Run Gatling Load Tests in GitHub Actions CI (2026)

Gatling tests in GitHub Actions can fail for a variety of reasons, but the most common culprit is the Gatling process itself crashing due to resource exhaustion or misconfiguration within the CI environment.

Common Causes and Fixes

Insufficient Memory Allocation for Gatling:
- Diagnosis: Look for errors like java.lang.OutOfMemoryError: Java heap space in the Gatling logs within your GitHub Actions job.
- Fix: Increase the JVM heap space allocated to Gatling. In your GitHub Actions workflow, modify the command that runs Gatling to include JVM options:
```
- name: Run Gatling Load Test
  run: |
    ./gatling.sh -rm local -nr -rf ./results -s your.package.Simulation
  env:
    JAVA_OPTS: "-Xms4g -Xmx8g" # Example: 4GB initial, 8GB max heap
```
- Why it works: Gatling, being a JVM-based tool, requires sufficient memory to manage its simulation state, record metrics, and generate reports. The default allocation might be too small for complex simulations or high load levels.
GitHub Actions Runner Resource Limits:
- Diagnosis: The entire GitHub Actions runner might become unresponsive or the job might be terminated abruptly without a clear Gatling error. Check the runner’s system logs if accessible, or observe overall job duration and resource utilization metrics provided by GitHub Actions.
- Fix: Switch to a larger GitHub Actions runner type. If you’re on a self-hosted runner, ensure it has adequate CPU and RAM. For GitHub-hosted runners, consider using runs-on: ubuntu-22.04 or a more powerful instance type if available through enterprise plans.
```
jobs:
  load_test:
    runs-on: ubuntu-22.04 # Or a more powerful GitHub-hosted runner
    # ... rest of your job
```
- Why it works: GitHub-hosted runners have finite resources. A load test that simulates high concurrency can quickly consume CPU or memory on the runner itself, leading to instability or termination of the entire job process.
Incorrect Gatling Simulation Configuration:
- Diagnosis: Gatling might start but fail to execute scenarios, or report errors related to missing configurations or invalid scenario definitions. Check the gatling.conf file for syntax errors or missing essential parameters.
- Fix: Ensure your gatling.conf is correctly placed and formatted. Pay close attention to http.baseUrl, core.directory.reports, and core.directory.results.
```
# Example gatling.conf snippet for CI
http {
  baseUrl = "http://your-target-api.com"
}

core {
  directory {
    reports = "results"
    results = "results"
  }
}
```
- Why it works: Gatling relies on its configuration file for critical settings like the base URL of the system under test and where to store output. Errors here prevent the simulation from running against the correct target or storing results properly.
Network Connectivity Issues to the Target System:
- Diagnosis: Gatling logs will show a high rate of connection errors, timeouts, or java.net.ConnectException when trying to reach the target API.
- Fix: Verify that the GitHub Actions runner has network access to your target system. If your target system is behind a firewall or VPC, ensure the runner’s IP addresses are whitelisted or that you’re using a self-hosted runner within the same network.
```
# In your workflow, before running Gatling
- name: Check network connectivity
  run: |
    curl -v http://your-target-api.com/health # Or any endpoint
```
- Why it works: The CI runner needs to be able to establish TCP connections to the servers it’s testing. Network restrictions are a common cause of load test failures in isolated CI environments.
Missing Gatling Dependencies or Incorrect Build Setup:
- Diagnosis: The Gatling executable might not be found, or it might report errors about missing classes or libraries when you try to run it.
- Fix: Ensure your build process correctly downloads and extracts the Gatling distribution and that the gatling.sh (or gatling.bat) script is executable and in your PATH or called with its relative path.
```
- name: Setup Gatling
  run: |
    wget https://repo1.maven.org/maven2/io/gatling/highcharts/gatling-charts-highcharts-bundle/3.8.1/gatling-charts-highcharts-bundle-3.8.1-bundle.zip
    unzip gatling-charts-highcharts-bundle-3.8.1-bundle.zip
    mv gatling-charts-highcharts-3.8.1 gatling
    echo "$PWD/gatling/bin" >> $GITHUB_PATH # Add to PATH
```
- Why it works: Gatling is typically distributed as a zip file containing scripts and libraries. The CI environment needs to have these files present and accessible for the simulation to launch.
Large Report Generation Overwhelming Storage or CI Limits:
- Diagnosis: The job might fail with disk space errors, or the Gatling report generation step might hang indefinitely.
- Fix: Disable detailed HTML report generation in CI or configure Gatling to generate only summary statistics. You can do this by setting core.directory.reports to a non-existent path or by using command-line flags to disable report generation. Alternatively, archive only essential results like simulation.log and stats.json.
```
- name: Run Gatling Load Test
  run: |
    ./gatling.sh -rm local -nr -rf ./results -s your.package.Simulation
  env:
    JAVA_OPTS: "-Dgatling.core.directory.reports=false" # Disables HTML report generation
```
- Why it works: Generating detailed HTML reports can consume significant disk space and CPU resources, which are often limited in CI environments. Disabling this or focusing on raw data prevents CI job failures due to resource constraints.

The next error you might encounter after fixing these issues is related to the analysis of the Gatling results within the CI, such as problems uploading large artifact files or parsing the simulation.log for specific performance regressions.