Adding or removing activities after the Workflow is started

[im-Clement]

Hello,

Thank you for the great package.

Is there a way to add new activities (or remove some of the existing ones) after the workflow is started?

[rmcdaniel]

If all you do is add something to the workflow at the end, you should be okay. You just stop the queue workers, deploy the new code and restart the workers with the new code. If you make changes that would replace or remove activities then that would probably break the workflow.

An upcoming feature will be to add WorkflowStub::getVersion() to enable versioning support.

public static function getVersion(string $changeId, int $minSupported, int $maxSupported);

Here's a quick breakdown of the parameters:

• $changeId: A unique identifier for the change you're making in the workflow. For example, if you're modifying a step in your workflow, this could be something like 'Step1'.
• $minSupported: The lowest version number of your workflow that's still supported. If an older version of a workflow tries to run with a minSupported value higher than its version, it would fail.
• $maxSupported: The highest or latest version number of your workflow that's supported.

The function would return an integer representing the current version number for the given change. It would allow Laravel Workflow to keep track of different stages of changes and manage them accordingly.

Here's a hypothetical example:

public function execute()
{
    $result1 = yield ActivityStub::make(ActivityA::class);
    $result2 = yield ActivityStub::make(ActivityB::class);

    return $result2;
}

Say we have a workflow that uses ActivityA. Now we need to replace ActivityA with ActivityC in an update. This change can be challenging if a workflow has already started, right? But with our proposed method, the system could be smart enough to understand the change and adapt accordingly.

public function execute()
{
    $v = yield WorkflowStub::getVersion('Step1', WorkflowStub::DEFAULT_VERSION, 1);

    if ($v === WorkflowStub::DEFAULT_VERSION) {
        $result1 = yield ActivityStub::make(ActivityA::class);
    } else {
        $result1 = yield ActivityStub::make(ActivityC::class);
    }

    $result2 = yield ActivityStub::make(ActivityB::class);

    return $result2;
}

A workflow that has already started and completed ActivityA would return DEFAULT_VERSION but a new workflow that hasn't started and completed ActivityA would return version = 1 and therefore run ActivityC instead.

Would this accomplish what you're asking?

[im-Clement]

Thank you for the detailed answer.

That versioning support seems to be something very useful.

In my case, I need to be able to programmatically append new activities without changing the Workflow code.

Probably at this point, the best way to do that is to start an entirely new workflow and continue with the base one after the new one is completed, using a signal method.

As an example

class MyInitialWorkflow extends Workflow
{
    public function execute()
    {
        return [
           yield ActivityStub::make(MyActivityA::class),
           yield WorkflowStub::await(fn () => $this->awaitA);
           yield ActivityStub::make(MyActivityB::class),
        ];
    }
}

Then, during, MyActivityA it is decided we need to fire a new MySecondActivityA, based on a specific API response we get.

In that case, I am thinking to start a new MySecondWorkflow for running MySecondActivityA.

When the MySecondActivityA is done, it will fire the $awaitA signal so MyInitialWorkflow will continue from the there with MyActivityB.

The downside for this approach seems to be in monitoring as the entire process is spread over multiple workflows.

Does this make sens from the Laravel Workflows logic perspective?

[rmcdaniel]

@im-Clement Ah I see what you mean now. I think if you keep the list of activities in an array you could add to the array using a signal.

class MyWorkflow extends Workflow
{
    protected $activities = [];

    #[SignalMethod]
    public function addActivity($activity)
    {
        $this->activities[] = $activity;
    }

    public function execute()
    {
        $this->activities = [
            MyActivityA::class,
            MyActivityB::class,
        ];

        foreach ($this->activities as $activity) {
            yield ActivityStub::make($activity);
        }
    }
}

While the workflow is running you can signal it like this to add a new activity.

$workflow = WorkflowStub::load($id);

$workflow->addActivity(MyActivityC::class);

[im-Clement]

That is very clever.

Thank you. I will let you know how is it going on tests.

[zebaroni]

Any updates on this feature?