Transforming Metrics through Code Rules

OTLP Metric Code Rule Examples

Here are common patterns to help you enrich, clean, or modify incoming OTLP-formatted metrics.

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1. Add Custom Attribute to All Gauge Metrics

const u = ascent.decode.unflatten(Event);

u.resourceMetrics.forEach((rm) => {
    rm.scopeMetrics.forEach((sm) => {
        sm.metrics.forEach((m) => {
            if (m.gauge) {
                m.gauge.dataPoints.forEach((dp) => {
                    dp.attributes ||= [];
                    dp.attributes.push({
                        key: "env",
                        value: { stringValue: "prod" }
                    });
                });
            }
        });
    });
});

Event = ascent.encode.flatten(u);

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🧹2. Drop Metric by Name

Drop all metrics with the name http_requests_unwanted.

const u = ascent.decode.unflatten(Event);

u.resourceMetrics.forEach((rm) => {
    rm.scopeMetrics.forEach((sm) => {
        sm.metrics = sm.metrics.filter(m => m.name !== "http_requests_unwanted");
    });
});

Event = ascent.encode.flatten(u);

---

3. Rename Metric

Rename latency_ms to request_duration_ms.

const u = ascent.decode.unflatten(Event);

u.resourceMetrics.forEach((rm) => {
    rm.scopeMetrics.forEach((sm) => {
        sm.metrics.forEach((m) => {
            if (m.name === "latency_ms") {
                m.name = "request_duration_ms";
            }
        });
    });
});

Event = ascent.encode.flatten(u);

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4. Convert Gauge to Sum

Convert a gauge to a sum with cumulative aggregation.

const u = ascent.decode.unflatten(Event);

u.resourceMetrics.forEach((rm) => {
    rm.scopeMetrics.forEach((sm) => {
        sm.metrics.forEach((m) => {
            if (m.gauge) {
                m.sum = {
                    dataPoints: m.gauge.dataPoints,
                    aggregationTemporality: 2,  // CUMULATIVE
                    isMonotonic: false
                };
                delete m.gauge;
            }
        });
    });
});

Event = ascent.encode.flatten(u);

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5. Filter Out Data Points by Value

Only keep gauge datapoints where value > 0.

const u = ascent.decode.unflatten(Event);

u.resourceMetrics.forEach((rm) => {
    rm.scopeMetrics.forEach((sm) => {
        sm.metrics.forEach((m) => {
            if (m.gauge) {
                m.gauge.dataPoints = m.gauge.dataPoints.filter(dp => dp.asDouble > 0);
            }
        });
    });
});

Event = ascent.encode.flatten(u);

---

6. Tag Metrics Based on Name

Add a type: db attribute if metric name contains sql.

const u = ascent.decode.unflatten(Event);

u.resourceMetrics.forEach((rm) => {
    rm.scopeMetrics.forEach((sm) => {
        sm.metrics.forEach((m) => {
            if (m.name.includes("sql")) {
                (m.gauge?.dataPoints || []).forEach((dp) => {
                    dp.attributes ||= [];
                    dp.attributes.push({
                        key: "type",
                        value: { stringValue: "db" }
                    });
                });
            }
        });
    });
});

Event = ascent.encode.flatten(u);

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Tips

• Always wrap transformations in a try/catch if you're unsure about event structure.

• You can modify resource.attributes, scope.name, or any part of the OTLP model.