Websocket requests are not being executed concurrently

[luizbafilho]

When running the script below with --vus 5, instead of getting the connected message 5 times, one for each VU, we get the message just once.

import ws from "k6/ws";
import { check } from "k6";

export default function () {
    var url = "ws://echo.websocket.org";

    var response = ws.connect(url, {}, function (socket) {
        socket.on('open', function open() {
            console.log(`VU ${__VU} ==> connected`);
            socket.ping();
        });

        socket.on('ping', function () {
            console.log("PING!");
        });

        socket.on('pong', function () {
            console.log("PONG!");
        });

        socket.on('close', function close() {
            console.log('disconnected');
        });

        socket.on('error', function (e) {
            if (e.error() != "websocket: close sent") {
                console.log('An unexpected error occured: ', e.error());
            }
        });

        socket.setTimeout(function () {
            console.log('1 seconds passed, closing the socket');
            socket.close();
        }, 1000);
    });

    check(response, { "status is 101": (r) => r && r.status === 101 });
};

Running with 5 VUs and 1 iteration.

$ k6 run --vus 5 samples/websocket.js

          /\      |‾‾|  /‾‾/  /‾/
     /\  /  \     |  |_/  /  / /
    /  \/    \    |      |  /  ‾‾\
   /          \   |  |‾\  \ | (_) |
  / __________ \  |__|  \__\ \___/ .io

  execution: local
     output: -
     script: samples/websocket.js

    duration: -,  iterations: 1
         vus: 5, max: 5

INFO[0001] VU 5 ==> connected
INFO[0001] PONG!
INFO[0002] 1 seconds passed, closing the socket
INFO[0002] disconnected
    done [==========================================================] 1 / 1

    ✓ status is 101

    checks................: 100.00% ✓ 1   ✗ 0
    data_received.........: 204 B   126 B/s
    data_sent.............: 204 B   126 B/s
    iteration_duration....: avg=1.6s       min=1.6s       med=1.6s       max=1.6s       p(90)=1.6s       p(95)=1.6s
    iterations............: 1       0.622171/s
    vus...................: 5       min=5 max=5
    vus_max...............: 5       min=5 max=5
    ws_connecting.........: avg=605.84ms   min=605.84ms   med=605.84ms   max=605.84ms   p(90)=605.84ms   p(95)=605.84ms
    ws_ping...............: avg=111.046319 min=111.046319 med=111.046319 max=111.046319 p(90)=111.046319 p(95)=111.046319
    ws_session_duration...: avg=1.6s       min=1.6s       med=1.6s       max=1.6s       p(90)=1.6s       p(95)=1.6s
    ws_sessions...........: 1       0.622171/s

Running with 5 VUs with 5 iterations.

k6 run --vus 5 -i 5  samples/websocket.js

          /\      |‾‾|  /‾‾/  /‾/
     /\  /  \     |  |_/  /  / /
    /  \/    \    |      |  /  ‾‾\
   /          \   |  |‾\  \ | (_) |
  / __________ \  |__|  \__\ \___/ .io

  execution: local
     output: -
     script: samples/websocket.js

    duration: -,  iterations: 5
         vus: 5, max: 5

INFO[0001] VU 4 ==> connected
INFO[0001] VU 2 ==> connected
INFO[0001] VU 3 ==> connected
INFO[0001] VU 5 ==> connected
INFO[0001] VU 1 ==> connected
INFO[0001] PONG!
INFO[0001] PONG!
INFO[0001] PONG!
INFO[0001] PONG!
INFO[0001] PONG!
INFO[0002] 1 seconds passed, closing the socket
INFO[0002] disconnected
INFO[0002] 1 seconds passed, closing the socket
INFO[0002] disconnected
INFO[0002] 1 seconds passed, closing the socket
INFO[0002] 1 seconds passed, closing the socket
INFO[0002] disconnected
INFO[0002] disconnected
INFO[0002] 1 seconds passed, closing the socket
INFO[0002] disconnected
    done [==========================================================] 5 / 5

    ✓ status is 101

    checks................: 100.00% ✓ 5   ✗ 0
    data_received.........: 1.0 kB  711 B/s
    data_sent.............: 1.0 kB  711 B/s
    iteration_duration....: avg=1.43s      min=1.42s      med=1.43s      max=1.43s     p(90)=1.43s      p(95)=1.43s
    iterations............: 5       3.489127/s
    vus...................: 5       min=5 max=5
    vus_max...............: 5       min=5 max=5
    ws_connecting.........: avg=425.62ms   min=415.82ms   med=427.66ms   max=429.02ms  p(90)=428.79ms   p(95)=428.9ms
    ws_ping...............: avg=116.312543 min=106.473666 med=118.354512 max=119.56554 p(90)=119.310812 p(95)=119.438176
    ws_session_duration...: avg=1.42s      min=1.42s      med=1.43s      max=1.43s     p(90)=1.43s      p(95)=1.43s
    ws_sessions...........: 5       3.489127/s

[luizbafilho]

This is the expected behavior, it doesn't matter the number of VUs if the number of iterations is specified it will only run the specified number