runner/docs/adrs/0549-composite-run-steps.md

ADR 054x: Composite Run Steps

Date: 2020-06-17

Status: Proposed

Relevant PR: https://github.com/actions/runner/pull/549

Context

Customers want to be able to compose actions from actions (ex: https://github.com/actions/runner/issues/438)

An important step towards meeting this goal is to build in functionality for actions where users can simply execute any number of steps.

Guiding Principles

We don't want the workflow author to need to know how the internal workings of the action work. Users shouldn't know the internal workings of the composite action (for example, default.shell and default.workingDir should not be inherited from the workflow file to the action file). When deciding how to design certain parts of composite run steps, we want to think one logical step from the consumer.

A composite action is treated as one individual job step (aka encapsulation).

Decision

In this ADR, we only support running multiple run steps in an Action. In doing so, we build in support for mapping and flowing the inputs, outputs, and env variables (ex: All nested steps should have access to its parents' input variables and nested steps can overwrite the input variables).

Steps

Example workflow.yml

jobs:
  build:
    runs-on: self-hosted
    steps:
    - id: step1
      uses: actions/setup-python@v1
    - id: step2
      uses: actions/setup-node@v2
    - uses: actions/checkout@v2
    - uses: user/composite@v1
    - name: workflow step 1
      run: echo hello world 3
    - name: workflow step 2
      run: echo hello world 4

Example user/composite/action.yml

runs:
  using: "composite"
  steps:
    - run: pip install -r requirements.txt
    - run: npm install

Example Output

[npm installation output]
[pip requirements output]
echo hello world 3
echo hello world 4

We add a token called "composite" which allows our Runner code to process composite actions. By invoking "using: composite", our Runner code then processes the "steps" attribute, converts this template code to a list of steps, and finally runs each run step sequentially. If any step fails and there are no if conditions defined, the whole composite action job fails.

Inputs

Example workflow.yml:

steps: 
  - id: foo
    uses: user/composite@v1
    with:
      your_name: "Octocat"

Example user/composite/action.yml:

inputs:
  your_name:
    description: 'Your name'
    default: 'Ethan'
runs:
  using: "composite"
  steps: 
    - run: echo hello ${{ inputs.your_name }}

Example Output:

hello Octocat

Each input variable in the composite action is only viewable in its own scope.

Outputs

Example workflow.yml:

...
steps: 
  - id: foo
    uses: user/composite@v1
  - run: echo random-number ${{ steps.foo.outputs.random-number }} 

Example user/composite/action.yml:

outputs:
  random-number: 
    description: "Random number"
    value: ${{ steps.random-number-generator.outputs.random-id }}
runs:
  using: "composite"
  steps: 
    - id: random-number-generator
      run: echo "::set-output name=random-number::$(echo $RANDOM)"

Example Output:

::set-output name=my-output::43243
random-number 43243

Each of the output variables from the composite action is viewable from the workflow file that uses the composite action. In other words, every child action output(s) is viewable only by its parent using dot notation (ex steps.foo.outputs.random-number).

Moreover, the output ids are only accessible within the scope where it was defined. Note that in the example above, in our workflow.yml file, it should not have access to output id (i.e. random-id). The reason why we are doing this is because we don't want to require the workflow author to know the internal workings of the composite action.

Context

Similar to the workflow file, the composite action has access to the same context objects (ex: github, env, strategy).

Environment

In the Composite Action, you'll only be able to use ::set-env:: to set environment variables just like you could with other actions.

Secrets

Note : This feature will be focused on in a future ADR.

We'll pass the secrets from the composite action's parents (ex: the workflow file) to the composite action. Secrets can be created in the composite action with the secrets context. In the actions yaml, we'll automatically mask the secret.

If Condition

Example workflow.yml:

steps:
  - run: exit 1
  - uses: user/composite@v1  # <--- this will run, as it's marked as always runing
    if: always()

Example user/composite/action.yml:

runs:
  using: "composite"
  steps:
    - run: echo "just succeeding"
    - run: echo "I will run, as my current scope is succeeding"
      if: success()
    - run: exit 1
    - run: echo "I will not run, as my current scope is now failing"

See the paragraph below for a rudimentary approach (thank you to @cybojenix for the idea, example, and explanation for this approach):

The if statement in the parent (in the example above, this is the workflow.yml) shows whether or not we should run the composite action. So, our composite action will run since the if condition for running the composite action is always().

Note that the if condition on the parent does not propogate to the rest of its children though.

In the child action (in this example, this is the action.yml), it starts with a clean slate (in other words, no imposing if conditions). Similar to the logic in the paragraph above, echo "I will run, as my current scope is succeeding" will run since the if condition checks if the previous steps within this composite action has not failed. run: echo "I will not run, as my current scope is now failing" will not run since the previous step resulted in an error and by default, the if expression is set to success() if the if condition is not set for a step.

What if a step has cancelled()? We do the opposite of our approach above if cancelled() is used for any of our composite run steps. We will cancel any step that has this condition if the workflow is cancelled at all.

Timeout-minutes

Example workflow.yml:

steps: 
  - id: bar
    uses: user/test@v1
    timeout-minutes: 50

Example user/composite/action.yml:

runs:
  using: "composite"
  steps: 
    - id: foo1
      run: echo test 1
      timeout-minutes: 10
    - id: foo2
      run: echo test 2
    - id: foo3
      run: echo test 3
      timeout-minutes: 10

A composite action in its entirety is a job. You can set both timeout-minutes for the whole composite action or its steps as long as the the sum of the timeout-minutes for each composite action step that has the attribute timeout-minutes is less than or equals to timeout-minutes for the composite action. There is no default timeout-minutes for each composite action step.

If the time taken for any of the steps in combination or individually exceed the whole composite action timeout-minutes attribute, the whole job will fail (1). If an individual step exceeds its own timeout-minutes attribute but the total time that has been used including this step is below the overall composite action timeout-minutes, the individual step will fail but the rest of the steps will run based on their own timeout-minutes attribute (they will still abide by condition (1) though).

For reference, in the example above, if the composite step foo1 takes 11 minutes to run, that step will fail but the rest of the steps, foo1 and foo2, will proceed as long as their total runtime with the previous failed foo1 action is less than the composite action's timeout-minutes (50 minutes). If the composite step foo2 takes 51 minutes to run, it will cause the whole composite action job to fail. I

The rationale behind this is that users can configure their steps with the if condition to conditionally set how steps rely on each other. Due to the additional capabilities that are offered with combining timeout-minutes and/or if, we wanted the timeout-minutes condition to be as dumb as possible and not effect other steps.

Usage limits still apply

Continue-on-error

Example workflow.yml:

steps: 
  - run: exit 1
  - id: bar
    uses: user/test@v1
    continue-on-error: false
  - id: foo
    run: echo "Hello World" <------- This step will not run

Example user/composite/action.yml:

runs:
  using: "composite"
  steps: 
    - run: exit 1
      continue-on-error: true
    - run: echo "Hello World 2" <----- This step will run

If any of the steps fail in the composite action and the continue-on-error is set to false for the whole composite action step in the workflow file, then the steps below it will run. On the flip side, if continue-on-error is set to true for the whole composite action step in the workflow file, the next job step will run.

For the composite action steps, it follows the same logic as above. In this example, "Hello World 2" will be outputted because the previous step has continue-on-error set to true although that previous step errored.

Defaults

The composite action author will be required to set the shell and workingDir of the composite action. Moreover, the composite action author will be able to explicitly set the shell for each composite run step. The workflow author will not have the ability to change these attributes.

Visualizing Composite Action in the GitHub Actions UI

We want all the composite action's steps to be condensed into the original composite action node.

Here is a visual represenation of the first example

| composite_action_node |
    | echo hello world 1 | 
    | echo hello world 2 |
| echo hello world 3 | 
| echo hello world 4 |

Conclusion

This ADR lays the framework for eventually supporting nested Composite Actions within Composite Actions. This ADR allows for users to run multiple run steps within a GitHub Composite Action with the support of inputs, outputs, environment, and context for use in any steps as well as the if, timeout-minutes, and the continue-on-error attributes for each Composite Action step.