# Signal to Metrics
### Description
This connector generates custom metrics from logs, metrics, and traces using OTTL expressions.
### Use
Use this connector to:
* Count log events as metrics for monitoring error rates or request frequencies
* Generate latency histograms from trace spans
* Derive new metrics from existing metric datapoints
* Build custom service level indicators from raw telemetry
### Supported Types
| Metrics | Logs | Traces |
| ------- | ---- | ------ |
| ✓ | ✓ | ✓ |
All input types produce metrics as output.
### Configuration
| Field | Description |
| ------------------ | ---------------------------------------------------------------------------------------------- |
| Telemetry Types | Select which signal types to process: Logs, Metrics, or Traces. At least one must be selected. |
| Metric Definitions | One or more metrics to generate. See metric definition fields below. |
#### Metric Definition
| Field | Description |
| ------------------- | ------------------------------------------------------------------------------------------------------------------------------ |
| Name | The metric name (e.g., `http.request.count`). |
| Description | Description of the metric. |
| Unit | Metric unit (e.g., `ms`, `bytes`, `logs`). |
| Type | `Sum`, `Gauge`, `Histogram`, or `Exponential Histogram`. |
| Value Expression | [OTTL expression ](#ottl-expressions)that returns the metric value. |
| Condition | OTTL condition to filter which signals generate this metric. |
| Buckets | Bucket boundaries (Histogram only). Default: `[2, 4, 6, 8, 10, 50, 100, 200, 400, 800, 1000, 1400, 2000, 5000, 10000, 15000]`. |
| Max Size | Max bucket count (Exponential Histogram only). Default: `160`. |
| Attributes | Attributes to include in the output metric. |
| Resource Attributes | Resource attributes to include in the output metric. |
#### Metric Types
| Type | Description |
| --------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Sum | Aggregates numeric values. Use for counters and cumulative metrics. |
| Gauge | Records the last observed value. Use for current state metrics. |
| Histogram | Distributes values across explicit buckets. Optionally configure `Buckets` (default: `[2, 4, 6, 8, 10, 50, 100, 200, 400, 800, 1000, 1400, 2000, 5000, 10000, 15000]`). |
| Exponential Histogram | Uses dynamic bucket sizing. Optionally configure `Max Size` (default: `160`). |
#### Attributes
Specify which attributes from the source signal to include in the output metric. If no attributes are defined, the output metric will have no attributes.
| Field | Description |
| ------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| Key | The attribute key to include. |
| Behavior | `Required` (default): incoming signals missing this attribute are skipped entirely. `Optional`: attribute is included if present on incoming signals, excluded if not. `Has Default`: use default value if attribute is missing from incoming signals. |
| Default Value | Value to use when attribute is missing (only with `Has Default`). |
#### Resource Attributes
Specify which resource attributes to include in the output metric. If no resource attributes are defined, **all** incoming resource attributes are included.
| Field | Description |
| ------------- | ---------------------------------------------------------------------------------------------------- |
| Key | The resource attribute key to include. |
| Behavior | `Optional` (default) or `Has Default`. Same behavior as attributes, but `Required` is not available. |
| Default Value | Value to use when attribute is missing (only with `Has Default`). |
#### Conditions
Filter which signals generate metrics using OTTL conditions.
Example conditions:
* `attributes["http.status_code"] >= 400` — only error responses
* `severity_number >= SEVERITY_NUMBER_ERROR` — only error logs
* `name == "HTTP GET"` — specific span names
#### OTTL Expressions
The connector supports [OTTL functions](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/pkg/ottl/ottlfuncs/README.md) for extracting values.
Common expressions:
* `1` — literal value for counting
* `Int(attributes["response_time"])` — extract integer attribute
* `Double(attributes["duration_ms"])` — extract float attribute
For spans, `AdjustedCount()` calculates accurate counts when sampling is enabled:
```
Int(AdjustedCount())
```
### Example Configuration(s)
#### Count Log Records by Severity
Count all log records, grouped by severity level.
* Signal Type: `logs`
* Name: `log.record.count`
* Type: `Sum`
* Value Expression: `1`
* Attributes: Key `severity`, Behavior `Optional`
#### HTTP Request Duration Histogram
Generate a latency histogram from HTTP server spans.
* Signal Type: `spans`
* Name: `http.server.duration`
* Unit: `ms`
* Type: `Histogram`
* Value Expression: `Double(attributes["http.server.request.duration"])`
* Condition: `kind == SPAN_KIND_SERVER`
* Buckets: `[5, 10, 25, 50, 100, 250, 500, 1000, 2500, 5000, 10000]`
* Attributes: Key `http.route`, Behavior `Optional`; Key `http.method`, Behavior `Required`
#### Error Count by Service
Count error logs grouped by service name.
* Signal Type: `logs`
* Name: `error.count`
* Type: `Sum`
* Value Expression: `1`
* Condition: `severity_number >= SEVERITY_NUMBER_ERROR`
* Resource Attributes: Key `service.name`, Behavior `Optional`
#### Span Count with Sampling Adjustment
Accurately count spans when sampling is enabled.
* Signal Type: `spans`
* Name: `span.count`
* Type: `Sum`
* Value: `Int(AdjustedCount())`
### Technical Notes
The connector automatically adds `signaltometrics.service.instance.id` to every output metric for single-writer compliance.
The connector does not perform time-based aggregation. Metrics are aggregated per batch only.
### Related Resources
* [OTTL Syntax Reference](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/pkg/ottl/README.md)
* [OTTL Functions](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/pkg/ottl/ottlfuncs/README.md)
* [OTEL Signal to Metrics Documentation](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/connector/signaltometricsconnector/README.md)
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