Add Kubernetes API coverage test consuming traces

It pulls a file from testdata with traces collected by Jaeger and then
iterates over them in order to group them into those which use the
contract interface, are known (and usually valid) uses outside of it.
Later it can further analyze the parameters used over the run of
Kubernetes conformance tests.

It requires patched Kubernetes
with:
AwesomePatrol/kubernetes@5a18a66
or at:
https://github.com/AwesomePatrol/kubernetes/tree/add-kubernetes-etcd-contract-tracker

Author: AwesomePatrol

tests/robustness/coverage/coverage_test.go

@@ -0,0 +1,139 @@
+// Copyright 2025 The etcd Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package coverage_test
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestInterfaceUse(t *testing.T) {
+	files, err := os.ReadDir("testdata")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	for _, file := range files {
+		filename := file.Name()
+		t.Run(filename, func(t *testing.T) { testInterfaceUse(t, filename) })
+	}
+}
+
+func testInterfaceUse(t *testing.T, filename string) {
+	b, err := os.ReadFile(filepath.Join("testdata", filename))
+	if err != nil {
+		t.Fatalf("read test data: %v", err)
+	}
+	var dump Dump
+	err = json.Unmarshal(b, &dump)
+	if err != nil {
+		t.Fatalf("unmarshal testdata %s: %v", filename, err)
+	}
+	traces, apiserverOnly, etcdOnly := filterOutIncomplete(dump)
+	if apiserverOnly > 0 {
+		t.Logf("WARNING: some traces are present in Apiserver only: %d > 0", apiserverOnly)
+	}
+	if etcdOnly > 0 {
+		t.Logf("WARNING: some traces are present in Etcd only: %d > 0", etcdOnly)
+	}
+
+	t.Run("interface_bypass", func(t *testing.T) {
+		var interfaceBypass []Trace
+		for _, trace := range traces {
+			if !isContractCall(trace) {
+				interfaceBypass = append(interfaceBypass, trace)
+			}
+		}
+		t.Logf("Traces which did not go through the interface: %d / %d", len(interfaceBypass), len(traces))
+
+		knownBypass := map[string]bool{
+			"etcdserverpb.Lease/LeaseGrant":   true, // Used to manage masterleases and events
+			"etcdserverpb.Maintenance/Status": true, // Used to expose database size on apiserver's metrics endpoint
+			"etcdserverpb.Watch/Watch":        true, // Not part of the contract interface (yet)
+			"etcdserverpb.KV/Compact":         true, // Compaction should move to using internal Etcd mechanism
+		}
+		bypassByOperationName := make(map[string]int)
+		for _, trace := range interfaceBypass {
+			for _, span := range trace.Spans {
+				if span.ServiceName != "etcd" {
+					continue
+				}
+				opName := span.OperationName
+				if opName == "etcdserverpb.KV/Txn" || opName == "etcdserverpb.KV/Range" {
+					// TODO: Associate etcdserverpb.KV/{Txn,Range}s with known operations:
+					// key == "/registry/health" -> healthcheck
+					// key == "compact_rev_key" -> compaction
+					// count_only -> count
+					// strings.Count(key, "/") == 2, limit == 1 -> consistent read
+					continue
+				}
+
+				bypassByOperationName[opName]++
+
+				// Print the first span to make it easier to troubleshoot the test.
+				if bypassByOperationName[opName] == 1 && !knownBypass[opName] {
+					t.Logf("%s: %+v", opName, span)
+				}
+			}
+		}
+		t.Logf("contract bypass count by operation: %+v", bypassByOperationName)
+		for op := range bypassByOperationName {
+			if !knownBypass[op] {
+				t.Errorf("operation not found in the set of known interface bypasses: %s", op)
+			}
+		}
+	})
+	t.Run("contract_methods_set_rev_when_needed", func(t *testing.T) {
+		for op, percentageWithRev := range map[string]float64{
+			"Get kubernetesEtcdContract":              0, // Conformance tests don't issue stale reads
+			"OptimisticPut kubernetesEtcdContract":    0.7,
+			"OptimisticDelete kubernetesEtcdContract": 1,
+			"List kubernetesEtcdContract":             0.8,
+		} {
+			t.Run(op, func(t *testing.T) {
+				operationSpans := make([]Span, 0, len(traces))
+				for _, trace := range traces {
+					for _, span := range trace.Spans {
+						if span.OperationName == op {
+							operationSpans = append(operationSpans, span)
+							break
+						}
+					}
+				}
+				t.Logf("Found %d traces matching %s operation", len(operationSpans), op)
+
+				result := map[string]int{
+					"unset":   0,
+					"set":     0,
+					"missing": 0, // absent in collected spans belonging to the trace
+				}
+				for _, span := range operationSpans {
+					result[revFromSpan(span)]++
+				}
+				t.Logf("Distribution of revision values: %+v", result)
+
+				if c := result["missing"]; c > 0 {
+					t.Errorf("some traces are missing revision tag, count=%d", c)
+				}
+				total := float64(len(operationSpans))
+				if share := float64(result["set"]) / total; share > percentageWithRev+0.2 || share < percentageWithRev-0.2 {
+					t.Errorf("expected rev>0 range calls %.2f to be close [±20%%] to %.2f", share, percentageWithRev)
+				}
+			})
+		}
+	})
+}

tests/robustness/coverage/helpers_test.go

@@ -0,0 +1,106 @@
+// Copyright 2025 The etcd Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package coverage_test
+
+import "strings"
+
+type Tag struct {
+	Key   string `json:"key"`
+	Type  string `json:"type"`
+	Value any    `json:"value"`
+}
+
+type Log struct {
+	Timestamp int64 `json:"timestamp"`
+	Fields    []Tag `json:"fields"`
+}
+
+type Span struct {
+	TraceID       string `json:"traceID"`
+	SpanID        string `json:"spanID"`
+	OperationName string `json:"operationName"`
+	Tags          []Tag  `json:"tags"`
+	ProcessID     string `json:"processID"`
+	Logs          []Log  `json:"logs"`
+	ServiceName   string
+}
+
+type Process struct {
+	ServiceName string `json:"serviceName"`
+}
+
+type Trace struct {
+	TraceID   string             `json:"traceID"`
+	Spans     []Span             `json:"spans"`
+	Processes map[string]Process `json:"processes"`
+}
+
+type Dump struct {
+	Data []Trace `json:"data"`
+}
+
+func filterOutIncomplete(dump Dump) (ret []Trace, apiserverOnly, etcdOnly int) {
+	// TODO: Make request directly to Jaeger (OTLP /api/v3) and use OTLP types
+	ret = make([]Trace, 0, len(dump.Data))
+	for _, trace := range dump.Data {
+		var associatedToEtcd, associatedToApiserver bool
+		for i := range trace.Spans {
+			span := &trace.Spans[i]
+			span.ServiceName = trace.Processes[span.ProcessID].ServiceName
+			if span.ServiceName == "etcd" {
+				associatedToEtcd = true
+			}
+			if span.ServiceName == "apiserver" {
+				associatedToApiserver = true
+			}
+		}
+		if !associatedToEtcd {
+			apiserverOnly++
+			continue
+		}
+		if !associatedToApiserver {
+			etcdOnly++
+			continue
+		}
+		ret = append(ret, trace)
+	}
+	return
+}
+
+func isContractCall(trace Trace) bool {
+	for _, span := range trace.Spans {
+		if strings.HasSuffix(span.OperationName, "kubernetesEtcdContract") {
+			return true
+		}
+	}
+	return false
+}
+
+func revFromSpan(span Span) string {
+	for _, tag := range span.Tags {
+		if tag.Key == "rev" {
+			if tag.Type != "int64" {
+				continue
+			}
+			if tag.Value.(float64) == 0 {
+				return "unset"
+			}
+			if tag.Value.(float64) > 0 {
+				return "set"
+			}
+		}
+	}
+	return "missing"
+}