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Load Profiles and Ramping

How to set and control load profiles and user ramping for the load tests

Overview

By default, the k6:run goal uses a ramp load pattern that gradually increases virtual users to the target count, sustains the load, then ramps back down. This produces more realistic traffic than an instant spike and avoids overwhelming the application at startup.

Load profiles control the shape of the traffic curve — how many virtual users (VUs) are active at each point during the test. Three levels of configuration are available:

  1. Predefined patterns — convenient presets (ramp, constant, stress, soak, custom stages) that map to k6’s constant-vus and ramping-vus executors.

  2. Explicit executor selection — direct use of any k6 executor (constant-arrival-rate, shared-iterations, etc.) with full parameter control.

  3. Fully custom scenarios — raw k6 scenario JavaScript for maximum flexibility.

Configuration priority (highest to lowest): k6.customScenario > k6.executor > k6.stages > k6.loadPattern.

Quick Start

Source code
Default behavior (ramp up 10 s, sustain, ramp down 10 s)
mvn k6:run -Dk6.vus=50 -Dk6.duration=2m
Source code
Constant load (no ramping, previous default behavior)
mvn k6:run -Dk6.vus=50 -Dk6.duration=2m -Dk6.loadPattern=constant
Source code
Custom ramp durations
mvn k6:run -Dk6.vus=50 -Dk6.duration=5m -Dk6.rampUp=30s -Dk6.rampDown=15s
Source code
Fully custom stages
mvn k6:run -Dk6.stages="30s:20,1m:50,30s:50,15s:80,1m:80,30s:0"
Source code
Constant arrival rate (explicit executor)
mvn k6:run -Dk6.executor=constant-arrival-rate -Dk6.rate=100 \
    -Dk6.duration=2m -Dk6.preAllocatedVUs=50 -Dk6.maxVUs=200
Source code
Shared iterations (explicit executor)
mvn k6:run -Dk6.executor=shared-iterations -Dk6.vus=50 \
    -Dk6.iterations=1000 -Dk6.duration=5m

Predefined Load Patterns

Pattern Description

ramp (default)

Ramp up to target VUs, sustain at full load, then ramp down to 0. Ramp-up and ramp-down durations are configurable via k6.rampUp and k6.rampDown. Uses k6’s ramping-vus executor.

constant

All VUs start immediately and run for the full duration. No ramp-up or ramp-down phase. Uses k6’s constant-vus executor.

stress

Gradually increases load beyond normal capacity with a spike phase. Stages: 50% VUs → 100% VUs → sustain → 150% spike → ramp down. Useful for finding the breaking point of the application.

soak

Quick ramp-up (5% of duration), extended sustain at target load (90%), quick ramp-down (5%). Designed for long-duration tests to detect memory leaks and gradual degradation.

custom

User-defined stages via the k6.stages parameter. Set automatically when k6.stages is provided.

Ramp Pattern (Default)

The ramp pattern divides the total duration into three phases:

  • Ramp-up — linearly increases VUs from 0 to the target over k6.rampUp duration (default 10s).

  • Sustain — holds at target VUs for the remaining time.

  • Ramp-down — linearly decreases VUs from target to 0 over k6.rampDown duration (default 10s).

The sustain duration is automatically calculated: duration - rampUp - rampDown. If rampUp + rampDown exceeds the total duration, both are scaled down proportionally.

Stress Pattern

The stress pattern is designed to push the application beyond its normal operating limits:

Five stages, each a percentage of total duration:

  1. 10% — ramp to 50% of target VUs

  2. 10% — ramp to 100% of target VUs

  3. 40% — sustain at 100%

  4. 20% — spike to 150% of target VUs

  5. 20% — ramp down to 0

Soak Pattern

The soak pattern maximizes time at target load for long-running stability tests:

Three stages:

  1. 5% of duration — ramp to target VUs

  2. 90% of duration — sustain at target

  3. 5% of duration — ramp down to 0

Custom Stages

For full control, define explicit stages as duration:target pairs. When k6.stages is set, the load pattern is automatically set to custom and the k6.vus / k6.duration parameters are ignored.

Source code
Stage format
duration:target,duration:target,...

  • duration — a k6 time string (10s, 1m, 2m30s, 1h)

  • target — the VU count to ramp to by the end of this stage

Each stage linearly transitions from the previous stage’s ending VU count (or 0 for the first stage) to its own target over the given duration. To hold load steady, repeat the same target in consecutive stages (e.g. 1m:50,30s:50 ramps to 50 then holds at 50 for 30 s).

Source code
Example: gradual ramp with plateau and spike
mvn k6:run -Dk6.stages="30s:20,1m:50,30s:50,15s:80,1m:80,30s:0"

This produces:

Reading the stages left to right:

  1. 30s:20 — ramp from 0 to 20 VUs over 30 seconds

  2. 1m:50 — ramp from 20 to 50 VUs over 1 minute

  3. 30s:50 — hold at 50 VUs for 30 seconds (same target = plateau)

  4. 15s:80 — ramp from 50 to 80 VUs over 15 seconds

  5. 1m:80 — hold at 80 VUs for 1 minute

  6. 30s:0 — ramp down from 80 to 0 over 30 seconds

Explicit Executor Selection

When the predefined patterns are not enough, you can select any k6 executor directly via k6.executor. This gives access to all seven k6 executor types and their full parameter sets.

Setting k6.executor overrides k6.loadPattern.

Available Executors

Executor Description

constant-vus

A fixed number of VUs execute iterations for a specified duration. Equivalent to the constant predefined pattern.

ramping-vus

A variable number of VUs follow configured stages (ramp up, sustain, ramp down). Equivalent to the ramp predefined pattern when used with k6.stages.

per-vu-iterations

Each VU executes a fixed number of iterations. The test ends when all VUs complete their iterations or maxDuration is reached. Useful for ensuring each VU performs an exact workload.

shared-iterations

A fixed total number of iterations is shared among all VUs. The test ends when all iterations complete or maxDuration is reached. Useful for fixed-workload testing (e.g., "process exactly 10,000 requests").

constant-arrival-rate

A fixed number of iterations are started per time unit, regardless of how long each iteration takes. VUs are pre-allocated and recycled as needed. Ideal for testing at a specific request rate (e.g., 100 req/s).

ramping-arrival-rate

A variable number of iterations per time unit, following configured stages. Useful for ramping request rates independently of VU count (e.g., ramp from 0 to 200 req/s).

externally-controlled

VU count is controlled externally via k6’s REST API at runtime. Useful for manual or programmatic load control during exploratory testing.

Arrival-Rate vs VU-Based Executors

The predefined patterns (ramp, stress, soak) are VU-based: they control how many users are active. Arrival-rate executors instead control how many requests per second are sent, regardless of VU count.

When to use arrival-rate executors:

  • You need to test at a specific request rate (e.g., "the system must handle 500 req/s")

  • You want the request rate to remain constant even when response times increase

  • Your SLOs are defined in requests per second rather than concurrent users

When to use VU-based executors:

  • You want to simulate a specific number of concurrent users

  • Response times naturally throttle the load (slow responses = fewer requests per VU)

  • Your load targets are defined as user counts

Examples

Source code
Constant arrival rate: 100 iterations/second for 2 minutes
mvn k6:run -Dk6.executor=constant-arrival-rate -Dk6.rate=100 \
    -Dk6.timeUnit=1s -Dk6.duration=2m \
    -Dk6.preAllocatedVUs=50 -Dk6.maxVUs=200
Source code
Ramping arrival rate: ramp from 0 to 200 req/s, sustain, then ramp down
mvn k6:run -Dk6.executor=ramping-arrival-rate \
    -Dk6.stages="1m:200,3m:200,1m:0" -Dk6.startRate=0 \
    -Dk6.timeUnit=1s -Dk6.preAllocatedVUs=50 -Dk6.maxVUs=300
Source code
Shared iterations: distribute 10,000 requests across 50 VUs
mvn k6:run -Dk6.executor=shared-iterations \
    -Dk6.vus=50 -Dk6.iterations=10000 -Dk6.duration=10m
Source code
Per-VU iterations: each of 20 VUs executes 50 iterations
mvn k6:run -Dk6.executor=per-vu-iterations \
    -Dk6.vus=20 -Dk6.iterations=50 -Dk6.duration=5m
Source code
Externally controlled: start with 10 VUs, adjust via k6 REST API
mvn k6:run -Dk6.executor=externally-controlled \
    -Dk6.vus=10 -Dk6.maxVUs=200 -Dk6.duration=30m

POM Configuration for Explicit Executors

Source code
XML
<plugin>
    <groupId>com.vaadin</groupId>
    <artifactId>testbench-converter-plugin</artifactId>
    <configuration>
        <testDir>${project.build.directory}/k6/tests</testDir>
        <executor>constant-arrival-rate</executor>
        <rate>100</rate>
        <timeUnit>1s</timeUnit>
        <duration>5m</duration>
        <preAllocatedVUs>50</preAllocatedVUs>
        <maxVUs>200</maxVUs>
    </configuration>
</plugin>
Source code
Ramping arrival rate with stages
<configuration>
    <testDir>${project.build.directory}/k6/tests</testDir>
    <executor>ramping-arrival-rate</executor>
    <stages>1m:100,3m:100,1m:0</stages>
    <startRate>0</startRate>
    <timeUnit>1s</timeUnit>
    <preAllocatedVUs>50</preAllocatedVUs>
    <maxVUs>200</maxVUs>
</configuration>
Note
 Executors other than constant-vus and ramping-vus cannot be fully configured via k6 CLI flags. When these executors are used, the plugin automatically generates a wrapper script with embedded scenario configuration.

Fully Custom Scenarios

For maximum flexibility, use k6.customScenario to provide raw k6 scenario JavaScript. The content is inserted directly into the k6 scenario definition block, giving full control over all scenario properties.

This overrides all other load configuration parameters.

Source code
Command line
mvn k6:run -Dk6.customScenario="executor: 'ramping-arrival-rate', \
    startRate: 0, timeUnit: '1s', preAllocatedVUs: 50, maxVUs: 100, \
    stages: [{duration: '1m', target: 100}, {duration: '2m', target: 100}, \
    {duration: '1m', target: 0}],"
Source code
POM configuration (recommended for complex scenarios)
<configuration>
    <testDir>${project.build.directory}/k6/tests</testDir>
    <customScenario>
        executor: 'ramping-arrival-rate',
        startRate: 0,
        timeUnit: '1s',
        preAllocatedVUs: 50,
        maxVUs: 100,
        stages: [
            { duration: '1m', target: 100 },
            { duration: '2m', target: 100 },
            { duration: '1m', target: 0 },
        ],
    </customScenario>
</configuration>

The content must be valid JavaScript object properties (k6 scenario syntax). The plugin adds the exec property automatically to wire up the test function.

Maven Configuration

Command Line (Predefined Patterns)

Source code
bash
# Ramp pattern with custom durations
mvn k6:run -Dk6.vus=100 -Dk6.duration=10m -Dk6.loadPattern=ramp \
    -Dk6.rampUp=1m -Dk6.rampDown=30s

# Stress test
mvn k6:run -Dk6.vus=100 -Dk6.duration=10m -Dk6.loadPattern=stress

# Soak test (long duration)
mvn k6:run -Dk6.vus=50 -Dk6.duration=1h -Dk6.loadPattern=soak

# Custom stages
mvn k6:run -Dk6.stages="1m:25,3m:50,1m:100,2m:100,1m:0"

POM Configuration (Predefined Patterns)

Source code
XML
<plugin>
    <groupId>com.vaadin</groupId>
    <artifactId>testbench-converter-plugin</artifactId>
    <configuration>
        <testDir>${project.build.directory}/k6/tests</testDir>
        <virtualUsers>50</virtualUsers>
        <duration>5m</duration>
        <loadPattern>ramp</loadPattern>
        <rampUp>30s</rampUp>
        <rampDown>15s</rampDown>
    </configuration>
</plugin>
Source code
Stress test configuration
<configuration>
    <testDir>${project.build.directory}/k6/tests</testDir>
    <virtualUsers>100</virtualUsers>
    <duration>10m</duration>
    <loadPattern>stress</loadPattern>
</configuration>
Source code
Custom stages configuration
<configuration>
    <testDir>${project.build.directory}/k6/tests</testDir>
    <stages>1m:25,3m:50,1m:100,2m:100,1m:0</stages>
</configuration>

Parameter Reference

Predefined Pattern Parameters

Property Type Default Description

k6.loadPattern

String

ramp

Load pattern: constant, ramp, stress, soak, or custom.

k6.rampUp

String

10s

Ramp-up duration for the ramp pattern. Ignored for other patterns.

k6.rampDown

String

10s

Ramp-down duration for the ramp pattern. Ignored for other patterns.

k6.stages

String

none

Custom stage definitions (duration:target,…​). When set, overrides k6.loadPattern to custom.

k6.vus

int

10

Target number of virtual users. Used by all patterns except custom.

k6.duration

String

30s

Total test duration. Used by all patterns except custom.

Explicit Executor Parameters

Property Type Default Description

k6.executor

String

none

Explicit k6 executor type. Overrides k6.loadPattern when set. Valid values: constant-vus, ramping-vus, per-vu-iterations, shared-iterations, constant-arrival-rate, ramping-arrival-rate, externally-controlled.

k6.rate

Integer

none

Iteration rate for arrival-rate executors. Number of iterations to start per k6.timeUnit.

k6.timeUnit

String

1s

Time unit for arrival-rate executors (e.g., 1s, 1m).

k6.preAllocatedVUs

Integer

none

Pre-allocated VUs for arrival-rate executors. k6 initializes this many VUs at test start to avoid cold-start latency. Defaults to k6.vus if not specified.

k6.maxVUs

Integer

none

Maximum VUs for arrival-rate and externally-controlled executors. k6 will not create more VUs than this, even if the arrival rate demands it.

k6.iterations

Integer

none

Total iteration count for per-vu-iterations (per VU) and shared-iterations (total across all VUs).

k6.startRate

Integer

none

Starting iteration rate for ramping-arrival-rate. The rate ramps from this value according to the configured stages.

Custom Scenario Parameter

Property Type Default Description

k6.customScenario

String

none

Raw k6 scenario JavaScript. Inserted directly into the scenario definition block. Overrides all other load configuration parameters when set.

Combined Scenarios

Load profiles work with combined scenario execution (k6.combineScenarios=true). Each scenario receives its own proportional VU allocation based on weights, and all scenarios share the same load profile shape.

This applies to all configuration modes — predefined patterns, explicit executors, and custom scenarios.

Source code
bash
mvn k6:run -Dk6.testDir=k6/tests -Dk6.combineScenarios=true \
    -Dk6.vus=100 -Dk6.duration=5m -Dk6.loadPattern=ramp -Dk6.rampUp=30s

With two equally-weighted scenarios, each gets 50 VUs and follows the ramp pattern independently:

Source code
Scenario A:  0 ──30s──> 50 VUs ──sustain──> 50 VUs ──10s──> 0
Scenario B:  0 ──30s──> 50 VUs ──sustain──> 50 VUs ──10s──> 0
Source code
Combined scenarios with arrival-rate executor
mvn k6:run -Dk6.testDir=k6/tests -Dk6.combineScenarios=true \
    -Dk6.executor=constant-arrival-rate -Dk6.rate=100 \
    -Dk6.duration=5m -Dk6.preAllocatedVUs=50 -Dk6.maxVUs=200

Duration Format

All duration parameters accept k6 time strings:

Format Example

Seconds

30s

Minutes

5m

Hours

1h

Combined

2m30s, 1h30m, 1h30m30s

Choosing a Configuration

Goal Recommended Configuration

Baseline performance measurement

ramp pattern with short ramp durations (5s-10s)

Capacity planning

ramp pattern with gradual ramp (1m+) to observe behavior as load increases

Finding breaking points

stress pattern to push beyond normal capacity

Memory leak detection

soak pattern with long duration (30m-1h+)

CI/CD smoke test

constant pattern with low VUs and short duration

Reproducing specific traffic shapes

custom stages matching production patterns

Testing at a specific request rate

constant-arrival-rate executor with target rate

Ramping request rate independently of VUs

ramping-arrival-rate executor with rate stages

Fixed workload testing (exact request count)

shared-iterations executor with target iteration count

Ensuring each user does equal work

per-vu-iterations executor with per-VU iteration count

Manual / exploratory load control

externally-controlled executor with k6 REST API

Complex multi-executor scenarios

k6.customScenario with raw k6 JavaScript