Class PrometheusComposedMetricSource<V>

A ComposedMetricSource that fetches composed metrics from Prometheus.

Naming Scheme: Composed metrics that are stored in Prometheus use the following naming scheme:

polaris_composed_<metricType>{

    // Group Version Kind string of the SLO Target resource.
    target_gvk="ObjectKind.stringify(sloTarget)",

    // Namespace of the SLO Target resource (not to be confused with the `namespace` label added by Prometheus).
    target_namespace="sloTargetNamespace",

    // Name of the SLO Target resource.
    target_name="sloTarget.name",

    // Path of the composed value metric property that this time series represents.
    // Prometheus can only store single valued metrics. This is used to decompose
    // a multi-valued metric (i.e., an object) into multiple single values (see examples below).
    metric_prop_key="objPropKey"
}
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metricType is the snake case version of the respective ComposedMetricType.instance.metricTypeName. metricType can also be inferred from a MetricMapping CRD by using the snake case of <crd_api_group>_<crd_kind_without_metric_mapping_suffix>. For example:

// CRD:
apiVersion: metrics.polaris-slo-cloud.github.io/v1
kind: CostEfficiencyMetricMapping

// Prometheus time series name:
polaris_composed_metrics_polaris_slo_cloud_github_io_cost_efficiency
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Multi-valued composed metric example: Since Prometheus supports only a single floating point value per metric sample, we store the properties of a composed metric object using multiple samples and a classifier label. For example:

// Composed metric object:
{
    a: 100,
    b: {
        c: 1.1,
        d: 2.2,
    }
}

// Prometheus samples:
polaris_composed_example_metric{target_gvk="apps/v1/Deployment", target_namespace="default", target_name="test" metric_prop_key="a"} 100
polaris_composed_example_metric{target_gvk="apps/v1/Deployment", target_namespace="default", target_name="test" metric_prop_key="b.c"} 1.1
polaris_composed_example_metric{target_gvk="apps/v1/Deployment", target_namespace="default", target_name="test" metric_prop_key="b.d"} 2.2
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Single-valued composed metric example: Composed metrics that consist of a single value only use '.' as the prop_key.

polaris_composed_single_valued_metric{target_gvk="apps/v1/Deployment", target_namespace="default", target_name="test" metric_prop_key="."} 100
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