container image runs to completion or until the first failure occurs.
  • The CPU, memory, and ephemeral storage resource requests set on Steps will be adjusted to comply with any LimitRanges present in the Namespace. In addition, Kubernetes determines a pod’s effective resource requests and limits by summing the requests and limits for all its containers, even though Tekton runs Steps sequentially. For more detail, see Compute Resources in Tekton.

Note: If the image referenced in the step field is from a private registry, TaskRuns or PipelineRuns that consume the task must provide the imagePullSecrets in a podTemplate.

Below is an example of setting the resource requests and limits for a step:

spec:
  steps:
    - name: step-with-limts
      computeResources:
        requests:
          memory: 1Gi
          cpu: 500m
        limits:
          memory: 2Gi
          cpu: 800m

spec:
  steps:
    - name: step-with-limts
      resources:
        requests:
          memory: 1Gi
          cpu: 500m
        limits:
          memory: 2Gi
          cpu: 800m

Reserved directories

There are several directories that all Tasks run by Tekton will treat as special

Running scripts within Steps

A step can specify a script field, which contains the body of a script. That script is invoked as if it were stored inside the container image, and any args are passed directly to it.

Note: If the script field is present, the step cannot also contain a command field.

Scripts that do not start with a shebang line will have the following default preamble prepended:

#!/bin/sh
set -e

You can override this default preamble by prepending a shebang that specifies the desired parser. This parser must be present within that Step's container image.

The example below executes a Bash script:

steps:
  - image: ubuntu # contains bash
    script: |
      #!/usr/bin/env bash
      echo "Hello from Bash!"

The example below executes a Python script:

steps:
  - image: python # contains python
    script: |
      #!/usr/bin/env python3
      print("Hello from Python!")

The example below executes a Node script:

steps:
  - image: node # contains node
    script: |
      #!/usr/bin/env node
      console.log("Hello from Node!")

You can execute scripts directly in the workspace:

steps:
  - image: ubuntu
    script: |
      #!/usr/bin/env bash
      /workspace/my-script.sh  # provided by an input resource

You can also execute scripts within the container image:

steps:
  - image: my-image # contains /bin/my-binary
    script: |
      #!/usr/bin/env bash
      /bin/my-binary
Windows scripts

Scripts in tasks that will eventually run on windows nodes need a custom shebang line, so that Tekton knows how to run the script. The format of the shebang line is:

#!win <interpreter command> <args>

Unlike linux, we need to specify how to interpret the script file which is generated by Tekton. The example below shows how to execute a powershell script:

steps:
  - image: mcr.microsoft.com/windows/servercore:1809
    script: |
      #!win powershell.exe -File
      echo 'Hello from PowerShell'

Microsoft provide powershell images, which contain Powershell Core (which is slightly different from powershell found in standard windows images). The example below shows how to use these images:

steps:
  - image: mcr.microsoft.com/powershell:nanoserver
    script: |
      #!win pwsh.exe -File
      echo 'Hello from PowerShell Core'

As can be seen the command is different. The windows shebang can be used for any interpreter, as long as it exists in the image and can interpret commands from a file. The example below executes a Python script:

  steps:
  - image: python
    script: |
      #!win python
      print("Hello from Python!")

Note that other than the #!win shebang the example is identical to the earlier linux example.

Finally, if no interpreter is specified on the #!win line then the script will be treated as a windows .cmd file which will be excecuted. The example below shows this:

  steps:
  - image: mcr.microsoft.com/powershell:lts-nanoserver-1809
    script: |
      #!win
      echo Hello from the default cmd file

Specifying a timeout

A Step can specify a timeout field. If the Step execution time exceeds the specified timeout, the Step kills its running process and any subsequent Steps in the TaskRun will not be executed. The TaskRun is placed into a Failed condition. An accompanying log describing which Step timed out is written as the Failed condition’s message.

The timeout specification follows the duration format as specified in the Go time package (e.g. 1s or 1ms).

The example Step below is supposed to sleep for 60 seconds but will be canceled by the specified 5 second timeout.

steps:
  - name: sleep-then-timeout
    image: ubuntu
    script: |
      #!/usr/bin/env bash
      echo "I am supposed to sleep for 60 seconds!"
      sleep 60      
    timeout: 5s

Specifying onError for a step

When a step in a task results in a failure, the rest of the steps in the task are skipped and the taskRun is declared a failure. If you would like to ignore such step errors and continue executing the rest of the steps in the task, you can specify onError for such a step.

onError can be set to either continue or stopAndFail as part of the step definition. If onError is set to continue, the entrypoint sets the original failed exit code of the script in the container terminated state. A step with onError set to continue does not fail the taskRun and continues executing the rest of the steps in a task.

To ignore a step error, set onError to continue:

steps:
  - image: docker.io/library/golang:latest
    name: ignore-unit-test-failure
    onError: continue
    script: |
            go test .

The original failed exit code of the script is available in the terminated state of the container.

kubectl get tr taskrun-unit-test-t6qcl -o json | jq .status
{
  "conditions": [
    {
      "message": "All Steps have completed executing",
      "reason": "Succeeded",
      "status": "True",
      "type": "Succeeded"
    }
  ],
  "steps": [
    {
      "container": "step-ignore-unit-test-failure",
      "imageID": "...",
      "name": "ignore-unit-test-failure",
      "terminated": {
        "containerID": "...",
        "exitCode": 1,
        "reason": "Completed",
      }
    },
  ],

For an end-to-end example, see the taskRun ignoring a step error and the pipelineRun ignoring a step error.

Accessing Step’s exitCode in subsequent Steps

A step can access the exit code of any previous step by reading the file pointed to by the exitCode path variable:

cat $(steps.step-<step-name>.exitCode.path)

The exitCode of a step without any name can be referenced using:

cat $(steps.step-unnamed-<step-index>.exitCode.path)

Produce a task result with onError

When a step is set to ignore the step error and if that step is able to initialize a result file before failing, that result is made available to its consumer task.

steps:
  - name: ignore-failure-and-produce-a-result
    onError: continue
    image: busybox
    script: |
      echo -n 123 | tee $(results.result1.path)
      exit 1

The task consuming the result using the result reference $(tasks.task1.results.result1) in a pipeline will be able to access the result and run with the resolved value.

Now, a step can fail before initializing a result and the pipeline can ignore such step failure. But, the pipeline will fail with InvalidTaskResultReference if it has a task consuming that task result. For example, any task consuming $(tasks.task1.results.result2) will cause the pipeline to fail.

steps:
  - name: ignore-failure-and-produce-a-result
    onError: continue
    image: busybox
    script: |
      echo -n 123 | tee $(results.result1.path)
      exit 1
      echo -n 456 | tee $(results.result2.path)

Breakpoint on failure with onError

Debugging a taskRun is supported to debug a container and comes with a set of tools to declare the step as a failure or a success. Specifying breakpoint at the taskRun level overrides ignoring a step error using onError.

Redirecting step output streams with stdoutConfig and stderrConfig

This is an alpha feature. The enable-api-fields feature flag must be set to "alpha" for Redirecting Step Output Streams to function.

This feature defines optional Step fields stdoutConfig and stderrConfig which can be used to redirection the output streams stdout and stderr respectively:

- name: ...
  ...
  stdoutConfig:
    path: ...
  stderrConfig:
    path: ...

Once stdoutConfig.path or stderrConfig.path is specified, the corresponding output stream will be duplicated to both the given file and the standard output stream of the container, so users can still view the output through the Pod log API. If both stdoutConfig.path and stderrConfig.path are set to the same value, outputs from both streams will be interleaved in the same file, but there will be no ordering guarantee on the data. If multiple Step’s stdoutConfig.path fields are set to the same value, the file content will be overwritten by the last outputting step.

Variable substitution will be applied to the new fields, so one could specify $(results.<name>.path) to the stdoutConfig.path or stderrConfig.path field to extract the stdout of a step into a Task result.

Example Usage

Redirecting stdout of boskosctl to jq and publish the resulting project-id as a Task result:

apiVersion: tekton.dev/v1 # or tekton.dev/v1beta1
kind: Task
metadata:
  name: boskos-acquire
spec:
  results:
  - name: project-id
  steps:
  - name: boskosctl
    image: gcr.io/k8s-staging-boskos/boskosctl
    args:
    - acquire
    - --server-url=http://boskos.test-pods.svc.cluster.local
    - --owner-name=christie-test-boskos
    - --type=gke-project
    - --state=free
    - --target-state=busy
    stdoutConfig:
      path: /data/boskosctl-stdout
    volumeMounts:
    - name: data
      mountPath: /data
  - name: parse-project-id
    image: imega/jq
    args:
    - -r
    - .name
    - /data/boskosctl-stdout
    stdoutConfig:
      path: $(results.project-id.path)
    volumeMounts:
    - name: data
      mountPath: /data
  volumes:
  - name: data

NOTE:

  • If the intent is to share output between Steps via a file, the user must ensure that the paths provided are shared between the Steps (e.g via volumes).
  • There is currently a limit on the overall size of the Task results. If the stdout/stderr of a step is set to the path of a Task result and the step prints too many data, the result manifest would become too large. Currently the entrypoint binary will fail if that happens.
  • If the stdout/stderr of a Step is set to the path of a Task result, e.g. $(results.empty.path), but that result is not defined for the Task, the Step will run but the output will be captured in a file named $(results.empty.path) in the current working directory. Similarly, any stubstition that is not valid, e.g. $(some.invalid.path)/out.txt, will be left as-is and will result in a file path $(some.invalid.path)/out.txt relative to the current working directory.

Specifying Parameters

You can specify parameters, such as compilation flags or artifact names, that you want to supply to the Task at execution time. Parameters are passed to the Task from its corresponding TaskRun.

Parameter name

Parameter name format:

  • Must only contain alphanumeric characters, hyphens (-), underscores (_), and dots (.). However, object parameter name and its key names can’t contain dots (.). See the reasons in the third item added in this PR.
  • Must begin with a letter or an underscore (_).

For example, foo.Is-Bar_ is a valid parameter name for string or array type, but is invalid for object parameter because it contains dots. On the other hand, barIsBa$ or 0banana are invalid for all types.

NOTE:

  1. Parameter names are case insensitive. For example, APPLE and apple will be treated as equal. If they appear in the same TaskSpec’s params, it will be rejected as invalid.
  2. If a parameter name contains dots (.), it must be referenced by using the bracket notation with either single or double quotes i.e. $(params['foo.bar']), $(params["foo.bar"]). See the following example for more information.

Parameter type

Each declared parameter has a type field, which can be set to string, array or object.

object type

object type is useful in cases where users want to group related parameters. For example, an object parameter called gitrepo can contain both the url and the commmit to group related information:

spec:
  params:
    - name: gitrepo
      type: object
      properties:
        url:
          type: string
        commit:
          type: string

Refer to the TaskRun example and the PipelineRun example in which object parameters are demonstrated.

NOTE:

  • object param must specify the properties section to define the schema i.e. what keys are available for this object param. See how to define properties section in the following example and the TEP-0075.
  • When providing value for an object param, one may provide values for just a subset of keys in spec’s default, and provide values for the rest of keys at runtime (example).
  • When using object in variable replacement, users can only access its individual key (“child” member) of the object by its name i.e. $(params.gitrepo.url). Using an entire object as a value is only allowed when the value is also an object like this example. See more details about using object param from the TEP-0075.
array type

array type is useful in cases where the number of compilation flags being supplied to a task varies throughout the Task's execution. array param can be defined by setting type to array. Also, array params only supports string array i.e. each array element has to be of type string.

spec:
  params:
    - name: flags
      type: array
string type

If not specified, the type field defaults to string. When the actual parameter value is supplied, its parsed type is validated against the type field.

The following example illustrates the use of Parameters in a Task. The Task declares 3 input parameters named gitrepo (of type object), flags (of type array) and someURL (of type string). These parameters are used in the steps.args list

  • For object parameter, you can only use individual members (aka keys).
  • You can expand parameters of type array inside an existing array using the star operator. In this example, flags contains the star operator: $(params.flags[*]).

Note: Input parameter values can be used as variables throughout the Task by using variable substitution.

apiVersion: tekton.dev/v1 # or tekton.dev/v1beta1
kind: Task
metadata:
  name: task-with-parameters
spec:
  params:
    - name: gitrepo
      type: object
      properties:
        url:
          type: string
        commit:
          type: string
    - name: flags
      type: array
    - name: someURL
      type: string
    - name: foo.bar
      description: "the name contains dot character"
      default: "test"
  steps:
    - name: do-the-clone
      image: some-git-image
      args: [
        "-url=$(params.gitrepo.url)",
        "-revision=$(params.gitrepo.commit)"
      ]
    - name: build
      image: my-builder
      args: [
        "build",
        "$(params.flags[*])",
        # It would be equivalent to use $(params["someURL"]) here,
        # which is necessary when the parameter name contains '.'
        # characters (e.g. `$(params["some.other.URL"])`). See the example in step "echo-param"
        'url=$(params.someURL)',
      ]
    - name: echo-param
      image: bash
      args: [
        "echo",
        "$(params['foo.bar'])",
      ]

The following TaskRun supplies the value for the parameter gitrepo, flags and someURL:

apiVersion: tekton.dev/v1 # or tekton.dev/v1beta1
kind: TaskRun
metadata:
  name: run-with-parameters
spec:
  taskRef:
    name: task-with-parameters
  params:
    - name: gitrepo
      value:
        url: "abc.com"
        commit: "c12b72"
    - name: flags
      value:
        - "--set"
        - "arg1=foo"
        - "--randomflag"
        - "--someotherflag"
    - name: someURL
      value: "http://google.com"

Default value

Parameter declarations (within Tasks and Pipelines) can include default values which will be used if the parameter is not specified, for example to specify defaults for both string params and array params (full example) :

apiVersion: tekton.dev/v1 # or tekton.dev/v1beta1
kind: Task
metadata:
  name: task-with-array-default
spec:
  params:
    - name: flags
      type: array
      default:
        - "--set"
        - "arg1=foo"
        - "--randomflag"
        - "--someotherflag"

Param enum

🌱 enum is an alpha feature. The enable-param-enum feature flag must be set to "true" to enable this feature.

Parameter declarations can include enum which is a predefine set of valid values that can be accepted by the Param. If a Param has both enum and default value, the default value must be in the enum set. For example, the valid/allowed values for Param “message” is bounded to v1, v2 and v3:

apiVersion: tekton.dev/v1
kind: Task
metadata:
  name: param-enum-demo
spec:
  params:
  - name: message
    type: string
    enum: ["v1", "v2", "v3"]
    default: "v1"
  steps:
  - name: build
    image: bash:latest
    script: |
            echo "$(params.message)"

If the Param value passed in by TaskRuns is NOT in the predefined enum list, the TaskRuns will fail with reason InvalidParamValue.

See usage in this example

Specifying Workspaces

Workspaces allow you to specify one or more volumes that your Task requires during execution. It is recommended that Tasks uses at most one writeable Workspace. For example:

spec:
  steps:
    - name: write-message
      image: ubuntu
      script: |
        #!/usr/bin/env bash
        set -xe
        echo hello! > $(workspaces.messages.path)/message        
  workspaces:
    - name: messages
      description: The folder where we write the message to
      mountPath: /custom/path/relative/to/root

For more information, see Using Workspaces in Tasks and the Workspaces in a TaskRun example YAML file.

Propagated Workspaces

Workspaces can be propagated to embedded task specs, not referenced Tasks. For more information, see Propagated Workspaces.

Emitting Results

A Task is able to emit string results that can be viewed by users and passed to other Tasks in a Pipeline. These results have a wide variety of potential uses. To highlight just a few examples from the Tekton Catalog: the git-clone Task emits a cloned commit SHA as a result, the generate-build-id Task emits a randomized ID as a result, and the kaniko Task emits a container image digest as a result. In each case these results convey information for users to see when looking at their TaskRuns and can also be used in a Pipeline to pass data along from one Task to the next. Task results are best suited for holding small amounts of data, such as commit SHAs, branch names, ephemeral namespaces, and so on.

To define a Task's results, use the results field. In the example below, the Task specifies two files in the results field: current-date-unix-timestamp and current-date-human-readable.

apiVersion: tekton.dev/v1 # or tekton.dev/v1beta1
kind: Task
metadata:
  name: print-date
  annotations:
    description: |
            A simple task that prints the date
spec:
  results:
    - name: current-date-unix-timestamp
      description: The current date in unix timestamp format
    - name: current-date-human-readable
      description: The current date in human readable format
  steps:
    - name: print-date-unix-timestamp
      image: bash:latest
      script: |
        #!/usr/bin/env bash
        date +%s | tee $(results.current-date-unix-timestamp.path)        
    - name: print-date-human-readable
      image: bash:latest
      script: |
        #!/usr/bin/env bash
        date | tee $(results.current-date-human-readable.path)

In this example, $(results.name.path) is replaced with the path where Tekton will store the Task’s results.

When this Task is executed in a TaskRun, the results will appear in the TaskRun’s status:

apiVersion: tekton.dev/v1
kind: TaskRun
# ...
status:
  # ...
  results:
    - name: current-date-human-readable
      value: |
                Wed Jan 22 19:47:26 UTC 2020
    - name: current-date-unix-timestamp
      value: |
                1579722445

apiVersion: tekton.dev/v1beta1
kind: TaskRun
# ...
status:
  # ...
  taskResults:
    - name: current-date-human-readable
      value: |
                Wed Jan 22 19:47:26 UTC 2020
    - name: current-date-unix-timestamp
      value: |
                1579722445

Tekton does not perform any processing on the contents of results; they are emitted verbatim from your Task including any leading or trailing whitespace characters. Make sure to write only the precise string you want returned from your Task into the result files that your Task creates.

The stored results can be used at the Task level or at the Pipeline level.

Emitting Object Results

Emitting a task result of type object is implemented based on the TEP-0075. You can initialize object results from a task using JSON escaped string. For example, to assign the following data to an object result:

{"url":"abc.dev/sampler","digest":"19f02276bf8dbdd62f069b922f10c65262cc34b710eea26ff928129a736be791"}

You will need to use escaped JSON to write to pod termination message:

{\"url\":\"abc.dev/sampler\",\"digest\":\"19f02276bf8dbdd62f069b922f10c65262cc34b710eea26ff928129a736be791\"}

An example of a task definition producing an object result:

kind: Task
apiVersion: tekton.dev/v1 # or tekton.dev/v1beta1
metadata:
  name: write-object
  annotations:
    description: |
            A simple task that writes object
spec:
  results:
    - name: object-results
      type: object
      description: The object results
      properties:
        url:
          type: string
        digest:
          type: string
  steps:
    - name: write-object
      image: bash:latest
      script: |
        #!/usr/bin/env bash
        echo -n "{\"url\":\"abc.dev/sampler\",\"digest\":\"19f02276bf8dbdd62f069b922f10c65262cc34b710eea26ff928129a736be791\"}" | tee $(results.object-results.path)

Note:

  • that the opening and closing braces are mandatory along with an escaped JSON.
  • object result must specify the properties section to define the schema i.e. what keys are available for this object result. Failing to emit keys from the defined object results will result in validation error at runtime.

Emitting Array Results

Tekton Task also supports defining a result of type array and object in addition to string. Emitting a task result of type array is a beta feature implemented based on the TEP-0076. You can initialize array results from a task using JSON escaped string, for example, to assign the following list of animals to an array result:

["cat", "dog", "squirrel"]

You will have to initialize the pod termination message as escaped JSON:

[\"cat\", \"dog\", \"squirrel\"]

An example of a task definition producing an array result with such greetings ["hello", "world"]:

kind: Task
apiVersion: tekton.dev/v1 # or tekton.dev/v1beta1
metadata:
  name: write-array
  annotations:
    description: |
            A simple task that writes array
spec:
  results:
    - name: array-results
      type: array
      description: The array results
  steps:
    - name: write-array
      image: bash:latest
      script: |
        #!/usr/bin/env bash
        echo -n "[\"hello\",\"world\"]" | tee $(results.array-results.path)

Note that the opening and closing square brackets are mandatory along with an escaped JSON.

Now, similar to the Go zero-valued slices, an array result is considered as uninitialized (i.e. nil) if it’s set to an empty array i.e. []. For example, echo -n "[]" | tee $(results.result.path); is equivalent to result := []string{}. The result initialized in this way will have zero length. And trying to access this array with a star notation i.e. $(tasks.write-array-results.results.result[*]) or an element of such array i.e. $(tasks.write-array-results.results.result[0]) results in InvalidTaskResultReference with index out of range.

Depending on your use case, you might have to initialize a result array to the desired length just like using make() function in Go. make() function is used to allocate an array and returns a slice of the specified length i.e. result := make([]string, 5) results in ["", "", "", "", ""], similarly set the array result to following JSON escaped expression to allocate an array of size 2:

echo -n "[\"\", \"\"]" | tee $(results.array-results.path) # an array of size 2 with empty string
echo -n "[\"first-array-element\", \"\"]" | tee $(results.array-results.path) # an array of size 2 with only first element initialized
echo -n "[\"\", \"second-array-element\"]" | tee $(results.array-results.path) # an array of size 2 with only second element initialized
echo -n "[\"first-array-element\", \"second-array-element\"]" | tee $(results.array-results.path) # an array of size 2 with both elements initialized

This is also important to maintain the order of the elements in an array. The order in which the task result was initialized is the order in which the result is consumed by the dependent tasks. For example, a task is producing two array results images and configmaps. The pipeline author can implement deployment by indexing into each array result:

    - name: deploy-stage-1
      taskRef:
        name: deploy
      params:
        - name: image
          value: $(tasks.setup.results.images[0])
        - name: configmap
          value: $(tasks.setup.results.configmap[0])
      ...
    - name: deploy-stage-2
      taskRef:
        name: deploy
      params:
        - name: image
          value: $(tasks.setup.results.images[1])
        - name: configmap
          value: $(tasks.setup.results.configmap[1])

As a task author, make sure the task array results are initialized accordingly or set to a zero value in case of no image or configmap to maintain the order.

Note: Tekton uses termination messages. As written in tektoncd/pipeline#4808, the maximum size of a Task's results is limited by the container termination message feature of Kubernetes. At present, the limit is “4096 bytes”. This also means that the number of Steps in a Task affects the maximum size of a Result, as each Step is implemented as a container in the TaskRun’s pod. The more containers we have in our pod, the smaller the allowed size of each container’s message, meaning that the more steps you have in a Task, the smaller the result for each step can be. For example, if you have 10 steps, the size of each step’s Result will have a maximum of less than 1KB.

If your Task writes a large number of small results, you can work around this limitation by writing each result from a separate Step so that each Step has its own termination message. If a termination message is detected as being too large the TaskRun will be placed into a failed state with the following message: Termination message is above max allowed size 4096, caused by large task result. Since Tekton also uses the termination message for some internal information, so the real available size will less than 4096 bytes.

As a general rule-of-thumb, if a result needs to be larger than a kilobyte, you should likely use a Workspace to store and pass it between Tasks within a Pipeline.

Larger Results using sidecar logs

This is an alpha feature which is guarded behind its own feature flag. The results-from feature flag must be set to "sidecar-logs" to enable larger results using sidecar logs.

Instead of using termination messages to store results, the taskrun controller injects a sidecar container which monitors the results of all the steps. The sidecar mounts the volume where results of all the steps are stored. As soon as it finds a new result, it logs it to std out. The controller has access to the logs of the sidecar container. CAUTION: we need you to enable access to kubernetes pod/logs.

This feature allows users to store up to 4 KB per result by default. Because we are not limited by the size of the termination messages, users can have as many results as they require (or until the CRD reaches its limit). If the size of a result exceeds this limit, then the TaskRun will be placed into a failed state with the following message: Result exceeded the maximum allowed limit.

Note: If you require even larger results, you can specify a different upper limit per result by setting max-result-size feature flag to your desired size in bytes (see instructions). CAUTION: the larger you make the size, more likely will the CRD reach its max limit enforced by the etcd server leading to bad user experience.

Refer to the detailed instructions listed in additional config to learn how to enable this feature.

Specifying Volumes

Specifies one or more Volumes that the Steps in your Task require to execute in addition to volumes that are implicitly created for input and output resources.

For example, you can use Volumes to do the following:

  • Mount a Kubernetes Secret.
  • Create an emptyDir persistent Volume that caches data across multiple Steps.
  • Mount a Kubernetes ConfigMap as Volume source.
  • Mount a host’s Docker socket to use a Dockerfile for building container images. Note: Building a container image on-cluster using docker build is very unsafe and is mentioned only for the sake of the example. Use kaniko instead.

Specifying a Step template

The stepTemplate field specifies a Container configuration that will be used as the starting point for all of the Steps in your Task. Individual configurations specified within Steps supersede the template wherever overlap occurs.

In the example below, the Task specifies a stepTemplate field with the environment variable FOO set to bar. The first Step in the Task uses that value for FOO, but the second Step overrides the value set in the template with baz. Additional, the Task specifies a stepTemplate field with the environment variable TOKEN set to public. The last one Step in the Task uses private in the referenced secret to override the value set in the template.

stepTemplate:
  env:
    - name: "FOO"
      value: "bar"
    - name: "TOKEN"
      value: "public"
steps:
  - image: ubuntu
    command: [echo]
    args: ["FOO is ${FOO}"]
  - image: ubuntu
    command: [echo]
    args: ["FOO is ${FOO}"]
    env:
      - name: "FOO"
        value: "baz"
  - image: ubuntu
    command: [echo]
    args: ["TOKEN is ${TOKEN}"]
    env:
      - name: "TOKEN"
        valueFrom:
          secretKeyRef:
            key: "token"
            name: "test"
---
# The secret 'test' part data is as follows.
data:
  # The decoded value of 'cHJpdmF0ZQo=' is 'private'.
  token: "cHJpdmF0ZQo="

Specifying Sidecars

The sidecars field specifies a list of Containers to run alongside the Steps in your Task. You can use Sidecars to provide auxiliary functionality, such as Docker in Docker or running a mock API server that your app can hit during testing. Sidecars spin up before your Task executes and are deleted after the Task execution completes. For further information, see Sidecars in TaskRuns.

In the example below, a Step uses a Docker-in-Docker Sidecar to build a Docker image:

steps:
  - image: docker
    name: client
    script: |
      #!/usr/bin/env bash
      cat > Dockerfile << EOF
      FROM ubuntu
      RUN apt-get update
      ENTRYPOINT ["echo", "hello"]
      EOF
      docker build -t hello . && docker run hello
      docker images      
    volumeMounts:
      - mountPath: /var/run/
        name: dind-socket
sidecars:
  - image: docker:18.05-dind
    name: server
    securityContext:
      privileged: true
    volumeMounts:
      - mountPath: /var/lib/docker
        name: dind-storage
      - mountPath: /var/run/
        name: dind-socket
volumes:
  - name: dind-storage
    emptyDir: {}
  - name: dind-socket
    emptyDir: {}

Sidecars, just like Steps, can also run scripts:

sidecars:
  - image: busybox
    name: hello-sidecar
    script: |
            echo 'Hello from sidecar!'

Note: Tekton’s current Sidecar implementation contains a bug. Tekton uses a container image named nop to terminate Sidecars. That image is configured by passing a flag to the Tekton controller. If the configured nop image contains the exact command the Sidecar was executing before receiving a “stop” signal, the Sidecar keeps running, eventually causing the TaskRun to time out with an error. For more information, see issue 1347.

Specifying a display name

The displayName field is an optional field that allows you to add a user-facing name to the task that may be used to populate a UI.

Adding a description

The description field is an optional field that allows you to add an informative description to the Task.

Using variable substitution

Tekton provides variables to inject values into the contents of certain fields. The values you can inject come from a range of sources including other fields in the Task, context-sensitive information that Tekton provides, and runtime information received from a TaskRun.

The mechanism of variable substitution is quite simple - string replacement is performed by the Tekton Controller when a TaskRun is executed.

Tasks allow you to substitute variable names for the following entities:

See the complete list of variable substitutions for Tasks and the list of fields that accept substitutions.

Substituting parameters and resources

params and resources attributes can replace variable values as follows:

  • To reference a parameter in a Task, use the following syntax, where <name> is the name of the parameter: 
    # dot notation
# Here, the name cannot contain dots (eg. foo.bar is not allowed). If the name contains `dots`, it can only be accessed via the bracket notation.
$(params.<name> )
# or bracket notation (wrapping <name> with either single or double quotes):
# Here, the name can contain dots (eg. foo.bar is allowed).
$(params['<name>'])
$(params["<name>"])
  • To access parameter values from resources, see variable substitution

Substituting Array parameters

You can expand referenced parameters of type array using the star operator. To do so, add the operator ([*]) to the named parameter to insert the array elements in the spot of the reference string.

For example, given a params field with the contents listed below, you can expand command: ["first", "$(params.array-param[*])", "last"] to command: ["first", "some", "array", "elements", "last"]:

params:
  - name: array-param
    value:
      - "some"
      - "array"
      - "elements"

You must reference parameters of type array in a completely isolated string within a larger string array. Referencing an array parameter in any other way will result in an error. For example, if build-args is a parameter of type array, then the following example is an invalid Step because the string isn’t isolated:

- name: build-step
  image: gcr.io/cloud-builders/some-image
  args: ["build", "additionalArg $(params.build-args[*])"]

Similarly, referencing build-args in a non-array field is also invalid:

- name: build-step
  image: "$(params.build-args[*])"
  args: ["build", "args"]

A valid reference to the build-args parameter is isolated and in an eligible field (args, in this case):

- name: build-step
  image: gcr.io/cloud-builders/some-image
  args: ["build", "$(params.build-args[*])", "additionalArg"]

array param when referenced in args section of the step can be utilized in the script as command line arguments:

- name: build-step
  image: gcr.io/cloud-builders/some-image
  args: ["$(params.flags[*])"]
  script: |
    #!/usr/bin/env bash
    echo "The script received $# flags."
    echo "The first command line argument is $1."

Indexing into an array to reference an individual array element is supported as an alpha feature (enable-api-fields: alpha). Referencing an individual array element in args:

- name: build-step
  image: gcr.io/cloud-builders/some-image
  args: ["$(params.flags[0])"]

Referencing an individual array element in script:

- name: build-step
  image: gcr.io/cloud-builders/some-image
  script: |
    #!/usr/bin/env bash
    echo "$(params.flags[0])"

Substituting Workspace paths

You can substitute paths to Workspaces specified within a Task as follows:

$(workspaces.myworkspace.path)

Since the Volume name is randomized and only set when the Task executes, you can also substitute the volume name as follows:

$(workspaces.myworkspace.volume)

Substituting Volume names and types

You can substitute Volume names and types by parameterizing them. Tekton supports popular Volume types such as ConfigMap, Secret, and PersistentVolumeClaim. See this example to find out how to perform this type of substitution in your Task.

Substituting in Script blocks

Variables can contain any string, including snippets of script that can be injected into a Task’s Script field. If you are using Tekton’s variables in your Task’s Script field be aware that the strings you’re interpolating could include executable instructions.

Preventing a substituted variable from executing as code depends on the container image, language or shell that your Task uses. Here’s an example of interpolating a Tekton variable into a bash Script block that prevents the variable’s string contents from being executed:

# Task.yaml
spec:
  steps:
    - image: an-image-that-runs-bash
      env:
        - name: SCRIPT_CONTENTS
          value: $(params.script)
      script: |
                printf '%s' "${SCRIPT_CONTENTS}" > input-script

This works by injecting Tekton’s variable as an environment variable into the Step’s container. The printf program is then used to write the environment variable’s content to a file.

Code examples

Study the following code examples to better understand how to configure your Tasks:

_Tip: See the collection of Tasks in the Tekton community catalog for more examples.

Building and pushing a Docker image

The following example Task builds and pushes a Dockerfile-built image.

Note: Building a container image using docker build on-cluster is very unsafe and is shown here only as a demonstration. Use kaniko instead.

spec:
  params:
    # This may be overridden, but is a sensible default.
    - name: dockerfileName
      type: string
      description: The name of the Dockerfile
      default: Dockerfile
    - name: image
      type: string
      description: The image to build and push
  workspaces:
  - name: source
  steps:
    - name: dockerfile-build
      image: gcr.io/cloud-builders/docker
      workingDir: "$(workspaces.source.path)"
      args:
        [
          "build",
          "--no-cache",
          "--tag",
          "$(params.image)",
          "--file",
          "$(params.dockerfileName)",
          ".",
        ]
      volumeMounts:
        - name: docker-socket
          mountPath: /var/run/docker.sock

    - name: dockerfile-push
      image: gcr.io/cloud-builders/docker
      args: ["push", "$(params.image)"]
      volumeMounts:
        - name: docker-socket
          mountPath: /var/run/docker.sock

  # As an implementation detail, this Task mounts the host's daemon socket.
  volumes:
    - name: docker-socket
      hostPath:
        path: /var/run/docker.sock
        type: Socket

Mounting multiple Volumes

The example below illustrates mounting multiple Volumes:

spec:
  steps:
    - image: ubuntu
      script: |
        #!/usr/bin/env bash
        curl https://foo.com > /var/my-volume        
      volumeMounts:
        - name: my-volume
          mountPath: /var/my-volume

    - image: ubuntu
      script: |
        #!/usr/bin/env bash
        cat /etc/my-volume        
      volumeMounts:
        - name: my-volume
          mountPath: /etc/my-volume

  volumes:
    - name: my-volume
      emptyDir: {}

Mounting a ConfigMap as a Volume source

The example below illustrates how to mount a ConfigMap to act as a Volume source:

spec:
  params:
    - name: CFGNAME
      type: string
      description: Name of config map
    - name: volumeName
      type: string
      description: Name of volume
  steps:
    - image: ubuntu
      script: |
        #!/usr/bin/env bash
        cat /var/configmap/test        
      volumeMounts:
        - name: "$(params.volumeName)"
          mountPath: /var/configmap

  volumes:
    - name: "$(params.volumeName)"
      configMap:
        name: "$(params.CFGNAME)"

Using a Secret as an environment source

The example below illustrates how to use a Secret as an environment source:

apiVersion: tekton.dev/v1 # or tekton.dev/v1beta1
kind: Task
metadata:
  name: goreleaser
spec:
  params:
    - name: package
      type: string
      description: base package to build in
    - name: github-token-secret
      type: string
      description: name of the secret holding the github-token
      default: github-token
  workspaces:
  - name: source
  steps:
    - name: release
      image: goreleaser/goreleaser
      workingDir: $(workspaces.source.path)/$(params.package)
      command:
        - goreleaser
      args:
        - release
      env:
        - name: GOPATH
          value: /workspace
        - name: GITHUB_TOKEN
          valueFrom:
            secretKeyRef:
              name: $(params.github-token-secret)
              key: bot-token

Using a Sidecar in a Task

The example below illustrates how to use a Sidecar in your Task:

apiVersion: tekton.dev/v1 # or tekton.dev/v1beta1
kind: Task
metadata:
  name: with-sidecar-task
spec:
  params:
    - name: sidecar-image
      type: string
      description: Image name of the sidecar container
    - name: sidecar-env
      type: string
      description: Environment variable value
  sidecars:
    - name: sidecar
      image: $(params.sidecar-image)
      env:
        - name: SIDECAR_ENV
          value: $(params.sidecar-env)
  steps:
    - name: test
      image: hello-world

Debugging

This section describes techniques for debugging the most common issues in Tasks.

Inspecting the file structure

A common issue when configuring Tasks stems from not knowing the location of your data. For the most part, files ingested and output by your Task live in the /workspace directory, but the specifics can vary. To inspect the file structure of your Task, add a step that outputs the name of every file stored in the /workspace directory to the build log. For example:

- name: build-and-push-1
  image: ubuntu
  command:
    - /bin/bash
  args:
    - -c
    - |
      set -ex
      find /workspace

You can also choose to examine the contents of every file used by your Task:

- name: build-and-push-1
  image: ubuntu
  command:
    - /bin/bash
  args:
    - -c
    - |
      set -ex
      find /workspace | xargs cat

Inspecting the Pod

To inspect the contents of the Pod used by your Task at a specific stage in the Task's execution, log into the Pod and add a Step that pauses the Task at the desired stage. For example:

- name: pause
  image: docker
  args: ["sleep", "6000"]

Running Step Containers as a Non Root User

All steps that do not require to be run as a root user should make use of TaskRun features to designate the container for a step runs as a user without root permissions. As a best practice, running containers as non root should be built into the container image to avoid any possibility of the container being run as root. However, as a further measure of enforcing this practice, steps can make use of a securityContext to specify how the container should run.

An example of running Task steps as a non root user is shown below:

apiVersion: tekton.dev/v1 # or tekton.dev/v1beta1
kind: Task
metadata:
  name: show-non-root-steps
spec:
  steps:
    # no securityContext specified so will use
    # securityContext from TaskRun podTemplate
    - name: show-user-1001
      image: ubuntu
      command:
        - ps
      args:
        - "aux"
    # securityContext specified so will run as
    # user 2000 instead of 1001
    - name: show-user-2000
      image: ubuntu
      command:
        - ps
      args:
        - "aux"
      securityContext:
        runAsUser: 2000
---
apiVersion: tekton.dev/v1 # or tekton.dev/v1beta1
kind: TaskRun
metadata:
  generateName: show-non-root-steps-run-
spec:
  taskRef:
    name: show-non-root-steps
  podTemplate:
    securityContext:
      runAsNonRoot: true
      runAsUser: 1001

In the example above, the step show-user-2000 specifies via a securityContext that the container for the step should run as user 2000. A securityContext must still be specified via a TaskRun podTemplate for this TaskRun to run in a Kubernetes environment that enforces running containers as non root as a requirement.

The runAsNonRoot property specified via the podTemplate above validates that steps part of this TaskRun are running as non root users and will fail to start any step container that attempts to run as root. Only specifying runAsNonRoot: true will not actually run containers as non root as the property simply validates that steps are not running as root. It is the runAsUser property that is actually used to set the non root user ID for the container.

If a step defines its own securityContext, it will be applied for the step container over the securityContext specified at the pod level via the TaskRun podTemplate.

More information about Pod and Container Security Contexts can be found via the Kubernetes website.

The example Task/TaskRun above can be found as a TaskRun example.

Task Authoring Recommendations

Recommendations for authoring Tasks are available in the Tekton Catalog.

Except as otherwise noted, the contents of this page are licensed under the Creative Commons Attribution 4.0 License. Code samples are licensed under the Apache 2.0 License.