How to write my own engine? Docs?

[rvetere]

Hi i found the repository "https://github.com/shoreditch-ops/artillery-engine-kinesis" which seems to solve exactly what i need - writing my own engine.. I did it already by forking the whole artillery repository and got it running, but it feels as a total overkill to fork the whole thing just to introduce a new engine.

But when i see code like this:

      let runnerEngines = _.map(
      Object.assign({}, Engines, runnableScript.config.engines),
      function loadEngine(engineConfig, engineName) {
        let moduleName = 'artillery-engine-' + engineName;
        try {
          if (Engines[engineName]) {
            moduleName = './engine_' + engineName;
          }
          let Engine = require(moduleName);
     ....

-> the runner code is hardcoded looking into his own folder relatively with all the entries of "Engines"... i don't see how this should be dynamically able to pick up some new written engines at all oO

So... how should this work?

[hassy]

hi @rvetere, the way to get it going locally is:

1. Clone Artillery, run npm install in the directory, this will let you run a local copy of Artillery with ./bin/artillery
2. In the directory where your custom engine code is (let's say artillery-engine-rvetere) run npm link
3. Back inside Artillery's source dir run npm link artillery-engine-rvetere (more info on npm link)

This will allow that copy of Artillery to find and load your custom engine. It's important that you set the engine field of your scenario:

config:
  target: "some.target"
scenarios:
  - name: "Custom engine scenario"
    engine: "rvetere"
    flow:
     - do: something
     - do: something else

[kraenhansen]

Another way to do this is to create a package that has a dependency on both artillery and your custom engine (could be installed from ./artillery-engine-custom), this way artillery core will be able to require in your custom engine correctly.

In your root project folder:

my-script.yml

An artillery script using your custom engine.

package.json

{
  "name": "my-load-tests",
  "version": "0.1.0",
  "scripts": {
    "test": "artillery run ./my-script.yml"
  },
  "dependencies": {
    "artillery": "^1.6.0-27",
    "artillery-engine-realm": "file:artillery-engine-custom"
  }
}

A directory called artillery-engine-custom

This should be a module named "artillery-engine-custom" which main script should export an engine.

[dtrunk90]

Both ways don't work for me:

> artillery run "test.yml"

Started phase 0 (Test Phase), duration: 10s @ 17:16:19(+0200) 2021-05-03
  . /usr/local/lib/node_modules/artillery/core/lib/runner.js:390
          return engine.createScenario(scenarioSpec, runState.scenarioEvents);
                        ^

TypeError: Cannot read property 'createScenario' of undefined
    at /usr/local/lib/node_modules/artillery/core/lib/runner.js:390:25
    at arrayMap (/usr/local/lib/node_modules/artillery/node_modules/lodash/lodash.js:653:23)
    at Function.map (/usr/local/lib/node_modules/artillery/node_modules/lodash/lodash.js:9622:14)
    at runScenario (/usr/local/lib/node_modules/artillery/core/lib/runner.js:385:36)
    at EventEmitter.<anonymous> (/usr/local/lib/node_modules/artillery/core/lib/runner.js:274:7)
    at EventEmitter.emit (events.js:315:20)
    at UniformProcess.<anonymous> (/usr/local/lib/node_modules/artillery/core/lib/phases.js:182:10)
    at UniformProcess.emit (events.js:315:20)
    at /usr/local/lib/node_modules/artillery/node_modules/arrivals/lib/index.js:47:10
    at NanoTimer.setInterval (/usr/local/lib/node_modules/artillery/node_modules/arrivals/node_modules/nanotimer/lib/nanotimer.js:220:5)

[hassy]

Does your engine define a createScenario function @dtrunk90?

[dtrunk90]

@hassy the engine itself is undefined, not the createScenario function.

[hassy]

ah yes, sorry! does Artillery print a warning that it can't load the engine when you run the test? a minimal reproducible example would be great.

[dtrunk90]

https://github.com/dtrunk90/artillery-engine-rsocket

With a running Spring Boot RSocket Application:

config:
  target: "localhost"
  engine: "rsocket"
  phases:
    - duration: 10
      arrivalRate: 1
      name: "Test Phase"

scenarios:
  - name: "Test Scenario"
    flow:
      - emit:
          route: "hello"
          operation: "stream"
          data:
            - "world"

and artillery doesn't print any warning unfortunately.

[hassy]

Ah sorry, the engine needs to be specified in config.engines like this:

config:
  target: localhost
  phases:
    - duration: 10
      arrivalRate: 1
      name: "Test Phase"
  engines:
    rsocket: {}

I was able to run your script + engine after adding that bit to the config. Let me know if you run into any other issues!

[dtrunk90]

At least it runs. It doesn't send any requests but that could be a problem of my custom engine implementation.

[hassy]

Great! Feel free to create a new RSocket-specific issue if you need pointers @dtrunk90

[dtrunk90]

Thank you.