Running a flow triggered via HTTP concurrently

General
1

I am sorry if that has been answered somewhere else already, I haven't found exactly what I need via search.

Let's say I'm building a flow that starts with an http-in node so that the flow can be triggered via an HTTP endpoint.

Inside of the flow, there is some data processing such as reading from/writing to a database, sending notifications, etc.

Currently, with just http-in -> json -> delay (for testing purposes) -> http-out, if I trigger the flow in multiple browser tables, they all run sequentially so that the second invocation waits until the first one finishes.

I understand that most likely this is due to how Node.js works, but is there any way to have parallel instances of the same flow?

To explain better the usecase: a flow for me is a template for a pipeline which can be run by multiple users at the same time, and it would be unfortunate to run all instances one at a time.

Thanks!

2

Do you mean it is waiting for the http out to complete before accepting the next http in? That should not happen.

3

This is not true.

GIF demonstrating async (non sequential) operation

WindowsTerminal_QSZVo8nuxo

demo flow

[{"id":"10db3e6940831566","type":"http in","z":"65608a30f8a8cec4","name":"","url":"/test","method":"get","upload":false,"swaggerDoc":"","x":470,"y":600,"wires":[["fe98d449ecd63dc1","5150a9b9cf5c5f16"]]},{"id":"fe98d449ecd63dc1","type":"function","z":"65608a30f8a8cec4","name":"function 4","func":"msg.payload = \"You specified a delay of \" + msg.req.query.delay + \"ms\"\n\nmsg.delay = msg.req.query.delay\n\nreturn msg;","outputs":1,"timeout":0,"noerr":0,"initialize":"","finalize":"","libs":[],"x":620,"y":600,"wires":[["b680ee84852ef304"]]},{"id":"cab6ead2adc71b78","type":"http response","z":"65608a30f8a8cec4","name":"","statusCode":"","headers":{},"x":930,"y":600,"wires":[]},{"id":"b680ee84852ef304","type":"delay","z":"65608a30f8a8cec4","name":"","pauseType":"delayv","timeout":"1","timeoutUnits":"seconds","rate":"1","nbRateUnits":"1","rateUnits":"second","randomFirst":"1","randomLast":"5","randomUnits":"seconds","drop":false,"allowrate":false,"outputs":1,"x":770,"y":600,"wires":[["cab6ead2adc71b78"]]},{"id":"5150a9b9cf5c5f16","type":"debug","z":"65608a30f8a8cec4","name":"debug 197","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"true","targetType":"full","statusVal":"","statusType":"auto","x":600,"y":680,"wires":[]}]
4 
[
    {
        "id": "106100fc7cbdc224",
        "type": "http in",
        "z": "ae2f93afd21df814",
        "name": "test-flow",
        "url": "test-flow",
        "method": "get",
        "upload": false,
        "swaggerDoc": "",
        "x": 100,
        "y": 360,
        "wires": [
            [
                "7f2b789a8ae3ed50"
            ]
        ]
    },
    {
        "id": "56cfb5bbb2f7b604",
        "type": "http response",
        "z": "ae2f93afd21df814",
        "name": "",
        "statusCode": "",
        "headers": {},
        "x": 790,
        "y": 340,
        "wires": []
    },
    {
        "id": "7f2b789a8ae3ed50",
        "type": "json",
        "z": "ae2f93afd21df814",
        "name": "",
        "property": "req.query",
        "action": "",
        "pretty": false,
        "x": 350,
        "y": 360,
        "wires": [
            [
                "9e7cd1649a3338e3"
            ]
        ]
    },
    {
        "id": "9e7cd1649a3338e3",
        "type": "delay",
        "z": "ae2f93afd21df814",
        "name": "",
        "pauseType": "delay",
        "timeout": "5",
        "timeoutUnits": "seconds",
        "rate": "1",
        "nbRateUnits": "1",
        "rateUnits": "second",
        "randomFirst": "1",
        "randomLast": "5",
        "randomUnits": "seconds",
        "drop": false,
        "allowrate": false,
        "outputs": 1,
        "x": 560,
        "y": 360,
        "wires": [
            [
                "56cfb5bbb2f7b604"
            ]
        ]
    }
]

Here is mine. Maybe, I just created the flow in a stupid way, but my second tab does wait for the first one to complete with this setup.

5

Let me clarify (see the flow JSON above).

What happens is that if I have two tabs where I trigger /test-flow at the same time, the second one finishes in 10 seconds, not in 5-6 as if waiting for the first one to finish first.

The example suggested by @Steve-Mcl, however, works but I don't understand why mine doesn't now :slight_smile:

6

Try setting your delay node to a random time, then you may see that the second http request can finish before the first.

7

Yeah, that makes sense, but I still don't understand what happens in my simple example above.

If I deploy the flow and then trigger it in 3 tabs in a row, the last one will get a response in ~15 seconds. I do not expect exactly 5 seconds, this is all concurrent, I understand, but they seem to be running sequentially which makes me think (baed on the example above that works differently) that something is clearly wrong in my flow.

8

That maybe the browser executing each tab concurrently as they are calling same page. Try in different browsers and/or different devices.

9

Okay, this even sounds strange, but it's subjectively worse when the delay is fixed.
In your example, if I run 2 CURLs or browser tabs with delay=5000, one of them finishes in ~5s, but the second one takes about 10s. Is that expected?

10

It seems that you're right. Running 1 with curl and 1 in the browser works as expected. Weird. Looks like some browser special behavior. Thanks everyone for your help!

11

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