parallel-testing with SeleniumGrid and headless Chrome - selenium-grid

Question

I try to run the same end2end test parallel (load test, JMeter with JUnitSampler).
If i run parallel tests with real chromeBrowser, its working fine. If i run the Tests with chromeOption “--headless”, no tests are running. What could be the difference between real chromeBrowser and headless chromeBrowser?
One test with headlessBrowser (not parallel) is also running well.
Step1 - JUnit Test:
public class AppTest extends TestCase{
private Logger logger;
private WebDriver driver;
private String user;
private String passwd;
#Before
#Override
public void setUp() throws MalformedURLException {
logger = LoggerFactory.getLogger(AppTest.class);
user = “user”;
passwd = “12345”;
DesiredCapabilities caps = DesiredCapabilities.chrome();
ChromeOptions chromeOptions = new ChromeOptions();
chromeOptions.addArguments(“--headless”);
chromeOptions.addArguments(“--incognito”);
caps.setCapability(ChromeOptions.CAPABILITY, chromeOptions);
driver = new RemoteWebDriver(new URL(“http://127.0.0.1:4444/wd/hub”), caps);
driver.manage().timeouts().implicitlyWait(20, TimeUnit.SECONDS);
}
#Test
public void workFlow() throws InterruptedException {
driver.get("https://somesite.de");
try {
WebElement input = driver.findElement(By.id(“login-form-username”));
input.click();
input.clear();
input.sendKeys(user);
} catch (NoSuchElementException e) {
fail(“Element not found”);
}
try {
Thread.sleep(1000);
WebElement myButton = driver.findElement(By.className("my-button”));
myButton.click();
} catch (NoSuchElementException e) {
fail(“Element not found”);
}
try {
Thread.sleep(2000);
WebElement input = driver.findElement(By.id(“password-form-password”));
input.click();
input.sendKeys(passwd);
} catch (NoSuchElementException e) {
fail(“Element not found”);
}
try {
WebElement myButton = driver.findElement(By.className(“my-button”));
myButton.click();
} catch (NoSuchElementException e) {
fail(“Element not found”);
}
try {
Thread.sleep(2000);
List<WebElement> displayBoxHeaders = driver.findElements(By.className(“box-complete-header”));
assertThat(displayBoxHeaders.get(1).getText()).contains(user);
WebElement logo = displayBoxHeaders.get(0);
String svg = logo.findElement(By.tagName(“svg”)).findElement(By.tagName(“g”)).findElement(By.tagName(“path”)).getAttribute(“class”);
assertThat(svg).isNotNull().isNotEmpty();
} catch (NoSuchElementException e) {
fail();
}
try {
WebElement displayText = driver.findElement(By.id(“ui-form-text”));
String text = displayText.getText();
assertThat(text).isNotNull().isNotEmpty();
} catch (Exception e) {
fail();
}
try {
WebElement myButton = driver.findElement(By.className(my-button”));
myButton.click();
} catch (NoSuchElementException e) {
fail(“Element not found”);
}
}
#After
public void tearDown() {
if (driver != null) {
driver.quit();
}
}
Step2 - JUnitSampler in JMeter with JUnitTestClass above.
Step3 - SeleniumGrid in Docker
git clone https://github.com/SeleniumHQ/docker-selenium.git
cd docker-selenium
docker run -d -p 4444:4444 --name selenium-hub selenium/hub:3.5.3-boron
docker run -d --link selenium-hub:hub -e NODE_MAX_INSTANCES=100 -e NODE_MAX_SESSION=100 selenium/node-chrome:3.5.3-boron
Step3 - Run single Thread in JMeter:
Test runs successfully.
Step4 - Run 5 Threads in parallel in JMeter:
First test runs successfully, other four not.
Error: is ElementNotFound in each failed test run
It is important for the test that the browser instances do not have the same session.