Seamless Service Migration with Shadow Traffic

When you’re building a new service to replace an old one, ensuring it works flawlessly is crucial. One powerful technique to achieve this is called shadow traffic.

But what exactly is shadow traffic, and why is it so important?

What Is Shadow Traffic?

In a typical system, your old service handles all incoming requests — it receives HTTP requests, processes them, and returns the appropriate data response.

When you develop a new service, you don’t want to switch all traffic to it immediately without thorough testing. This is where shadow traffic comes into play.

How Does Shadow Traffic Work?

1. You take the incoming request that the old service is processing and duplicate it. This duplicate request is also sent to the new service.
2. The new service processes the duplicated request and generates its own response.
3. After both services have processed the request, their responses are compared. This comparison can happen in real-time or later. The goal is to ensure that the new service behaves similarly to the old one.

The diagram is taken as an example from zalando.com

Why Use Shadow Traffic?

The main benefit of shadow traffic is that it allows you to test the new service under the same conditions as the old one without affecting actual user experiences.

Unlike canary testing (where a small portion of real traffic is routed to the new service), shadow traffic tests the new service in a controlled environment. This means:

• Users continue to interact with the old service without any disruptions.
• You get to see how the new service performs with real-world data.
• Any issues in the new service won’t affect live traffic

A Key to Smooth Transitions

By using shadow traffic, development teams can ensure that the new service is nearly identical to the old one in functionality.

It helps answer the critical question: Is the new service ready for the real world?

This technique is essential for:

• Confirms that the new service can handle real traffic loads.
• Checks if the new service meets performance benchmarks.
• Guarantees that users won’t be negatively impacted during the migration.

Conclusion

Shadow traffic is a powerful tool in software development. It helps teams confidently migrate to new systems by validating performance, accuracy, and stability in a risk-free environment. By incorporating shadow traffic into your testing strategy, you pave the way for a seamless and successful service transition.

Cheers and Good Luck! 👋