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Global Custom Attributes

Available since Router version 0.92.0.
Attributes based on request header values may potentially leak sensitive information when stored on the telemetry storage provider. You should only attach headers that have been sanitized by your infrastructure.
Each attribute increases the cardinality of a metric. Higher cardinality can be costly, as it increases the system’s memory usage and processing overhead.To mitigate this, a limit of 2,000 unique combinations (variations) per metric is enforced. When this limit is exceeded, a new metric—without any attributes—is created and used instead. This approach helps maintain system stability and prevents excessive memory consumption.
There are scenarios where you may want to add additional attributes to your metrics and spans. One common use case is to add environment information, such as env=prod. We provide an easy way to achieve this by adding a few lines of configuration.

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Prometheus

All attributes are also added to the Prometheus metrics. Resource attributes are special and are only added as labels to the target_info metric.

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Static Attribute Value

telemetry:
  resource_attributes:
    - key: env
      value: "prod"
  attributes:
    - key: service
      default: "static"
This configuration will add the resource attribute env=prod to every metric and span export. Additionally, the attribute service=static is also added. Resource attributes identify the entity producing the traces and metrics. Since Prometheus metrics rely on OpenTelemetry metrics, the resource attributes are also added to the Prometheus target_info series.

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Dynamic Attribute Value

We also support setting attributes based on client request headers. To do this, simply specify the mapping in the value_from property. If the headers could not be found, we will fallback to the default value. This functionality is only available to attributes not resource_attributes. 
cors:
  allow_headers:
    - "x-service"

telemetry:
  attributes:
    - key: service
      default: "static"
      value_from:
        request_header: "x-service"
This will add the attribute service=static unless the client has provided a request header x-service, in which case the value of this header will be used instead of the default value. Remember to add the header to the allowlist in the CORS configuration; otherwise, CORS issues will occur on the frontend.

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Expression Attributes

We also support using expressions for telemetry attributes (as well as metrics and tracing). 
telemetry:
  attributes:
    - key: "url_method"
      value_from:
        expression: "request.url.method"
The above will attach the key “url_method” with the appropriate value to all spans and metrics. Note that when attaching values from expressions, if the value is not present at the time of evaluation it will not be attached. Users can also use subgraph expressions in telemetry metrics as follows: 
telemetry:
  attributes:
    - key: "sg_name"
      value_from:
        expression: "subgraph.name"
Unlike previously in this case, any expression with subgraph in it, will only be evaluated for the “Engine - Fetch” span. Thus “sg_name” can only be found in the “Engine - Fetch” span. You can find more information about expressions and the fields accessible for expressions here.
At the moment, we only allow expressions to return string values. If, for example, an expression returns an integer, you will need to cast it using exprlang’s string function.

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Metrics Only Attributes

Available since Router version 0.126.0.
While using the telemetry configuration allows users to specify attributes which will be attached to both spans AND metrics, there may be cases users want to attach values to metrics only. In this case you can use metrics only attributes. 
cors:
  allow_headers:
    - "x-service"

telemetry:
  metrics:
    attributes:
      - key: service
        default: "static"
        value_from:
          request_header: "x-service"
      - key: "error_codes"
        value_from:
          context_field: graphql_error_codes
The above configuration will ensure that the attribute service will only be attached to metrics. Headers are pre-evaluated before metrics are emitted, while request context fields are determined at different stages. Consequently, request context fields may not be included in all metrics. Additionally, the unique list of subgraph error codes will be appended to all emitted metric values. This enables correlation between error cases and corresponding metrics.

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Tracing Only Attributes

Available since Router version VERSION.
While using the telemetry configuration allows users to specify attributes which will be attached to both spans AND metrics, there may be cases users want to attach values to spans only. In this case you can use trace only attributes. 
cors:
  allow_headers:
    - "x-service"

telemetry:
  trace:
    attributes:
      - key: service
        default: "static"
        value_from:
          request_header: "x-service"
The above configuration will ensure that the attribute service will only be attached to spans. For a complete list of available options, please refer to the relevant documentation section.