How can one distinguish between a regular call and a retried call in Istio?

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In Istio, a retried call is an attempt to retry a failed request to a service. To distinguish between a regular call and a retried call, you can use Istio's distributed tracing capabilities to track the request through the service mesh. Specifically, you can use the following steps:

1. Enable distributed tracing in Istio by deploying a tracing backend such as Jaeger or Zipkin.

2. Modify the code of the service to include a unique identifier in the request headers. This identifier can be used to track the request through the service mesh.

3. When a request is made to the service, the unique identifier is included in the request headers.

4. If the request fails and is retried, a new unique identifier is generated and included in the request headers.

5. The unique identifier can be used to distinguish between a regular call and a retried call in the tracing data. For example, the tracing data may show multiple requests with the same source and destination, but with different unique identifiers, indicating that a retried call occurred.