istio.io/content/en/docs/reference/glossary/attribute.md

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Attributes control the runtime behavior of services running in the mesh. Attributes are named and typed pieces of metadata describing ingress and egress traffic and the environment this traffic occurs in. An Istio attribute carries a specific piece of information such as the error code of an API request, the latency of an API request, or the original IP address of a TCP connection. For example:

{{< text yaml >}} request.path: xyz/abc request.size: 234 request.time: 12:34:56.789 04/17/2017 source.ip: 192.168.0.1 destination.workload.name: example {{< /text >}}

Attributes are used by Istio's policy and telemetry features.