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Results Lifecycle

This section gives an overview of the results lifecycle in Tekton Pipelines.

Results definition and usage

Tasks can define results by adding a result on the Task spec. For more information, see "Emitting Results". Users are encouraged to use variable substitution for Result paths (i.e. writing to $(results.name.path)), but can also write to the /tekton/results directory directly, for example:

apiVersion: tekton.dev/v1beta1
kind: Task
metadata:
  name: print-date
  annotations:
    description: |
      A simple task that prints the date to make sure your cluster / Tekton is working properly.
spec:
  results:
    - name: "current-date"
      description: "The current date"
  steps:
    - name: print-date
      image: bash:latest
      args:
        - "-c"
        - |
          date > /tekton/results/current-date

The result is added to a file name with the specified result's name into the /tekton/results folder. This is then added to the task run status. Internally the results are a new argument -resultsto the entrypoint defined for the task.

Each results entry in the Task's YAML corresponds to a file that the Task should stores the result in. When a Task specifies results, the TaskRun reconciler automatically creates the /tekton/results directory using an emptyDir volume and mounts it on all the step containers. When the script is run inside the container, the results will be available accordingly.

Users can also refer to Task results in Pipeline Tasks. See "Passing one Task's Results into the Parameters or when expressions of another" for more information.

Known issues

Here are the important functions that come into play in the TaskRun reconciler:

  1. Attaching volumes and creating the step containers.

Inside the step container

After the execution of the script in the step, the entrypointer jsonifies and then copies the results from /tekton/results to the termination path /tekton/termination. Just before the copy, the 4KB limit is checked and an error is thrown in the container logs if the size exceeds 4 KB. The kubernetes extracts the information from the termination path and provides it to the user as pod.State.Terminated.Message.

Here are the important functions that come into play:

  1. Entrypointer copies results to termination path and enforces 4K limit

The taskrun reconciler

The taskrun reconciler executes a periodic loop performing multiple actions depending on the status of the taskrun. Once such action is reconcile. In this action, the reconciler extracts the termination message from the state of the pods (State.Terminated.Message). The message string is then parsed and the results are extracted and attached to the taskrun's status from where it can used by future tasks or accessed by the user.

Here are the important functions that come into play:

  1. Reconciler extracts the results from termination message and updates taskrun status