Prevent Concurrent Workflow Runs Using Redis

This n8n workflow demonstrates a robust method to prevent multiple instances of a workflow from running simultaneously, utilizing Redis as a locking mechanism. This is crucial for workflows that perform operations which should not be duplicated or interleaved, such as data synchronization, report generation, or resource provisioning.

What it does

This workflow acts as a wrapper or a sub-workflow that ensures only one execution of a critical process (represented by a "Child Workflow" in this example) can proceed at a time. It leverages Redis to manage a lock, preventing race conditions and ensuring data integrity.

1. Trigger: The workflow can be initiated either manually or by another workflow.
2. Set Workflow ID: It first prepares a unique workflow ID to be used as the lock key in Redis.
3. Acquire Lock: It attempts to acquire a lock in Redis using the prepared ID.
   • If the lock is successfully acquired, it proceeds to execute the "Child Workflow".
   • If the lock is already held by another instance, it stops the current execution with an error, preventing concurrency.
4. Execute Child Workflow: If the lock is obtained, it calls a "Child Workflow" (placeholder in this example) that contains the actual critical logic.
5. Release Lock (On Success): After the "Child Workflow" completes successfully, the lock in Redis is released, allowing future executions to proceed.
6. Release Lock (On Error): If any error occurs during the execution of the "Child Workflow", the lock is also released to prevent a permanent deadlock, and the workflow stops with an error.
7. Wait for Lock Release (Optional): An optional "Wait" node is included to demonstrate a scenario where the workflow might wait for a short period before retrying to acquire the lock, though in this specific setup, it immediately errors out if the lock is not available.

Prerequisites/Requirements

• n8n Instance: A running n8n instance.
• Redis Server: Access to a Redis server.
• Redis Credential: A configured Redis credential in your n8n instance.
• Child Workflow: A separate n8n workflow that contains the critical logic you want to protect from concurrent runs. This workflow should be configured to be executable by another workflow.

Setup/Usage

1. Import the Workflow: Import the provided JSON into your n8n instance.
2. Configure Redis Credential:
   • Ensure you have a Redis credential set up in n8n. The "Redis" node in the workflow will require this.
3. Configure Workflow ID:
   • The "Edit Fields" node (named "Set Workflow ID") sets the workflowId which is used as the Redis key for the lock. Customize this value to be unique for the critical workflow you are protecting.
4. Link Child Workflow:
   • The "Execute Workflow" node (named "Execute Child Workflow") is a placeholder. You need to configure this node to call your actual critical workflow. Select the workflow you want to protect from concurrent runs.
5. Activate the Workflow: Once configured, activate the workflow.

When this workflow is triggered, it will ensure that only one instance of your "Child Workflow" runs at any given time. If a second instance attempts to run while the first is active, it will be stopped with an error.