Main thread in SlackApiLambdaHandler is completing before App's EventsDispatcher thread finishes in AWS Lambda. Am I missing something?

[Flyer4109]

I have an App with a WorkflowStep that I pass into the constructor of a class that extends SlackApiLambdaHandler. I have tested the App locally so I know that app works. I have deployed the app to AWS Lambda but whenever the function is invoked the 'workstep execute' doesn't finish. I think this happens because the workflow execute step is queued and executed on a separate thread in EventsDispatcherImpl so the main thread finishes first.

I feel like I am missing something. Can someone please advice me on what to do next?

Thanks in advance!

Reproducible in:

The Slack SDK version

[INFO] +- com.slack.api:bolt:jar:1.24.0:compile
[INFO] |  +- com.slack.api:slack-api-model:jar:1.24.0:compile
[INFO] |  +- com.slack.api:slack-api-client:jar:1.24.0:compile
[INFO] |  \- com.slack.api:slack-app-backend:jar:1.24.0:compile
[INFO] +- com.slack.api:bolt-jetty:jar:1.24.0:compile
[INFO] |  +- com.slack.api:bolt-servlet:jar:1.24.0:compile
[INFO] +- com.slack.api:bolt-aws-lambda:jar:1.24.0:compile

Java Runtime version

openjdk version "11.0.11" 2021-04-20
OpenJDK Runtime Environment AdoptOpenJDK-11.0.11+9 (build 11.0.11+9)
OpenJDK 64-Bit Server VM AdoptOpenJDK-11.0.11+9 (build 11.0.11+9, mixed mode)

OS info

Steps to reproduce:

Expected result:

Actual result:

Requirements

[seratch]

Hi @Flyer4109, thanks for writing in.

The reason why the "workflow execute" event handling is executed asynchronously in a different thread is mentioned in the code comment as below:

As the workflows.stepCompleted is really slow (it always takes 3+ seconds), this middleware automatically runs the API call asynchronously. If you want to use your own mechanism to handle this, use your own middleware or add your primitive listener by App#worflowStepExecute() method. https://github.com/slackapi/java-slack-sdk/blob/v1.24.0/bolt/src/main/java/com/slack/api/bolt/middleware/builtin/WorkflowStep.java#L86-L100

Due to the above workflow platform API performance issue, running your app on container services such as ECS would be much easier. That being said, there is still a solution. If you would like to run the workflow step on AWS Lambda, a solution that I suggest would be:

• Set WorkflowStep#executeAutoAcknowledgement to false (default: true)
• Enqueue the execute event in SQS or whatever similar and then run the logic asynchronously (in a different AWS Lambda execution)

I hope this helps.

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