TEP-0090: Matrix - Failure Strategies

[TEP-0090: Matrix][tep-0090] proposed executing a `PipelineTask` in
parallel `TaskRuns` and `Runs` with substitutions from combinations
of `Parameters` in a `Matrix`.

In this change, we propose a fail-fast stategy for handling failures
in `TaskRuns` and `Runs` created from a `Matrix`. This makes it easier
to control the execution of the many `TaskRuns` or `Runs` created from
a `Matrix` - up to 256.

This approach also aligns with the default behavior of `Matrix` in
other Continuous Delivery systems e.g [GitHub Actions][ghm-failfast].

If needed, we can explore supporting other failure strategies later.

[tep-0090]: https://github.com/tektoncd/community/blob/main/teps/0090-matrix.md
[ghm-failfast]: https://docs.github.com/en/actions/using-jobs/using-a-matrix-for-your-jobs#handling-failures

Author: jerop

teps/0090-matrix.md

@@ -2,7 +2,7 @@
 status: implementable
 title: Matrix
 creation-date: '2021-10-13'
-last-updated: '2022-02-14'
+last-updated: '2022-06-09'
 authors:
 - '@jerop'
 - '@pritidesai'
@@ -42,6 +42,7 @@ see-also:
       - [Alternatives](#alternatives)
   - [Fan Out](#fan-out)
   - [Concurrency Control](#concurrency-control)
+  - [Failure Strategies](#failure-strategies)
 - [Design](#design)
   - [Parameters](#parameters)
     - [Substituting String Parameters in the Tasks](#substituting-string-parameters-in-the-tasks)
@@ -206,18 +207,16 @@ specified in a `matrix`.
 
 The following are out of scope for this TEP:
 
-1. Terminating early when one of the `TaskRuns` or `Runs` created in parallel fails. As is currently, running `TaskRuns` 
-and `Runs` have to complete execution before termination.
-2. Controlling the concurrency of `TaskRuns` or `Runs` created in a given `matrix`. This will be addressed more broadly 
+1. Controlling the concurrency of `TaskRuns` or `Runs` created in a given `matrix`. This will be addressed more broadly 
 in Tekton Pipelines ([tektoncd/pipeline: issue#2591][issue-2591], [tektoncd/experimental: issue#804][issue-804]).
-3. Configuring the `TaskRuns` or `Runs` created in a given `matrix` to execute sequentially. This remains an option that 
+2. Configuring the `TaskRuns` or `Runs` created in a given `matrix` to execute sequentially. This remains an option that 
 we can explore later.
-4. Excluding generating a `TaskRun` or `Run` for a specific combination in the `matrix`. This can be handled using 
+3. Excluding generating a `TaskRun` or `Run` for a specific combination in the `matrix`. This can be handled using 
 guarded execution through `when` expressions. This remains an option we can explore later if needed.
-5. Including generating a `TaskRun` or `Run` for a specific combination in the `matrix`. This can be handled by adding 
+4. Including generating a `TaskRun` or `Run` for a specific combination in the `matrix`. This can be handled by adding 
 the items that produce that combination into the `matrix`, and using guarded execution through `when` expressions to 
 exclude the combinations that should be skipped. This remains an option we can explore later if needed.
-6. Supporting producing `Results` from fanned out `PipelineTasks`. We plan to address this after [TEP-0075][tep-0075]
+5. Supporting producing `Results` from fanned out `PipelineTasks`. We plan to address this after [TEP-0075][tep-0075]
 and [TEP-0076][tep-0076] have landed. 
 
 ### Requirements
@@ -721,6 +720,18 @@ If needed, we can also explore providing more granular controls for maximum numb
 or `Runs` from `Matrices` - either at `PipelineRun`, `Pipeline` or `PipelineTask` levels - later.
 This is an option we can pursue after gathering user feedback - it's out of scope for this TEP.
 
+### Failure Strategies
+
+In failure scenarios, the `TaskRuns` or `Runs` created from a `Matrix` will fail fast. That is, when
+any `TaskRun` or `Run` from a given fanned-out `PipelineTask` fails or is cancelled then the other
+`TaskRuns` or `Runs` from the same `PipelineTask` will be cancelled.
+
+This approach makes it easier to control the execution of the many `TaskRuns` or `Runs` that can be
+created from a `Matrix` (up to 256 for now). Moreover, failing fast is the default behavior of `Matrix`
+in other Continuous Delivery systems - see [GitHub Actions - Handling Failures in Matrix][ghm-failfast].
+
+If needed, we can explore supporting other failure strategies later. 
+
 ## Design 
 
 In this section, we go into the details of the `Matrix` in relation to:
@@ -1650,4 +1661,5 @@ However, this approach has the following disadvantages:
 [git-clone]: https://github.com/tektoncd/catalog/tree/main/task/git-clone/0.5
 [when]: https://github.com/tektoncd/pipeline/blob/6cb0f4ccfce095495ca2f0aa20e5db8a791a1afe/docs/pipelines.md#guard-task-execution-using-when-expressions
 [retries]: https://github.com/tektoncd/pipeline/blob/6cb0f4ccfce095495ca2f0aa20e5db8a791a1afe/docs/pipelines.md#using-the-retries-parameter
-[timeouts]: https://github.com/tektoncd/pipeline/blob/6cb0f4ccfce095495ca2f0aa20e5db8a791a1afe/docs/pipelines.md#configuring-the-failure-timeout
+[timeouts]: https://github.com/tektoncd/pipeline/blob/6cb0f4ccfce095495ca2f0aa20e5db8a791a1afe/docs/pipelines.md#configuring-the-failure-timeout
+[ghm-failfast]: https://docs.github.com/en/actions/using-jobs/using-a-matrix-for-your-jobs#handling-failures

teps/README.md

@@ -234,7 +234,7 @@ This is the complete list of Tekton teps:
 |[TEP-0086](0086-changing-the-way-result-parameters-are-stored.md) | Changing the way result parameters are stored | proposed | 2022-04-07 |
 |[TEP-0088](0088-result-summaries.md) | Tekton Results - Record Summaries | proposed | 2021-10-01 |
 |[TEP-0089](0089-nonfalsifiable-provenance-support.md) | Non-falsifiable provenance support | implementable | 2022-01-18 |
-|[TEP-0090](0090-matrix.md) | Matrix | implementable | 2022-02-14 |
+|[TEP-0090](0090-matrix.md) | Matrix | implementable | 2022-06-09 |
 |[TEP-0092](0092-scheduling-timeout.md) | Scheduling Timeout | implementable | 2022-04-11 |
 |[TEP-0094](0094-configuring-resources-at-runtime.md) | Configuring Resources at Runtime | implemented | 2022-03-11 |
 |[TEP-0095](0095-common-repository-configuration.md) | Common Repository Configuration | proposed | 2021-11-29 |