Get started today
Replay past traffic, gain confidence in optimizations, and elevate performance.

GoReplay and Speedscale are two popular tools commonly used for load testing. Both share traffic shadowing as a core feature. This article compares both tools against the following criteria:

  • Ease of setup
  • Developer experience
  • CI/CD integration

For more Kubernetes load testing comparisons, check out our other posts:

Kubernetes Load Testing: Top 5 Tools & Methodologies

Compare tools & learn the best methodologies for efficient Kubernetes load testing, and see how to ensure performance of your app under load.

Traffic shadowing: A brief overview and benefits

Traffic shadowing, also known as traffic mirroring, is a software testing approach that allows you to record real user traffic, and replay it later against any service. By generating test traffic that replicates how real people use your app, software testing is more accurate and realistic.

Shadowing traffic allows you to:

  • Stop manually writing tests
  • Test networking rules, such as the API gateway or Ingress level
  • Leverage real user traffic to generate tests
  • Use traffic to test autoscaling rules
  • Use recorded traffic to test circuit breaker patterns/failovers


Ease of setup: GoReplay vs. Speedcale

Setting up Speedscale

Speedscale requires a few steps to get started. The provided Quick Start Guide is easy to follow and has three distinct sections:

  • Install
  • Observe
  • Replay

Speedscale can be installed using Helm or by utilizing Speedscale’s own speedctl CLI tool. For both options, the Quick Start Guide provides the exact commands you will need, which you can copy & paste into your terminal.

Helm is one of several installation options. Speedscale does not work by installing onto your local system, rather, it installs directly into your Kubernetes cluster as an Operator. Once you use the Helm chart or the speedctl tool to instrument your services with Speedscale, you’re ready to start.

Setting up GoReplay

GoReplay has a somewhat simpler installation process. To get started, you need to download the latest binary from the release page. With the binary downloaded, you then need to add it to your PATH. On Linux, this could mean moving it to /usr/local/bin. At this point, you’re ready to start using GoReplay.

While GoReplay is the easier tool to set up, this is largely because it has less functionality, and doesn’t integrate directly with Kubernetes. Speedscale was designed to support the Kubernetes space specifically, whereas GoReplay is more focused on HTTP traffic in general.

This means you don’t need any specific prior knowledge of GoReplay to use it, while Speedscale requires you to have at least a basic understanding of Kubernetes. If you’re looking for a Kubernetes load testing tool, it’s safe to assume this won’t be an issue.

Generating traffic with Speedscale

To shadow a service with Speedscale, you first need to instrument your service using the speedctl tool. Instrumenting a service with Speedscale adds a sidecar to your service. This sidecar acts as a proxy and captures all traffic going in and out of your service.

This ensures Speedscale will always capture all the traffic linked to your instrumented service–therefore, you will always have relevant traffic available to create snapshots and use.

With a snapshot of traffic saved in Speedscale, you can now replay that traffic to any service in your Kubernetes cluster. This is done either by clicking “Replay” in the Speedscale WebUI, adding annotations to an existing deployment, or by pushing a new deployment with given annotations.

Speedscale’s Replay traffic feature

Generating traffic with GoReplay

As there is no WebUI for GoReplay, you will spend a lot more time in the terminal. To capture traffic with GoReplay, you need to run:

$ sudo gor –input-raw :8000 –output-file ./requests.gor

This will save all requests to a file. The –input-raw :8000 defines that GoReplay will record any traffic that occurs on port 8000.

Important note: GoReplay needs to run on the same system that you want to record traffic. In a Kubernetes setup, this can be tricky. The best approach is to add a GoReplay container to your pod, use that container to record the traffic, and then save the recorded requests to some persistent storage.

Also, note that GoReplay is not a proxy. Instead, it creates a hook at the system level and records any traffic occurring at the HTTP socket, on a given port.

Once traffic has been recorded, you can use almost the same command to replay the traffic:

$ sudo gor –input-file ./requests.gor –output-http http://staging.example.com

As a GoReplay alternative, Speedscale is continuously recording traffic. GoReplay requires you to manually set up the tool and save the files somewhere, plus, it only collects and replays inbound traffic. Speedscale allows you to mock outgoing requests, so you only load test your own service.

While GoReplay is a great tool, Speedscale wins when it comes to testing services inside a Kubernetes cluster. We’ve shown you how shadowing is implemented in each of these services–the principles of regular load testing are the same. Speedscale allows you to modify the captured traffic and generate more powerful load tests. By comparison, GoReplay only allows you to replay the captured traffic (unless you manually edit the file of the captured requests).


Developer experience

When it comes to tool implementation, Speedscale requires more steps, and GoReplay is as simple as downloading a binary. When you start using these tools, however, you may notice that GoReplay lags behind, as Speedscale has a lot more features and is specifically built for Kubernetes.

If you have a service that you’re running locally, such as a new service or feature that you’re developing, GoReplay is probably the most optimal. It allows you to capture traffic and replay it locally, which is great for a quick and easy test.

When you need to implement shadowing and load testing within your infrastructure–as part of your CI/CD pipeline, for example–Speedscale is a better choice. Overall, Speedscale offers a more comprehensive tool for load testing, as well as API mocking and traffic visualization.

API Mocking: Top 8 Tools & Methodologies

Understand the key benefits, drawbacks, and use cases for Postman, MockServer, GoMock, MockAPI, and Speedscale.

CI/CD integration

When starting with load testing, most development teams do a one-off test to ensure that their application can handle the expected load.

As the organization and infrastructure grows, however, most teams realize that including load tests as part of their CI/CD pipeline can yield major benefits, such as:

  • Continuous feedback on the resiliency of their application
  • More trust in the CI/CD pipeline, with more parts of the application being tested
  • Closer proximity to continuous deployments, as more parts of the application are verified

So, how easily do Speedscale and GoReplay integrate into a CI/CD pipeline?

Integrating with Speedscale

Speedscale has detailed instructions for integrating with CI/CD providers. Depending on the CI/CD provider you choose, specific integration steps can vary a bit, but they all boil down to this basic sequence:

  • Create a snapshot
  • Deploy the test
  • Fetch the report
  • If the status says “PASSED”, the check will pass

You can find detailed instructions for integrating with specific CI/CD providers within Speedscale’s documentation. All integrations utilize the speedctl CLI tool, so if your CI/CD provider is not on the list, you should be able to implement a script yourself.

Integrating with GoReplay

As a comparison, GoReplay provides no specific official instructions for integrating with a CI/CD provider, so you must create a custom script.

Before you implement this script, it’s assumed that you’ve used the gor CLI tool to create a file of requests. This file needs to be uploaded (or accessible) to your CI/CD server.

With access to the replay file, you can now run your load test by running:

$ sudo gor –input-file ./requests.gor –output-http http://staging.example.com

While this part is easy with GoReplay, there are a few other areas that you’ll need to handle yourself, which Speedscale handles for you.

The next step is to spin up a new instance of your application where you’ll perform your load test; then, run the test. Verifying that the requests were successful will require a third-party approach, as this capability is not supported by GoReplay. Then, you need to pass that verification off to the CI/CD provider.


Deciding which tool is best for you

In the end, both tools let you record traffic and replay it, and accomplish the goal of traffic shadowing. While GoReplay is a great tool for replaying traffic locally, using it efficiently in a Kubernetes setup is a challenge, so Speedscale may be a better fit for modern architectures.

Speedscale has always been focused on matching the modern nature of a Kubernetes setup. Not only does it integrate directly with your cluster via the sidecar mechanism, Speedscale’s deeper intelligence allows for more flexible shadowing.

Take for example, a service where requests must be within a certain prior timestamp (e.g. within the past 2 hours). You’ll have an issue if you record your traffic and replay it 3 hours later, as the timestamp is outdated.

Speedscale can automatically detect this gap and shift the timestamp, so it will still match the age criteria. This automatic detection is also the case with tokens and unique IDs. Even if Speedscale can’t detect and change the values automatically, you can manually configure Traffic Transforms.

When it comes to shadowing in Kubernetes especially, Speedscale will likely provide a much better experience since it was built for containers. If you’re still not sure what tool is best for you, check out our other load testing tool comparisons:

Happy load testing!

Learn more about Kubernetes load testing


Getting Started with Speedscale


Test Load with Real User Data

Ensure performance of your Kubernetes apps at scale

Auto generate load tests, environments, and data with sanitized user traffic—and reduce manual effort by 80%
Start your free 30-day trial today