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Legion is a load testing tool for HTTP servers and other kinds of software. It consists of two major components: legion-metrics, which collects and merges performance metrics from various sources; and legion-io, a Promise-based library that makes it quick and easy to describe a testcase.

To get started with Legion, and find lots of end-user documentation, start by cloning the starter kit.

A legion testcase is chained together from pieces, in much the same way that we use promises:

const L = require('legion');
const fetch = require('legion-io-fetch');
const delay = require('legion-io-delay');

const my_testcase = Io.of()
  .chain(fetch.text('http://www.example.com/'))
  .chain(delay(10))
  .chain(fetch.text('http://www.example.com/page1.html'))
  .chain(delay(10))
  .chain(fetch.text('http://www.example.com/page2.html'));

L.create()
 .withTestcase(my_testcase)
 .main();

And then executed from the command line (in this case, with 50 concurrent users):

node testcase.js -n 50

Visit the wiki for more information.

Command Line Options

When you run a Legion script using the main() method, you automatically get a number of CLI options:

--control-server

Self-host a control server inside this instance. You must also use the --control-endpoint flag to direct any running tests to update their command and control data from here.

--control-endpoint [url]

Retrieve command and contol information from a control server at the given URL.

--control-interval [integer]

Interval between updating command and control data from the control endpoint, in seconds.

--capture-server

Self-host a metrics-capture server inside this instance. You must also use the --capture-endpoint flag to direct any running tests to send their metrics data here.

--capture-endpoint [url]

Send metrics data to a metrics capture server at the given URL.

--capture-interval [integer]

Interval between flushing metrics data to the metrics capture endpoint, in seconds.

--project-key [string]

An arbitrary value used to identify this project or testing campaign. All Legion instances that are participating in the same project or testing campaign should use the same project-key. This allows metrics and control data for different projects to be kept separate.

--self-hosted

Automatically sets --control-server, --control-endpoint, --capture-server, and --capture-endpoint to sensible values for a self-contained, self-hosted, single-machine test run.

--users

Sets the number of concurrent users. By default, this will be 1.

API

const L = require('legion');

L.create()

Create a new Legion load test.

L.prototype

Prototype of all Legion load test objects.

L.prototype.using(module : object)

Imports a legion module into the load test.

L.prototype.withBeforeTestAction(f : function)

Adds an action to run before starting the load test. If you have multiple Legion instances running in parallel, this action will run once on each instance.

Returns: A load test object incorporating the given before-test action.

L.prototype.withAfterTestAction(f : function)

Adds an action to run after finishing the load test. If you have multiple Legion instances running in parallel, this action will run once on each instance.

Returns: A load test object incorporating the given after-test action.

L.prototype.withGlobalService(f : function)

Adds an action to set up a service that will be available to all users. Any such services will appear in the services field of the state object.

  • f - a function taking a services object and returning a (possibly modified) services object.

Returns: A load test object incorporating the given global service.

Example:

L.create()
 .withGlobalService(services => {
       services.myExampleService = { foo: 'bar' };
       return services;
     })
     .withTestcase(L.get().chain(state => {
       console.log(state.services.foo); //prints 'bar'
     });

L.prototype.withUserService(f : function)

Adds an action to set up a service so that a unique instance will be available to each virtual user. Any such services will appear in the services field of the state object.

Returns: A load test object incorporating the given user service.

Unlike the withGlobalService() method, the setup function that you supply to this method will be called once for each virtual user.

L.prototype.withMetricsTarget(target : object)

Supply a custom MetricsTarget to be used for this load test. This setting can be overridden from the command line.

Returns: A load test object that will use the given MetricsTarget to collect test metrics.

L.prototype.withController(target : object)

Supply a controller client object to be used for this load test. This setting can be overridden from the command line.

Returns: A load test object that will use the given controller client to orchestrate the load test.

L.prototype.withProjectKey(project_key : string)

Supply a project_key to be used for this load test. This setting can be overridden from the command line. The project_key is primarily used to uniquely identify a test run on both the controller and when capturing test metrics.

Returns: A load test object that will use the given project_key.

L.prototype.withTestcase(tc : function or object)

Supply a testcase to execute during this load test. A testcase is usually an Io object which wraps one or more functions that describe what the testcase should do. The simplest testcase is just one function that returns an ES6 Promise.

To chain multiple functions together, begin the chain with L.of():

L.create().withTestcase(
  L.of()
   .chain(() => Promise.resolve('operation one'))
   .chain(() => Promise.resolve('operation two'))
   .chain(() => Promise.resolve('operation three')))

L.prototype.run(n : number)

Run a load test.

  • n - the number of users to start

Note: consider using the main() method instead.

L.prototype.main()

Run a load test using command-line options. For example:

L.create()
 .withTestcase(L.of('simplest possible testcase'))
     .main();

L.of(value : any)

Constructs the simplest possible Io action, returning a fixed value.

L.get()

An Io action that gets the embedded state and passes it to the next action.

L.projectKey()

An Io action that gets the project key and passes it to the next action.

L.controller()

An Io action that gets the controller client and passes it to the next action. Usually you use L.getControlData() or L.getCounters() instead.

L.getControlData()

An Io action that gets the control data for this load test. Control data is provided by a control server and can be used to synchronize the behavior of several legion instances in real time.

L.getCounters(counter_key:string, n:number)

An Io action that allocates some counters that will be unique for this virtual user. Counters are small numbers (starting from zero) that are provided from a single control server and guaranteed to be unique for each call, project_key, and controller server.

L.getUserUniqueId()

An Io action that gets the Version 4 UUID for this virtual user.