Option for blocking parallel workflow execution

Feature Requests
1

When using cron trigger with a short interval it can happen that a workflow is running in parallel. When the workflow is chewing through some data the second instance would do the same and this builds up.

For the time being I use a blocker like the one below. But I think this is something that can be handled in an option for the workflow even better.

    {
  "nodes": [
    {
      "parameters": {},
      "name": "Start",
      "type": "n8n-nodes-base.start",
      "typeVersion": 1,
      "position": [
        260,
        -390
      ]
    },
    {
      "parameters": {
        "triggerTimes": {
          "item": [
            {
              "mode": "everyMinute"
            }
          ]
        }
      },
      "name": "Cron",
      "type": "n8n-nodes-base.cron",
      "typeVersion": 1,
      "position": [
        260,
        -140
      ]
    },
    {
      "parameters": {
        "conditions": {
          "boolean": [],
          "string": [],
          "number": [
            {
              "value1": "= {{$json[\"runningWorkflows\"]}}",
              "operation": "larger",
              "value2": 1
            }
          ]
        }
      },
      "name": "IF already running",
      "type": "n8n-nodes-base.if",
      "typeVersion": 1,
      "position": [
        880,
        -270
      ]
    },
    {
      "parameters": {},
      "name": "NoOp",
      "type": "n8n-nodes-base.noOp",
      "typeVersion": 1,
      "position": [
        1070,
        -290
      ]
    },
    {
      "parameters": {
        "functionCode": "const returnItems = [];\nvar runningWorkflows = 0;\n\nfor (const item of $node[\"Get current Executions\"].json[\"data\"]) {\n  if(item.workflowId == $workflow.id) {\n    runningWorkflows++;\n  }\n}\n\nreturnItems.push({json: {\"runningWorkflows\": runningWorkflows}});\n\nreturn returnItems;\n"
      },
      "position": [
        710,
        -270
      ],
      "name": "Get runningWorkflows",
      "type": "n8n-nodes-base.function",
      "typeVersion": 1
    },
    {
      "parameters": {
        "url": "={{$node[\"Init\"].parameter[\"values\"][\"string\"][0][\"value\"]}}/rest/executions-current",
        "allowUnauthorizedCerts": true,
        "jsonParameters": true,
        "options": {}
      },
      "position": [
        530,
        -270
      ],
      "name": "Get current Executions",
      "type": "n8n-nodes-base.httpRequest",
      "typeVersion": 1
    }
  ],
  "connections": {
    "Start": {
      "main": [
        [
          {
            "node": "Get current Executions",
            "type": "main",
            "index": 0
          }
        ]
      ]
    },
    "Cron": {
      "main": [
        [
          {
            "node": "Get current Executions",
            "type": "main",
            "index": 0
          }
        ]
      ]
    },
    "IF already running": {
      "main": [
        [
          {
            "node": "NoOp",
            "type": "main",
            "index": 0
          }
        ]
      ]
    },
    "Get runningWorkflows": {
      "main": [
        [
          {
            "node": "IF already running",
            "type": "main",
            "index": 0
          }
        ]
      ]
    },
    "Get current Executions": {
      "main": [
        [
          {
            "node": "Get runningWorkflows",
            "type": "main",
            "index": 0
          }
        ]
      ]
    }
  }
}
2

I would be really interested in this as well. I am using this for alerts management and i have racing conditions. For example:

  1. Worflow 1 executes and checks if alert with given hash has been created. It has not so it proceeds
  2. Second workflow is doing the same but it is faster
  3. Workflow 1 tried to create alert but it has been created already by another execution.

Please advise on how to avoid this. If there is a variable EXECUTIONS_PROCESS to control parallelism between workflows, we need the same to force n8n to wait on each execution before executing the others.

1 Like
3

It’s a mandatory feature to avoid on-field problems.

2 Likes
4

Yep, moving from Integromat to n8n and having to find work-arounds for this. We have two critical workflows that we must guarantee are not run twice for the same items.

It should be a workflow setting with an option to either save oncoming triggers in a queue or refuse execution.

2 Likes
5

I really need this feature to prevent parallel workflow executions. Especially for the schedule trigger node.

1 Like
6

FWIW, my ideal solution for this would probably be a boolean slider in the Workflow Settings that says something like “Prevent parallel executions” (tooltip: “Only allow a single instance of this workflow to run at a time”). Thanks for considering!