Enabling OpenTelemetry for a Scala Agent

The golem-otlp-exporter is a built-in plugin that exports agent telemetry (traces, logs, metrics) to any OTLP-compatible collector via OTLP/HTTP. No plugin installation is needed — just enable it in the application manifest.

Step 1 — Enable the Plugin in golem.yaml

Add the plugin to the component (or agent) that should emit telemetry:

components:
  my-app:service:
    plugins:
      - name: golem-otlp-exporter
        version: "1.5.8"
        parameters:
          endpoint: "http://localhost:4318"
          signals: "traces,logs,metrics"

Plugin Parameters

Step 2 — Deploy

golem deploy --yes

After deployment, newly created agents from this component automatically send telemetry to the configured collector.

What Gets Exported

Traces

Spans are created automatically for:

• Agent invocations
• RPC calls to other agents
• Outgoing HTTP requests

Trace and span IDs propagate from inbound HTTP requests (via code-first routes) and are included in outgoing HTTP request headers automatically.

Custom Spans

Use the ContextApi from the Scala SDK to create custom spans:

import golem.host.ContextApi
 
val span = ContextApi.startSpan("my-operation")
span.setAttribute("env", ContextApi.AttributeValue.StringValue("production"))
span.setAttributes(List(
  ContextApi.Attribute("service", ContextApi.AttributeValue.StringValue("my-service")),
  ContextApi.Attribute("version", ContextApi.AttributeValue.StringValue("1.0")),
))
 
// ... do work ...
 
val ctx = ContextApi.currentContext()
println(s"trace_id: ${ctx.traceId()}")
span.finish()

Logs

When logs is included in signals, all log output is forwarded to the OTLP collector. See the golem-logging-scala skill for full logging guidance.

import golem.wasi.Logging
 
println("Hello from Scala!")
Logging.debug("This is a debug log entry")

Metrics

When metrics is included in signals, exported metrics include the following non-exhaustive selection:

These are emitted OTLP names. A backend such as Prometheus may normalize dots to underscores and add suffixes; use that backend’s mapping when writing queries.

Each metric includes service.name, golem.agent.id, golem.component.id, and golem.component.version attributes.

Export Semantics

• Durable Start, End, and Cancelled metadata drives span lifecycle. Long-lived spans retain their origin trace across invocations; failed or retrying attempts do not prematurely close the logical span. Logs use their recorded trace context.
• Stream summaries use bounded event/outcome metric labels and aggregate item counts; they do not emit a span per item. Active resource and memory values are gauges, and metric labels avoid resource IDs and payload values.
• In agent-type service-name mode, service.name excludes constructor parameters and phantom instance IDs; golem.agent.id remains the full identity.
• Collector export is best effort. Accepted source state advances when a send fails, and traces, logs, and metrics are still attempted independently. Exactly-once plugin batch delivery is not exactly-once collector delivery.
• Fork/revert cannot retract telemetry already accepted by a collector. Source deletion does not provide a terminal signal, so no successful close is invented. Switching plugin instances can lose open-span state; continuity is deferred to GOL-667.

Local Observability Stack

The Golem repository includes a ready-made Docker Compose setup at docker-examples/otlp-collector/:

docker compose -f docker-examples/otlp-collector/docker-compose.yml up -d

This starts:

• OTel Collector on port 4318 (OTLP/HTTP)
• Jaeger on http://localhost:16686  (traces)
• Prometheus on http://localhost:9090  (metrics)
• Loki via Grafana (logs)
• Grafana on http://localhost:3000  (admin/admin)

Configure the plugin with endpoint: "http://localhost:4318" to use this stack.

Per-Environment Configuration

Use presets to vary the endpoint across environments:

components:
  my-app:service:
    plugins:
      - name: golem-otlp-exporter
        version: "1.5.8"
        parameters:
          endpoint: "http://localhost:4318"
          signals: "traces,logs,metrics"
    presets:
      app-env:production:
        pluginsMergeMode: replace
        plugins:
          - name: golem-otlp-exporter
            version: "1.5.8"
            parameters:
              endpoint: "https://otel.prod.example.com:4318"
              headers: "x-api-key={{ OTLP_API_KEY }}"
              signals: "traces,logs,metrics"

Key Points

• Built-in — no golem plugin register needed, just add to golem.yaml
• Deploy required — run golem deploy after adding the plugin configuration
• Trace context propagates automatically through HTTP routes and RPC calls
• Use ContextApi.startSpan from golem.host.ContextApi for custom spans
• Plugin can be activated/deactivated per agent with golem agent activate-plugin / golem agent deactivate-plugin

Related Guides

• Load golem-manage-plugins for the general plugin installation model (manifest sections, CLI commands, priority, per-environment configuration)