This is documentation for the next version of K6. For the latest stable release, go to the latest version.
Execution context variables
In some cases, it’s really useful to have information about the script’s current test-execution state. For example, you might want to
- Have different VUs run different test logic
- Use different data for each VU and iteration
- Figure out the stage that a test is in
To solve these issues, you can use execution context variables.
k6/execution
The k6/execution module exposes details about the current execution state, such as the name of the currently executed scenario, how many VUs are currently active, and more. The module provides test-execution information via three properties:
Property | Meta-information and execution details about |
---|---|
instance | The current running k6 instance |
scenario | The current running scenario |
vu | The current VU and iteration |
Example: log all context variables
If you want to experiment with what each context variable looks like as a test runs, you can copy this template literal into one of your test scripts.
Note that this omits the abort
variable, since that function would abort the test.
import exec from 'k6/execution';
export default function () {
console.log(`Execution context
Instance info
-------------
Vus active: ${exec.instance.vusActive}
Iterations completed: ${exec.instance.iterationsCompleted}
Iterations interrupted: ${exec.instance.iterationsInterrupted}
Iterations completed: ${exec.instance.iterationsCompleted}
Iterations active: ${exec.instance.vusActive}
Initialized vus: ${exec.instance.vusInitialized}
Time passed from start of run(ms): ${exec.instance.currentTestRunDuration}
Scenario info
-------------
Name of the running scenario: ${exec.scenario.name}
Executor type: ${exec.scenario.executor}
Scenario start timestamp: ${exec.scenario.startTime}
Percenatage complete: ${exec.scenario.progress}
Iteration in instance: ${exec.scenario.iterationInInstance}
Iteration in test: ${exec.scenario.iterationInTest}
Test info
---------
All test options: ${exec.test.options}
VU info
-------
Iteration id: ${exec.vu.iterationInInstance}
Iteration in scenario: ${exec.vu.iterationInScenario}
VU ID in instance: ${exec.vu.idInInstance}
VU ID in test: ${exec.vu.idInTest}
VU tags: ${exec.vu.tags}`);
}
For detailed reference, refer to the k6/execution module.
Additional examples
Note
k6 v0.34.0 introduced the k6/execution module. If you are using a version of k6 that doesn’t have this module, use__VU
and__ITER
.
__VU
and __ITER
are both global variables with execution-context information that k6 makes available to the test script.
__ITER
: A numeric counter with the current iteration number for a specific VU. Zero-based.__VU
: Current VU number in use. k6 assigns the value incrementally for each new VU instance, starting from one. The variable is 0 when executing the setup and teardown functions.
Running in k6 Cloud
When you run tests in Grafana Cloud k6, the __VU value is per server/load generator.
Examples
import http from 'k6/http';
import { sleep } from 'k6';
export default function () {
http.get('http://test.k6.io');
console.log(`VU: ${__VU} - ITER: ${__ITER}`);
sleep(1);
}
You can use execution-context variables to configure different test behaviors and parameterizations. A typical use case is a load test that simulates different users performing a login flow.
import http from 'k6/http';
import { sleep } from 'k6';
export default function () {
const email = `user+${__VU}@mail.com`;
const payload = JSON.stringify({ email: email, password: 'test' });
const params = { headers: { 'Content-Type': 'application/json' } };
http.post('http://test.k6.io/login', payload, params);
console.log(email);
// .. continue the user flow
sleep(1);
}
Grafana Cloud k6 context variables
Grafana Cloud k6 injects additional context variables into a running cloud test. These variables provide information about the server (K6_CLOUDRUN_INSTANCE_ID
), load zone (K6_CLOUDRUN_LOAD_ZONE
),instance ID (K6_CLOUDRUN_INSTANCE_ID
), and cloud distribution (K6_CLOUDRUN_DISTRIBUTION
).
Refer to Cloud execution context variables for more details.