Send needle's traces to the box's collector

k8s/needle/kustomization.yaml

@@ -140,6 +140,21 @@ configMapGenerator:
       # which is the only reason the per-peer lock contention was ever visible.
       - NEEDLE_PPROF=true
 
+      # Traces (ipni/infra#163), to the trace collector on the box's loopback
+      # (ipni/infra kubernetes/platform/alloy-traces) over OTLP/HTTP. Under
+      # hostNetwork this is the HOST's loopback, which is where it listens.
+      # Setting the endpoint alone is enough for needle to export.
+      - OTEL_EXPORTER_OTLP_ENDPOINT=http://127.0.0.1:4318
+
+      # Join the trace Envoy starts and follow its sampling decision (5%, see
+      # tracing in k8s/route-origin/envoy.yaml.j2) rather than deciding again.
+      # Safe only because needle is reachable solely through that Envoy: the
+      # API is loopback-only, and Envoy drops a client's traceparent and
+      # tracestate before reading them, so a client cannot choose what needle
+      # samples. NEEDLE_SAMPLING_FRACTION stays at its default of 0, so a
+      # request without a traceparent, from a tool on the box, is not traced.
+      - NEEDLE_TRACING_TRUST_TRACEPARENT=true
+
       # The libp2p resource manager defaults to 85% of HOST RAM and ignores the
       # cgroup limit, which would let it plan past the pod's 21Gi and get
       # OOM-killed. 16 GiB, in bytes: a quarter of the 64 GiB the single

k8s/route-origin/envoy.yaml.j2

@@ -87,10 +87,10 @@ static_resources:
                 # request and, with spawn_upstream_span, one for the call to
                 # needle (which instance, how long). The span names are the
                 # route decorators below, never the path: a path carries a CID,
-                # and every span name becomes a metric series. needle does not
-                # join these traces yet: v1.0.0 drops the traceparent Envoy
-                # sends (NEEDLE_TRACING_AUTH is unset), and its own sampling
-                # never fires (ipni/infra#163).
+                # and every span name becomes a metric series. needle joins
+                # these traces: it trusts the traceparent Envoy sends
+                # (NEEDLE_TRACING_TRUST_TRACEPARENT in k8s/needle), so it samples
+                # exactly these requests and adds its own spans below them.
                 #
                 # Only this sampling decides. A client cannot ask to be traced:
                 # client_sampling ignores x-client-trace-id, and the early