API Replay Testing or Traffic Mirroring to compare how 2 different services handle the same request. (Question)

[vruss]

Hello, I am making this issue as more of a help wanted on if it's possible to do what I am required to do using your library.

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As a developer,
I want to perform API Replay Testing by capturing and replaying real-world traffic from the old service to a new service or Mirror the traffic in real time,
so that I can ensure the new service produces consistent responses and maintains compatibility with all clients.

Acceptance Criteria:

1. Traffic Capture:

   • Capture real API traffic from the old service, including headers, request payloads, and responses, using a reverse proxy.

2. Traffic Replay:

   • Reuse the captured traffic and replay the same requests against the new service.

3. Response Comparison:

   • Compare responses between the old and new services for:
     • HTTP status codes
     • Response body structure and content
     • HTTP headers
   • Implement automated comparison logic to detect and log any discrepancies.
   • Account for non-deterministic fields (e.g., timestamps, unique IDs) in the comparison process.

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Is it possible to do these things using a Middleware? Since this kind of replay testing / mirroring is not unique I'm curious if it there already exists a finished solution for this.

[MihaZupan]

In short, no such functionality currently exists in the library, but you should be able to build such functionality on top of it.
See #105 and #2075 for more discussions around this & things to watch out for.

It should be relatively straightforward if you're only dealing with simple GET requests, otherwise you run into a lot more things to consider.

Traffic Capture / Traffic Replay

Do you mean mirroring of only live traffic?

There are existing tools that let you capture/persist networking traffic to replay later, have you tried using something like that?

if it there already exists a finished solution for this.

None that I can point you at, but maybe someone from the community can share how they've approached it.