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Shadow Mode Execution

Shadow Mode in Solvix allows you to send requests to a secondary backend alongside the primary request.

The response from the secondary backend does not affect the main response but can be used for comparison, testing, and validation.

Why Shadow Mode?​

In production systems:

  • You may want to test a new backend
  • You may migrate services gradually
  • You may validate responses without impacting users

Shadow mode enables safe experimentation.

Basic usage​

const client = createClient({
  shadow: {
    enabled: true,
    secondaryBaseURL: "https://shadow-api.example.com",
  },
});

How it works​

  1. Primary request is executed normally
  2. Shadow request is sent in parallel
  3. Primary response is returned
  4. Shadow response is used internally

Example​

await client.get("/users", {
  shadow: {
    enabled: true,
    secondaryBaseURL: "https://new-api.example.com",
  },
});

Response comparison​

shadow: {
  enabled: true,
  secondaryBaseURL: "https://new-api.example.com",
  compareResponse: true
}

If responses differ:

  • Callback is triggered
  • Event is emitted

Difference handler​

shadow: {
  compareResponse: true,
  onDifference: (primary, secondary) => {
    console.log("Mismatch detected");
  }
}

Use cases​

Backend migration​

  • Test new API without breaking users

A/B testing​

  • Compare system performance

Debugging​

  • Detect inconsistencies

Important notes​

  • Shadow request NEVER affects main response
  • Errors in shadow mode are ignored
  • Runs in background

Performance impact​

  • Minimal overhead
  • Runs asynchronously
  • Does not block primary request

Best practices​

  • Use only in staging or controlled environments
  • Monitor differences carefully
  • Avoid sensitive data leakage

Summary​

Shadow Mode allows safe testing of new systems without impacting production behavior.