otel-ottl

OpenTelemetry Transformation Language (OTTL)

Components that use OTTL

OTTL is not limited to the transform and filter processors. Processors (transform, filter, tailsampling, logdedup) and connectors (routing, count, sum, signaltometrics) accept OTTL expressions. See components for the full list with use cases.

OTTL syntax

Path expressions

Navigate telemetry data using dot notation:

span.name
span.attributes["http.method"]
resource.attributes["service.name"]

Contexts (first path segment): resource, scope, span, spanevent, metric, datapoint, log.

Enumerations

Use int64 constants for enumeration fields:

span.status.code == STATUS_CODE_ERROR
span.kind == SPAN_KIND_SERVER

Operators

Assignment: = — Comparison: ==, !=, >, <, >=, <= — Logical: and, or, not

Functions

Converters (uppercase, return values):

ToUpperCase(span.attributes["http.request.method"])
Substring(log.body.string, 0, 1024)
Concat(["prefix", span.attributes["request.id"]], "-")
IsMatch(metric.name, "^k8s\\..*$")

Editors (lowercase, modify data in-place):

set(span.attributes["region"], "us-east-1")
delete_key(resource.attributes, "internal.key")
limit(log.attributes, 10, [])

See function-reference for the full list of editors and converters.

Conditional statements

Use where to apply transformations conditionally:

span.attributes["db.statement"] = "REDACTED" where resource.attributes["service.name"] == "accounting"

Nil checks

Use nil for absence checking (not null):

resource.attributes["service.name"] != nil

Validation workflow

1. Validate config syntax — run otelcol validate --config=config.yaml to catch compilation errors before starting the Collector.
2. Test with the debug exporter — route transformed telemetry to a debug exporter and inspect the output:

exporters:
  debug:
    verbosity: detailed

service:
  pipelines:
    traces:
      receivers: [otlp]
      processors: [transform]
      exporters: [debug]   # swap in production exporter once validated