Great call using Fiddler for debugging—it’s way more intuitive to inspect request/response details than digging through console logs! Here’s how to route your Gatling traffic through Fiddler step by step:

1. Configure Gatling to Use Fiddler as a Proxy #

Gatling’s HTTP client needs explicit proxy settings to send traffic through Fiddler. Add this to your script’s HTTP protocol definition:

val httpProtocol = http
  .baseUrl("https://your-target-server.com") // Replace with your actual target URL
  .proxy(Proxy("localhost", 8888).httpsPort(8888))

• Fiddler uses port 8888 by default—use this for both HTTP and HTTPS traffic, since Fiddler handles HTTPS decryption automatically once set up.

2. Enable HTTPS Decryption in Fiddler #

If your test sends HTTPS requests (which most modern apps do), you need Fiddler to decrypt traffic so you can view raw content:

• Open Fiddler, go to Tools > Options > HTTPS
• Check the box for "Decrypt HTTPS traffic"
• Follow the prompts to install Fiddler’s root certificate (this is safe—it’s a local certificate only used to intercept traffic on your machine)

3. Fix SSL Trust Issues (If Encountered) #

Sometimes Gatling’s JVM won’t trust Fiddler’s certificate, leading to SSL errors. If this happens:

• Locate Fiddler’s root certificate (usually Documents/Fiddler2/FiddlerRoot.cer on Windows, or ~/Library/Application Support/FiddlerCore/FiddlerRoot.cer on Mac)
• Add a JVM argument when running Gatling to trust this certificate:

  -Djavax.net.ssl.trustStore=/path/to/FiddlerRoot.cer
  

  Alternatively, import the certificate into your JVM’s default cacerts store for persistent trust across all Gatling runs.

4. Test and Validate #

• Make sure Fiddler is running before starting your Gatling test
• Run your script, then check Fiddler’s session list—you’ll see all requests from Gatling appear here
• Click any session to inspect request headers, payloads, response codes, and body content—perfect for verifying your script sends the correct data!

Quick Tips #

• Remove the proxy configuration from your script when running production load tests—routing traffic through Fiddler adds latency and will bottleneck your results
• If you don’t see traffic in Fiddler, double-check that Gatling’s proxy port matches Fiddler’s configured port (confirm in Tools > Options > Connections)

内容的提问来源于stack exchange，提问作者CamHart