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Run Multiple Tasks in Parallel with Asynchronous Processing and Webhooks

https://n8nworkflows.xyz/workflows/run-multiple-tasks-in-parallel-with-asynchronous-processing-and-webhooks-8578

Run Multiple Tasks in Parallel with Asynchronous Processing and Webhooks

1. Workflow Overview

This workflow demonstrates a proof-of-concept implementation for running multiple asynchronous tasks in parallel using n8n. Its primary use case is to orchestrate long-running or delayed processes without blocking the main workflow execution, ideal for batch processing or parallel task management.

Logical Blocks:

  • 1.1 Entry & Trigger Block: Handles manual and external trigger inputs to start the workflow asynchronously.
  • 1.2 Asynchronous Task Execution Block: Launches multiple parallel sub-workflows without waiting for their completion.
  • 1.3 Wait & Webhook Reception Block: Uses Wait nodes configured with webhooks to pause execution until asynchronous tasks report back.
  • 1.4 Result Aggregation Block: Merges and summarizes results received from asynchronous tasks.

2. Block-by-Block Analysis

1.1 Entry & Trigger Block

Overview:
This block initiates the workflow either manually or via an external trigger and passes input parameters to downstream nodes.

Nodes Involved:

  • Start
  • Call Entry Point

Node Details:

  • Start

    • Type: Manual Trigger
    • Role: Entry point for manual execution.
    • Configuration: No parameters; simply triggers workflow on user command.
    • Connections: Output to "Call 1".
    • Edge Cases: None typical; manual trigger requires human initiation.

  • Call Entry Point

    • Type: Execute Workflow Trigger
    • Role: Receives input parameters for asynchronous calls, including wait time and a webhook URL.
    • Configuration: Defines two expected inputs: a number wait and a string webhook.
    • Key Expressions: Passes these inputs downstream using expressions, e.g., {{ $('Call Entry Point').item.json.wait }}.
    • Connections: Outputs to "Wait Seconds".
    • Edge Cases: Input validation failure if wait or webhook is missing or invalid.

1.2 Asynchronous Task Execution Block

Overview:
This block executes two parallel asynchronous workflows ("Call 1" and "Call 2") without waiting for their completion, enabling concurrent long-running task execution.

Nodes Involved:

  • Call 1
  • Call 2

Node Details:

  • Call 1

    • Type: Execute Workflow
    • Role: Starts sub-workflow asynchronously with no waiting (waitForSubWorkflow=false).
    • Configuration:
      • Calls the same workflow by ID (self-reference) to simulate parallel tasks.
      • Passes parameters: wait=5 seconds and a webhook URL constructed using {{$execution.resumeUrl}}/call1.
    • Connections: Output to "Call 2".
    • Edge Cases:
      • Must ensure sub-workflow ID is correct and that asynchronous execution is supported.
      • Misconfigured webhook URLs could cause resume failures.

  • Call 2

    • Type: Execute Workflow
    • Role: Similar to "Call 1" but with different parameters to simulate another parallel task.
    • Configuration:
      • wait=3 seconds, webhook URL: {{$execution.resumeUrl}}/call2.
    • Connections: Outputs to "Wait for Webhook 1" and "Wait for Webhook 2".
    • Edge Cases: Same as "Call 1".

1.3 Wait & Webhook Reception Block

Overview:
This block uses wait nodes configured to resume on webhooks to asynchronously pause the workflow until each external sub-task signals completion.

Nodes Involved:

  • Wait Seconds
  • Wait for Webhook 1
  • Wait for Webhook 2
  • Request Webhook
  • Wait 1 Second

Node Details:

  • Wait Seconds

    • Type: Wait
    • Role: Delays execution for a dynamically defined amount of time (wait parameter).
    • Configuration: Wait duration set via expression referencing Call Entry Point's input wait.
    • WebhookId: Defined to allow resuming if needed.
    • Connections: Output to "Request Webhook".
    • Edge Cases: Invalid or zero wait values may cause immediate continuation.

  • Request Webhook

    • Type: HTTP Request
    • Role: Sends a POST request to the webhook URL passed in inputs, reporting back results.
    • Configuration:
      • Sends a JSON body with a result field, calculated as wait * 2.
      • Continues workflow on error (onError: continueErrorOutput).
    • Connections:
      • On success, no further action.
      • On failure, triggers "Wait 1 Second" node to retry or delay.
    • Edge Cases: Possible HTTP errors, webhook URL unreachable, timeouts.

  • Wait 1 Second

    • Type: Wait
    • Role: Pauses for 1 second, likely used for retry delay after failed HTTP requests.
    • Connections: Output loops back to "Request Webhook".
    • Edge Cases: Infinite loop risk if "Request Webhook" keeps failing.

  • Wait for Webhook 1

    • Type: Wait (Webhook Resume)
    • Role: Pauses workflow until webhook callback at suffix /call1 is received.
    • Configuration:
      • Resume on webhook with suffix "call1".
      • Limits wait time (minutes).
    • Connections: Output to "Merge" node.
    • Edge Cases: If webhook never received, workflow may timeout or stall.

  • Wait for Webhook 2

    • Type: Wait (Webhook Resume)
    • Role: Same as above but listens on webhook suffix "call2".
    • Connections: Output to "Merge".
    • Edge Cases: Same as "Wait for Webhook 1".

1.4 Result Aggregation Block

Overview:
This block merges the results returned from the asynchronous tasks and performs a summary aggregation.

Nodes Involved:

  • Merge
  • Sum

Node Details:

  • Merge

    • Type: Merge
    • Role: Combines incoming data streams from "Wait for Webhook 1" and "Wait for Webhook 2".
    • Configuration: Default merge mode (likely "Wait for All").
    • Connections: Output to "Sum".
    • Edge Cases: Missing inputs from either wait node may cause indefinite waiting.

  • Sum

    • Type: Summarize
    • Role: Aggregates numeric results by summing the body.result fields from merged inputs.
    • Configuration: Sum aggregation on field body.result.
    • Connections: Terminal node with no outputs.
    • Edge Cases: Non-numeric or missing result fields may cause errors or incorrect sums.

3. Summary Table

Node Name Node Type Functional Role Input Node(s) Output Node(s) Sticky Note
Start Manual Trigger Manual workflow trigger — Call 1
Call Entry Point Execute Workflow Trigger Receives external inputs for async tasks — Wait Seconds
Wait Seconds Wait Waits dynamically based on input Call Entry Point Request Webhook
Request Webhook HTTP Request Sends callback to provided webhook URL Wait Seconds — (success), Wait 1 Second (error)
Wait 1 Second Wait Delay before retrying webhook request Request Webhook (error) Request Webhook
Call 1 Execute Workflow Starts async sub-workflow #1 Start Call 2
Call 2 Execute Workflow Starts async sub-workflow #2 Call 1 Wait for Webhook 1, Wait for Webhook 2
Wait for Webhook 1 Wait (Webhook Resume) Waits for async task #1 webhook callback Call 2 Merge
Wait for Webhook 2 Wait (Webhook Resume) Waits for async task #2 webhook callback Call 2 Merge
Merge Merge Combines webhook results Wait for Webhook 1, Wait for Webhook 2 Sum
Sum Summarize Aggregates results by summing field Merge —
Sticky Note Sticky Note Documentation and instructions — — ## n8n Asynchronous Workflow with Wait Node POC This template contains a two-part workflow designed to demonstrate a proof-of-concept for asynchronous and parallel execution of tasks in n8n. The blog post link: https://n8nplaybook.com/post/2025/09/asynchronous-n8n-workflows-parallel-processing-poc/

4. Reproducing the Workflow from Scratch

  1. Create Manual Trigger Node:

    • Name: Start
    • Type: Manual Trigger
    • No parameters.
    • Position it at the left/start of your canvas.

  2. Add Execute Workflow Trigger Node:

    • Name: Call Entry Point
    • Type: Execute Workflow Trigger
    • Configure inputs schema with two parameters:
      • wait (Number)
      • webhook (String)
    • Position below Start.
    • Connect output of Start to input of this node.

  3. Add Wait Node (Dynamic):

    • Name: Wait Seconds
    • Type: Wait
    • Set the amount to an expression: {{$node["Call Entry Point"].json["wait"]}}
    • Assign a unique webhook ID (auto-generated by n8n).
    • Connect from Call Entry Point.

  4. Add HTTP Request Node:

    • Name: Request Webhook
    • Type: HTTP Request
    • Method: POST
    • URL: Expression: {{$node["Call Entry Point"].json["webhook"]}}
    • Body parameters JSON:
      • Parameter name: result
      • Value expression: {{$node["Call Entry Point"].json["wait"] * 2}}
    • Set Continue on Fail to true.
    • Connect from Wait Seconds.

  5. Add Wait Node (1 second delay):

    • Name: Wait 1 Second
    • Type: Wait
    • Amount: 1 (second)
    • Connect error output of Request Webhook to this node.
    • Connect output of Wait 1 Second back to Request Webhook for retries.

  6. Add Execute Workflow Node (Call 1):

    • Name: Call 1
    • Type: Execute Workflow
    • Select the same workflow ID to call itself asynchronously.
    • Set Wait for Sub-Workflow to false.
    • Inputs:
      • wait: 5
      • webhook: Expression: {{$execution.resumeUrl}}/call1
    • Connect from Start.

  7. Add Execute Workflow Node (Call 2):

    • Name: Call 2
    • Type: Execute Workflow
    • Same configuration as Call 1 but:
      • wait: 3
      • webhook: Expression: {{$execution.resumeUrl}}/call2
    • Connect output of Call 1 to input.

  8. Add Wait Nodes for Webhook Resume:

    • Name: Wait for Webhook 1
      • Type: Wait
      • Configure to resume on webhook with suffix call1.
      • Limit wait time.
      • Connect output of Call 2.
    • Name: Wait for Webhook 2
      • Same as above but suffix call2.
      • Connect output of Call 2.

  9. Add Merge Node:

    • Name: Merge
    • Type: Merge
    • No special parameters.
    • Connect outputs of Wait for Webhook 1 and Wait for Webhook 2.

  10. Add Summarize Node:

    • Name: Sum
    • Type: Summarize
    • Configure to sum the field body.result.
    • Connect from Merge.

  11. Add Sticky Note:

    • Content with workflow purpose, usage, and link to blog post (optional).

  12. Ensure all nodes are positioned logically and connected as per above.

  13. Credentials:

    • No special credentials required for this workflow.
    • If HTTP requests go to external endpoints requiring auth, configure accordingly.

5. General Notes & Resources

Note Content Context or Link
This workflow is a demonstration of asynchronous and parallel task execution using n8n’s Wait node and webhook resume pattern, suitable for batch processing scenarios. Workflow purpose
For detailed explanation and concepts behind this proof-of-concept, see the blog post: https://n8nplaybook.com/post/2025/09/asynchronous-n8n-workflows-parallel-processing-poc/ https://n8nplaybook.com/post/2025/09/asynchronous-n8n-workflows-parallel-processing-poc/
The workflow calls itself asynchronously to simulate parallel tasks; make sure to import and link workflows correctly when deploying in your environment. Setup instructions in sticky note

Disclaimer: The provided text is derived exclusively from an n8n automated workflow. It complies strictly with current content policies and includes only legal, public data.

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