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CustomRuns

Overview

v1beta1.CustomRun has replaced v1alpha1.Run for executing Custom Tasks. Please refer to the migration doc for details on updating v1alpha1.Run to v1beta1.CustomRun before upgrading to a release that does not support v1alpha1.Run.

A CustomRun allows you to instantiate and execute a Custom Task, which can be implemented by a custom task controller running on-cluster. Custom Tasks can implement behavior that's independent of how Tekton TaskRun is implemented.

In order for a CustomRun to actually execute, there must be a custom task controller running on the cluster that is responsible for watching and updating CustomRuns which reference their type. If no such controller is running, CustomRuns will have no .status value and no further action will be taken.

Configuring a CustomRun

A CustomRun definition supports the following fields:

  • Required:
    • apiVersion - Specifies the API version. Currently,only tekton.dev/v1beta1 is supported.
    • kind - Identifies this resource object as a CustomRun object.
    • metadata - Specifies the metadata that uniquely identifies the CustomRun, such as a name.
    • spec - Specifies the configuration for the CustomRun.
      • customRef - Specifies the type and (optionally) name of the custom task type to execute.
      • customSpec - Embed the custom task resource spec directly in a CustomRun.
  • Optional:
    • timeout - specifies the maximum duration of a single execution of a CustomRun.
    • retries - specifies the number of retries to execute upon CustomRunfailure.
    • params - Specifies the desired execution parameters for the custom task.
    • serviceAccountName - Specifies a ServiceAccount object for executing the CustomRun.
    • workspaces - Specifies the physical volumes to use for the Workspaces required by a custom task.

Specifying the target Custom Task

A custom task resource's CustomSpec may be directly embedded in the CustomRun or it may be referred to by a CustomRef. But, not both at the same time.

  1. Specifying the target Custom Task with customRef Referring a custom task (i.e. CustomRef ) promotes reuse of custom task definitions.

  2. Specifying the target Custom Task by embedding its spec Embedding a custom task (i.e. CustomSpec ) helps in avoiding name collisions with other users within the same namespace. Additionally, in a pipeline with multiple embedded custom tasks, the details of entire pipeline can be fetched in a single API request.

Specifying the target Custom Task with customRef

To specify the custom task type you want to execute in your CustomRun, use the customRef field as shown below:

apiVersion: tekton.dev/v1beta1
kind: CustomRun
metadata:
  name: my-example-run
spec:
  customRef:
    apiVersion: example.dev/v1beta1
    kind: MyCustomKind
  params:
  - name: duration
    value: 10s

When this CustomRun is created, the Custom Task controller responsible for reconciling objects of kind "MyCustomKind" in the "example.dev/v1beta1" api group will execute it based on the input params.

You can also specify the name and optional namespace (default is default) of a custom task resource object previously defined in the cluster.

apiVersion: tekton.dev/v1beta1
kind: CustomRun
metadata:
  name: my-example-run
spec:
  customRef:
    apiVersion: example.dev/v1beta1
    kind: Example
    name: an-existing-example-task

If the customRef specifies a name, the custom task controller should look up the Example resource with that name, and use that object to configure the execution.

If the customRef does not specify a name, the custom task controller might support some default behavior for executing unnamed tasks.

In either case, if the named resource cannot be found, or if unnamed tasks are not supported, the custom task controller should update the CustomRun's status to indicate the error.

Specifying the target Custom Task by embedding its customSpec

To specify the custom task spec, it can be embedded directly into a CustomRun's spec as shown below:

apiVersion: tekton.dev/v1beta1
kind: CustomRun
metadata:
  name: embedded-run
spec:
  customSpec:
    apiVersion: example.dev/v1beta1
    kind: Example
    spec:
      field1: value1
      field2: value2

When this CustomRun is created, the custom task controller responsible for reconciling objects of kind Example in the example.dev api group will execute it.

Developer guide for custom controllers supporting customSpec.

  1. A custom controller may or may not support a Spec. In cases where it is not supported the custom controller should respond with proper validation error.

  2. Validation of the fields of the custom task is delegated to the custom task controller. It is recommended to implement validations as asynchronous (i.e. at reconcile time), rather than part of the webhook. Using a webhook for validation is problematic because, it is not possible to filter custom task resource objects before validation step, as a result each custom task resource has to undergo validation by all the installed custom task controllers.

  3. A custom task may have an empty spec, but cannot have an empty ApiVersion and Kind. Custom task controllers should handle an empty spec, either with a default behaviour, in a case no default behaviour is supported then, appropriate validation error should be updated to the CustomRun's status.

Cancellation

The custom task is responsible for implementing cancellation to support pipelineRun level timeouts and cancellation. If the Custom Task implementor does not support cancellation via .spec.status, Pipeline can not timeout within the specified interval/duration and can not be cancelled as expected upon request.

Pipeline Controller sets the spec.Status and spec.StatusMessage to signal CustomRuns about the Cancellation, while CustomRun controller updates its status.conditions as following once noticed the change on spec.Status.

status
  conditions:
  - type: Succeeded
    status: False
    reason: CustomRunCancelled

Specifying Timeout

A custom task specification can be created with Timeout as follows:

apiVersion: tekton.dev/v1beta1
kind: CustomRun
metadata:
  generateName: simpleexample
spec:
  timeout: 10s # set timeouts here.
  params:
    - name: searching
      value: the purpose of my existence
  customRef:
    apiVersion: custom.tekton.dev/v1alpha1
    kind: Example
    name: exampleName

Supporting timeouts is optional but recommended.

Developer guide for custom controllers supporting Timeout

  1. Tekton controllers will never directly update the status of the CustomRun, it is the responsibility of the custom task controller to support timeout. If timeout is not supported, it's the responsibility of the custom task controller to reject CustomRuns that specify a timeout value.
  2. When CustomRun.Spec.Status is updated to RunCancelled, the custom task controller MUST cancel the CustomRun. Otherwise, pipeline-level Timeout and Cancellation won't work for the Custom Task.
  3. A Custom Task controller can watch for this status update (i.e. CustomRun.Spec.Status == RunCancelled) and or CustomRun.HasTimedOut() and take any corresponding actions (i.e. a clean up e.g., cancel a cloud build, stop the waiting timer, tear down the approval listener).
  4. Once resources or timers are cleaned up, while it is REQUIRED to set a conditions on the CustomRun's status of Succeeded/False with an optional Reason of CustomRunTimedOut.
  5. Timeout is specified for each retry attempt instead of all retries.

Specifying Retries

A custom task specification can be created with Retries as follows:

apiVersion: tekton.dev/v1beta1
kind: CustomRun
metadata:
  generateName: simpleexample
spec:
  retries: 3 # set retries
  params:
    - name: searching
      value: the purpose of my existence
  customRef:
    apiVersion: custom.tekton.dev/v1alpha1
    kind: Example
    name: exampleName

Supporting retries is optional but recommended.

Developer guide for custom controllers supporting retries

  1. Tekton controller only depends on ConditionSucceeded to determine the termination status of a CustomRun, therefore Custom task implementors MUST NOT set ConditionSucceeded to False until all retries are exhausted.
  2. Those custom tasks who do not wish to support retry, can simply ignore it.
  3. It is recommended, that custom task should update the field RetriesStatus of a CustomRun on each retry performed by the custom task.
  4. Tekton controller does not validate that number of entries in RetriesStatus is same as specified value of retries count.

Specifying Parameters

If a custom task supports parameters, you can use the params field in the CustomRun to specify their values:

spec:
  params:
    - name: my-param
      value: chicken

If the custom task controller knows how to interpret the parameter value, it will do so. It might enforce that some parameter values must be specified, or reject unknown parameter values.

Specifying workspaces

If the custom task supports it, you can provide Workspaces to share data with the custom task .

spec:
  workspaces:
    - name: my-workspace
      emptyDir: {}

Consult the documentation of the custom task that you are using to determine whether it supports workspaces and how to name them.

Specifying a ServiceAccount

If the custom task supports it, you can execute the CustomRun with a specific set of credentials by specifying a ServiceAccount object name in the serviceAccountName field in your CustomRun definition. If you do not explicitly specify this, the CustomRun executes with the service account specified in the configmap-defaults ConfigMap. If this default is not specified, CustomRuns will execute with the default service account set for the target namespace.

spec:
  serviceAccountName: my-account

Consult the documentation of the custom task that you are using to determine whether it supports a service account name.

Monitoring execution status

As your CustomRun executes, its status field accumulates information on the execution of the CustomRun. This information includes the current state of the CustomRun, start and completion times, and any output results reported by the custom task controller.

Status Reporting

When the CustomRun<Example> is validated and created, the Custom Task controller will be notified and is expected to begin doing some operation. When the operation begins, the controller MUST update the CustomRun's .status.conditions to report that it's ongoing:

status
  conditions:
  - type: Succeeded
    status: Unknown

When the operation completes, if it was successful, the condition MUST report status: True, and optionally a brief reason and human-readable message:

status
  conditions:
  - type: Succeeded
    status: True
    reason: ExampleComplete # optional
    message: Yay, good times # optional

If the operation was unsuccessful, the condition MUST report status: False, and optionally a reason and human-readable message:

status
  conditions:
  - type: Succeeded
    status: False
    reason: ExampleFailed # optional
    message: Oh no bad times # optional

If the CustomRun was cancelled, the condition MUST report status: False, reason: CustomRunCancelled, and optionally a human-readable message:

status
  conditions:
  - type: Succeeded
    status: False
    reason: CustomRunCancelled
    message: Oh it's cancelled # optional

The following tables shows the overall status of a CustomRun:

status Description
The custom task controller has not taken any action on the CustomRun.
Unknown The custom task controller has started execution and the CustomRun is ongoing.
True The CustomRun completed successfully.
False The CustomRun completed unsuccessfully, and all retries were exhausted.

The CustomRun type's .status will also allow controllers to report other fields, such as startTime, completionTime, results (see below), and arbitrary context-dependent fields the Custom Task author wants to report. A fully-specified CustomRun status might look like:

status
  conditions:
  - type: Succeeded
    status: True
    reason: ExampleComplete
    message: Yay, good times
  completionTime: "2020-06-18T11:55:01Z"
  startTime: "2020-06-18T11:55:01Z"
  results:
  - name: first-name
    value: Bob
  - name: last-name
    value: Smith
  arbitraryField: hello world
  arbitraryStructuredField:
    listOfThings: ["a", "b", "c"]

Monitoring Results

After the CustomRun completes, the custom task controller can report output values in the results field:

results:
- name: my-result
  value: chicken

Code examples

To better understand CustomRuns, study the following code examples:

Example CustomRun with a referenced custom task

In this example, a CustomRun named my-example-run invokes a custom task of the v1alpha1 version of the Example kind in the example.dev API group, with the name my-example-task.

In this case the custom task controller is expected to look up the Example resource named my-example-task and to use that configuration to configure the execution of the CustomRun.

apiVersion: tekton.dev/v1beta1
kind: CustomRun
metadata:
  name: my-example-run
spec:
  customRef:
    apiVersion: example.dev/v1alpha1
    kind: Example
    name: my-example-task

Example CustomRun with an unnamed custom task

In this example, a CustomRun named my-example-run invokes a custom task of the v1alpha1 version of the Example kind in the example.dev API group, without a specified name.

In this case the custom task controller is expected to provide some default behavior when the referenced task is unnamed.

apiVersion: tekton.dev/v1beta1
kind: CustomRun
metadata:
  name: my-example-run
spec:
  customRef:
    apiVersion: example.dev/v1alpha1
    kind: Example

Example of specifying parameters

In this example, a CustomRun named my-example-run invokes a custom task, and specifies some parameter values to further configure the execution's behavior.

In this case the custom task controller is expected to validate and interpret these parameter values and use them to configure the CustomRun's execution.

apiVersion: tekton.dev/v1alpha1
kind: CustomRun
metadata:
  name: my-example-run
spec:
  customRef:
    apiVersion: example.dev/v1alpha1
    kind: Example
    name: my-example-task
  params:
    - name: my-first-param
      value: i'm number one
    - name: my-second-param
      value: close second