Opentelemetry

OpenTelemetry Operational Guide

Concise operational pointers for deep OpenTelemetry SDK and Collector troubleshooting and tuning.

Assumes you already know what traces/metrics/logs are, what a span is, and that propagation carries context across services. This skill covers the operational layer — the parts models tend to gloss over: propagator selection in mixed fleets, sampling design, semantic-convention stability, collector pipeline ordering, OTLP transport quirks, instrumentation-library upgrade pain, and cardinality cost control.

When to use

Load when the question is about:

• Propagator selection across mixed Zipkin/Jaeger/W3C fleets (OTEL_PROPAGATORS)
• Head-based vs tail-based sampling design and the load-balancing-exporter pattern
• Semantic-convention stability levels and the HTTP migration (OTEL_SEMCONV_STABILITY_OPT_IN)
• Collector pipeline ordering (memory_limiter first, batch last)
• Collector deployment topology (agent / sidecar / gateway / coordinator+sampler)
• OTLP transport mismatches (4317 gRPC vs 4318 HTTP, protocol/port pairing)
• Resource auto-detection and service.name = unknown_service diagnosis
• Instrumentation-library version compatibility, duplicate-span pollution
• Metric cardinality control via Views API and exemplar-based high-cardinality offload
• Span lifecycle bugs (forgotten End(), mutations after end, orphan parents)
• Logs bridge into log4j/logback/slog/python-logging with trace_id/span_id injection
• Histogram choice (explicit-bucket vs base-2 exponential)

Do NOT load for: explaining what tracing is, picking a backend, first-time install, basic span-creation tutorials, or "show me a Grafana dashboard."

Three signals: SDKs and resource layer

• Three independent data models, three SDKs: TracerProvider, MeterProvider, LoggerProvider. They share Resource and propagation context but otherwise evolve on independent stability tracks. Trace SDK is stable; Metric SDK stable since 1.x; Log SDK stable for the bridge surface, individual log appenders still vary.
• Resource = process-level identity, attached to every signal. service.name is REQUIRED by spec; missing it → SDKs fall back to literal unknown_service (or unknown_service:python, etc.). Spans bucket under that string in every backend.
• Set service.name by precedence: OTEL_SERVICE_NAME env (highest), OTEL_RESOURCE_ATTRIBUTES=service.name=foo, programmatic Resource.builder().put("service.name", ...), then SDK default.
• Other recommended resource attrs: service.version, service.namespace, service.instance.id, deployment.environment.name (renamed from deployment.environment in newer semconv).
• Auto-detection: SDKs ship resource detectors for host.id, host.name, os.type, process.pid, process.runtime.*, container.id (parsed from /proc/self/cgroup). Kubernetes attrs (k8s.pod.name, k8s.namespace.name, k8s.node.name) come from either: (a) Downward API → OTEL_RESOURCE_ATTRIBUTES, or (b) the k8sattributes collector processor enriching at the gateway. Prefer the collector path — survives missing pod-spec env vars.

Propagators

• Default since spec 1.0: tracecontext,baggage (W3C). traceparent: 00-{trace_id_32hex}-{span_id_16hex}-{flags_2hex} plus tracestate for vendor-specific add-ons. Only the W3C TraceContext Level 2 random-flag is required for consistent probability sampling.
• OTEL_PROPAGATORS is comma-separated and order matters for injection (the first propagator that matches on extract wins; all are written on inject). Known values: tracecontext, baggage, b3 (single header), b3multi (X-B3-TraceId/X-B3-SpanId/X-B3-Sampled), jaeger (uber-trace-id, deprecated), xray (third-party), ottrace (deprecated), none.
• Mixed fleet rule: if you're migrating in from a Zipkin-instrumented service, set OTEL_PROPAGATORS=tracecontext,baggage,b3multi. New services emit W3C; old services keep working. Drop b3multi only after the last B3 emitter is gone.
• Baggage (baggage header): cross-cutting key-value, propagated alongside trace context. W3C cap: 8192 bytes total, 64 list-members; OpenTelemetry Python enforces 4096 per value, 180 entries. Excess silently dropped on inject — no error.
• DO NOT put PII / credentials / API keys in baggage. Auto-instrumentation forwards baggage on every outbound HTTP — including to third parties. Strip in egress middleware if you must carry sensitive context internally.
• Baggage ≠ span attributes: baggage doesn't auto-attach to spans. To turn baggage into attributes, use the baggage SDK span processor (Java/Python) or a transform collector processor.
• Sampling decision propagates via traceparent flags byte (01 = sampled). If a parent service samples-out (flags=00), all downstream services inherit "not sampled" under ParentBased — child AlwaysOn doesn't override, by design.

Sampling: head- vs tail-based

Head-based — decision at span start, in the SDK:

• AlwaysOn / AlwaysOff — trivial.
• TraceIdRatioBased(0.1) — deterministic hash of trace_id, 10% of traces. Same trace_id = same decision across services (consistent).
• ParentBased(root=TraceIdRatioBased(0.1)) — default in most SDKs. If parent context exists, follow parent's sampled flag. Otherwise apply root sampler. Prevents partial traces.
• OTEL_TRACES_SAMPLER defaults to parentbased_always_on; for ratio sampling set OTEL_TRACES_SAMPLER=parentbased_traceidratio and OTEL_TRACES_SAMPLER_ARG=0.1.
• W3C TraceContext Level 2 + OTEP 235 consistent probability sampling: SDKs encode the sampling threshold in tracestate (ot=th:...) so downstream collectors / backends know the effective rate without re-deriving it. Required for accurate rate analytics under sampling. Adoption is rolling out per-SDK in 2025/2026.

Tail-based — decision after the trace completes, in the collector:

• tail_sampling processor (in opentelemetry-collector-contrib). Buffers all spans of a trace for decision_wait (default 30s), then evaluates policies:
  • latency (p95 > N ms), status_code (ERROR), string_attribute (e.g. tenant), numeric_attribute, rate_limiting (spans/sec), probabilistic, composite (AND/OR of policies).
• Hard requirement: all spans of one trace MUST land at the same collector instance. A multi-replica collector behind a normal LB will split the trace and each replica makes a different decision → broken/missing spans.

Coordinator+sampler topology (canonical): two-tier collector deployment.

1. Tier 1 (coordinator/router): receives OTLP, applies the loadbalancing exporter with routing_key: traceID, resolver: dns (Kubernetes headless service) or static. Hashes trace_id → routes to a fixed Tier-2 replica.
2. Tier 2 (sampler): runs the tail_sampling processor. Stateful — sticky per trace_id.

• Without this topology, sharing trace state across collector pods would require external storage. The load-balancer is cheaper.
• loadbalancing exporter routing keys: traceID (default for traces), service (default for metrics), streamID for logs, resource for resource-grouped routing.
• Watch otelcol_loadbalancer_num_backends — if it doesn't match expected replicas, DNS hasn't converged or readiness is stuck.

Semantic conventions

The contract between instrumentation and backends. Stability matters or your dashboards break on SDK upgrade.

• Stability levels: development (was experimental) → alpha → beta → release_candidate → stable. Only stable is a breaking-change-protected contract. Default is development if unset.
• Stable in 2024+: HTTP (spans + metrics), database (partial), system metrics. In flight: gen-ai, RPC, messaging, k8s. Check semantic-conventions/model/<area> stability: field before depending.
• HTTP migration (the canonical one): http.method → http.request.method, http.status_code → http.response.status_code, http.url → url.full, http.host → server.address + server.port, http.scheme → url.scheme, http.target → url.path + url.query, net.peer.name → server.address. Span name template changed to {method} {http.route} (e.g. GET /users/:id).
• OTEL_SEMCONV_STABILITY_OPT_IN controls instrumentation library output: http (new only), http/dup (both old and new — for migration windows), unset (old only, deprecated). Per-domain comma-list possible (http,db).
• Other stable attribute clusters: db.system.name (was db.system), db.namespace, db.query.text (was db.statement), messaging.system, messaging.destination.name, messaging.operation.type, rpc.system, rpc.service, rpc.method, network.peer.address, network.peer.port, network.protocol.name.
• Span name discipline: low-cardinality. GET /users/:id (route template) — NOT GET /users/12345. Raw URLs in span name → metrics-from-spans (RED) explode.

OTLP exporter and ports

• OTLP/gRPC default port: 4317. OTLP/HTTP default port: 4318. This is the single most common misconfiguration.
• Endpoints differ by protocol:
  • gRPC: just http://collector:4317 (no path, the gRPC service name is in the proto).
  • HTTP: append /v1/traces, /v1/metrics, /v1/logs. SDKs append automatically when given a base URL only for HTTP, and only on OTEL_EXPORTER_OTLP_ENDPOINT, not on signal-specific overrides like OTEL_EXPORTER_OTLP_TRACES_ENDPOINT (which is treated as the full URL including path).
• OTEL_EXPORTER_OTLP_PROTOCOL: grpc (default), http/protobuf, http/json. Mismatch with collector port = silent connection refused or 404. Pointing gRPC at 4318 → "transport closed" / UNAVAILABLE. Pointing HTTP at 4317 → handshake failure or "Method Not Allowed" / 405.
• Receivers can multiplex by Content-Type if both protocols listen on the same port — the collector OTLP receiver supports this when both protocols.grpc and protocols.http are configured. Standard receiver YAML still binds 4317 + 4318 separately; multiplexing requires explicit shared bind.
• Headers (OTEL_EXPORTER_OTLP_HEADERS=key=val,key2=val2) — comma-separated, URL-encoded values. SaaS backends use this for API keys.
• Compression: OTEL_EXPORTER_OTLP_COMPRESSION=gzip. ~5-10× payload reduction on traces; cheap CPU cost; turn on by default.
• Batch span processor knobs: OTEL_BSP_SCHEDULE_DELAY=5000 (ms between exports), OTEL_BSP_MAX_QUEUE_SIZE=2048, OTEL_BSP_MAX_EXPORT_BATCH_SIZE=512. High span rate + small queue = drops with BatchSpanProcessor warnings; raise queue or shorten delay.

Collector pipeline ordering

Pipelines are per-signal. Order of processors matters semantically:

receivers:
  otlp:
    protocols: { grpc: { endpoint: 0.0.0.0:4317 }, http: { endpoint: 0.0.0.0:4318 } }
processors:
  memory_limiter:
    check_interval: 1s
    limit_mib: 4000
    spike_limit_mib: 800
  k8sattributes: {}    # gateway only
  resource: { attributes: [{ key: deployment.environment.name, value: prod, action: upsert }] }
  tail_sampling: { decision_wait: 30s, policies: [...] }
  batch: { timeout: 10s, send_batch_size: 8192 }
exporters:
  otlp/tempo: { endpoint: tempo:4317, tls: { insecure: true } }
service:
  pipelines:
    traces: { receivers: [otlp], processors: [memory_limiter, k8sattributes, resource, tail_sampling, batch], exporters: [otlp/tempo] }

• memory_limiter MUST be first. Applies backpressure at the receiver before any allocation downstream. Without it, a burst → OOM kill → data loss > a controlled drop.
  • limit_mib: hard cap. spike_limit_mib: distance below limit_mib at which soft refusal starts (default 20% of limit_mib).
  • Also set GOMEMLIMIT=80%-of-container-limit env var — Go runtime cooperates with the soft limit.
• batch MUST be last in the processor chain. Batching before sampling/dropping wastes work batching data that gets discarded.
• Sampling processors before batch, after memory_limiter. Tail sampling's buffering is its own memory pressure — memory_limiter first protects against it.
• k8sattributes processor enriches with pod metadata via Kubernetes API. Place after memory_limiter, before any processor that depends on those attrs. Needs RBAC — pods get/list/watch, optionally replicasets and deployments.
• Pipelines per signal: service.pipelines.traces, .metrics, .logs. A processor configured but not referenced in any pipeline silently doesn't run.

Collector deployment topology

Three patterns, often combined:

• Agent (DaemonSet): one collector pod per K8s node. SDKs send to $NODE_IP:4317. Wins: low latency, no network egress per app, scales 1:1 with nodes. Use for receiving + batching + minor enrichment, then forward upstream.
• Sidecar: one collector container per app pod. Wins: per-pod isolation, app-tied lifecycle. Costs: 1× collector overhead per pod. Use only when DaemonSet doesn't fit (multi-tenant clusters, app-specific scrape config).
• Gateway (Deployment): centralized collector replica set behind a service. Wins: tail sampling, fan-out to multiple backends, central policy. Receives from agents over OTLP. Run with HPA + the coordinator/sampler split if doing tail sampling.
• Hybrid (canonical for prod): Agent (DaemonSet) → Gateway-coordinator → Gateway-sampler. Each tier owns one concern.

Span lifecycle

• Start → set attributes/events/status → End. After End(), the span is immutable; mutations are silently dropped. Set RecordException and SetStatus(Error) before End.
• Forgotten End() = SDK memory leak. Span object stays in the active-set, never reaches BatchSpanProcessor. Use language idioms: Go defer span.End(), Python with tracer.start_as_current_span(...), Java try-with-resources on Scope, Node.js tracer.startActiveSpan(name, span => {...; span.end()}).
• Span events: structured timestamped key-value records attached to a span. Cheaper than separate logs for low-frequency in-context detail (e.g., "cache miss"). The Span Events API is being deprecated in favor of bridging to Logs (2026 announcement) — new code should use the Logs SDK with span context instead.
• Span links: relate spans across traces (async producer/consumer, batch-job processing N upstream traces). Carry context without parent-child relationship. Use when one span legitimately corresponds to many trace_ids.
• Span status: Unset (default), Ok, Error (with description). Unset is correct for non-errors — instrumentation should NOT pre-set Ok. Backends interpret Error distinctively.
• Orphan span: child ends after parent already exported (parent's BatchSpanProcessor flushed). The child still emits but its parent reference points to a span the backend has already stored — usually fine for trace assembly, but if parent and child go to different collectors during routing, the child can lose the parent. Tail-sampling decision_wait must be longer than the longest realistic span gap.

Auto-instrumentation per-language

• Go is the outlier: no runtime bytecode rewrite is possible on compiled binaries, so the OTel project ships an eBPF agent (Beta as of 2025) that hooks net/http, database/sql, gRPC, kafka-go. Runs as sidecar with CAP_SYS_ADMIN / CAP_BPF. For most teams: stick with manual instrumentation via otelhttp, otelgrpc, otelpgx.
• Operator (opentelemetry-operator) auto-injects per-language agents into pods via Instrumentation CRD + pod annotations (instrumentation.opentelemetry.io/inject-java=true). Sets JAVA_TOOL_OPTIONS / PYTHONPATH / NODE_OPTIONS — collides with user-set values in the same env vars (known issue; precedence is manifest > injected).
• Duplicate-span pitfall: HTTP-server framework (Express, Spring, Flask) auto-instruments AND the underlying HTTP library (Node http, Servlet, WSGI) auto-instruments → two spans per request, parent-child or sibling depending on hook depth. Disable one — usually the lower-level library — via per-instrumentation env (OTEL_PYTHON_DISABLED_INSTRUMENTATIONS=urllib3) or disable in code at SDK init.
• Instrumentation library version bounds: each opentelemetry-instrumentation-<lib> declares supported library version range (e.g., opentelemetry-instrumentation-flask >=1.0,<4.0). Mismatch silently degrades (no spans) or breaks startup with import errors. Pin in lockfile; check the contrib repo's per-instrumentation README for current bounds.

Metrics: instrument types and cardinality control

• Synchronous: Counter (monotonic up), UpDownCounter (signed), Histogram (distribution), Gauge (synchronous Gauge added 1.30+; previously only Observable).
• Asynchronous (callback-driven): ObservableCounter, ObservableUpDownCounter, ObservableGauge. SDK calls back at collection time. Use for sampling external state (queue depth, DB connection count).
• Histograms:
  • Explicit-bucket: legacy default. Buckets are static, must be tuned per-metric. Cross-instance aggregation requires identical bucket boundaries (string-encoded le labels).
  • Base-2 exponential (OTel-native, since spec 1.x): scale parameter auto-adjusts. Far better cross-instance aggregation, no bucket-mismatch silent drops, smaller wire size for high-resolution distributions. Default in newer SDKs (Java since 2.x, .NET since 1.9, Python defaults still explicit unless View overrides). Prefer.
• Cardinality control via the Views API (SDK-level, before export):

  view = View(
      instrument_type=Counter,
      instrument_name="http.server.request.count",
      attribute_keys=["http.method", "http.response.status_code"],  # drop everything else
  )
  

  • attribute_keys whitelist drops all other attributes at the SDK boundary — backend sees only listed keys. Single biggest cardinality lever.
  • Views can also rename instruments, change aggregation (force exponential histogram), or drop instruments entirely.
• Cardinality bombs in metrics: user_id, trace_id, request_id, session_id, raw URL paths, K8s pod names with random suffix → series count explodes. Bound aggregate metrics with cardinality-safe attrs only; use exemplars (next section) to reach the high-cardinality detail.
• Common metrics SDK env vars: OTEL_METRICS_EXPORTER=otlp|prometheus|console|none, OTEL_METRIC_EXPORT_INTERVAL=60000 (ms), OTEL_METRIC_EXPORT_TIMEOUT=30000.

Exemplars (metrics ↔ traces bridge)

• Exemplar: a (value, trace_id, span_id, timestamp, attributes) tuple attached to a histogram bucket / counter point. Lets users jump from a metric to one representative trace.
• OTEL_METRICS_EXEMPLAR_FILTER: trace_based (default — only emit when in active sampled span context), always_on, always_off.
• Histogram only on Prometheus — Prometheus exemplar API attaches to histogram buckets. Counters carry exemplars in OTLP but most query layers (PromQL via Prom-OTLP receiver) only surface histogram exemplars.
• Prometheus side: --enable-feature=exemplar-storage flag. Fixed-size in-memory ring buffer per series.
• The cardinality-control idiom: keep metric labels low-cardinality (status_class, method); for the high-cardinality dimension (user_id, customer), record on the trace, link via exemplar. Cardinality stays bounded; high-cardinality detail is reachable on demand.

Logs bridge

OpenTelemetry's logs story is a bridge from existing loggers to the OTel data model — not a new logging API. Use the existing logger.

• Java: OpenTelemetryAppender for log4j2 / logback. The javaagent auto-bridges. MDC is auto-populated with trace_id, span_id, trace_flags for the active span — reference in pattern as %X{trace_id}. Log file then carries the trace pointer.
• Python: LoggingHandler from opentelemetry-sdk._logs; or OTEL_PYTHON_LOG_CORRELATION=true injects via the LoggingInstrumentor to add otelTraceID/otelSpanID to the standard logging record's extra.
• Go: go.opentelemetry.io/contrib/bridges/otelslog for log/slog; otelzap for zap. Bridge wraps a logger and injects context.
• Node.js: bridges for Winston, Pino, Bunyan in @opentelemetry/instrumentation-<logger>.
• OTEL_LOGS_EXPORTER: otlp (default), console, none. Logs SDK is stable, but coverage of language-native logger bridges still varies.
• Pitfall: enabling the Python LoggingInstrumentor AND the LoggingHandler simultaneously double-emits — one writes to stdout, one writes via OTLP. Pick the path your collector pipeline expects.

Common pitfalls (consolidated)

• service.name unset → spans bucketed as unknown_service. Set OTEL_SERVICE_NAME in every container.
• OTEL_EXPORTER_OTLP_PROTOCOL=grpc against port 4318 → connection refused. HTTP against 4317 → 405.
• OTEL_EXPORTER_OTLP_TRACES_ENDPOINT is treated as the full URL including signal path; setting it to https://collector:4318 (no /v1/traces) breaks HTTP exports while leaving OTEL_EXPORTER_OTLP_ENDPOINT working — base vs override paths differ.
• Tail sampling without the loadbalancing exporter coordinator → split decisions, missing spans. Trace assembly looks fine in some traces, broken in others.
• tail_sampling.decision_wait shorter than your slowest span → decisions made on partial trace, late spans dropped.
• memory_limiter placed after batch → OOM kill before backpressure activates; data loss instead of controlled drop.
• Auto-instrumentation enabled at framework AND library level → duplicate spans, broken parent-child chain.
• OTEL_SEMCONV_STABILITY_OPT_IN unset on a deprecated instrumentation → still emits http.method etc.; new dashboards keyed on http.request.method show empty.
• OTEL_PROPAGATORS=tracecontext only, talking to a Zipkin/B3 service → context drops at the boundary, child spans get new trace_id (broken trace).
• High-cardinality metric attribute (user_id) → series count blows up at backend, cost/perf cliff. Use Views to drop, exemplars to reach.
• Span ended after parent already exported → orphan; parent reference dangles. In tail sampling, child can land on a different sampler replica if loadbalancing routing key isn't traceID.
• PII in baggage → leaks to every downstream HTTP, including third-party APIs (auto-instrumentation forwards by default).
• OTEL_BSP_MAX_QUEUE_SIZE too small under burst → BatchSpanProcessor queue full warnings + dropped spans. Raise queue OR shorten OTEL_BSP_SCHEDULE_DELAY.
• Forgetting defer span.End() (or equivalent) on early-return paths → SDK memory grows, eventually OOM.

Authoritative references

Specification (opentelemetry.io/docs/specs/otel):

• SDK environment variables
• Trace SDK
• Metrics SDK
• OTLP Protocol
• Propagators API
• Probability sampling (TraceState)
• Versioning and stability

Semantic conventions (github.com/open-telemetry/semantic-conventions):

• HTTP migration guide
• HTTP spans
• Group stability levels
• Resources
• Releases

Collector (opentelemetry.io/docs/collector and github.com/open-telemetry/opentelemetry-collector-contrib):

• Collector configuration
• Memory limiter processor
• Batch processor
• Tail-sampling processor
• Load-balancing exporter
• k8sattributes processor
• Gateway deployment
• Scaling the collector

Sampling and instrumentation guides:

• Tail sampling blog
• HTTP semantic conventions stable announcement
• Sampling milestones (2025)
• Stability proposal (2025)
• Go eBPF auto-instrumentation Beta
• Java agent

Operator and Kubernetes:

• opentelemetry-operator
• Auto-instrumentation injection
• k8s metadata enrichment blog

Reliable authors: Ted Young, Steve Flanders (Splunk/OTel governance); Tyler Yahn, Jacob Aronoff (collector core); Trask Stalnaker (Java instrumentation lead); Daniel Dyla (JS); Lightstep / ServiceNow / Honeycomb / Grafana Labs OTel blogs.

Guardrails

Before recommending a non-trivial OTel change (sampler, propagator list, processor order, OTLP protocol switch, semconv migration):

1. Quote the specific env var or config key and its default.
2. Cite the upstream doc — opentelemetry.io/docs/specs/otel, the contrib README for the processor/exporter, or github.com/open-telemetry/semantic-conventions at a pinned version.
3. Make the recommendation conditional on observed signals — span drop rate, collector memory, tail-sampling decision_wait overflow, unknown_service count, sampler effective rate — never blanket-tune.
4. Name a rollback: "if X spikes, revert by Y."
5. For semconv migration, always go through http/dup (or per-domain dup) for one release window — never flip atomically while dashboards are live.

Tuning without measurement is worse than defaults. Sampling rates, batch sizes, memory limits, and propagator order are environment-specific — a 1% sample that's correct for a 10k-RPS service is invisible at 10 RPS, and a propagator list that works in a homogeneous OTel fleet drops trace context the day a B3-emitting service joins.