Correctly report single-step agent installations on Docker (#25472)

* Report single-step agent installations on Docker

* Add copyright notice

* Address a lint comment

* Address a review comment

* Finish addressing a review comment

comp/trace/config/install_signature.go

@@ -12,12 +12,15 @@ import (
 	"path/filepath"
 	"time"
 
+	"github.com/DataDog/datadog-agent/pkg/config/env"
 	"github.com/DataDog/datadog-agent/pkg/trace/config"
 	"github.com/google/uuid"
 )
 
 const (
-	defaultInstallType = "manual"
+	defaultInstallType          = "manual"
+	defaultDockerInstallType    = "docker_manual"
+	dockerSingleStepInstallType = "docker_single_step"
 )
 
 func applyOrCreateInstallSignature(c *config.AgentConfig) {
@@ -77,12 +80,22 @@ func generateNewInstallSignature(s *config.InstallSignatureConfig) (err error) {
 	}
 	*s = config.InstallSignatureConfig{
 		InstallID:   installID.String(),
-		InstallType: defaultInstallType,
+		InstallType: inferInstallTypeFromEnvironment(),
 		InstallTime: time.Now().Unix(),
 	}
 	return nil
 }
 
+func inferInstallTypeFromEnvironment() string {
+	if env.IsContainerized() {
+		if os.Getenv("DD_APM_ENABLED") != "" {
+			return dockerSingleStepInstallType
+		}
+		return defaultDockerInstallType
+	}
+	return defaultInstallType
+}
+
 func writeInstallSignatureToDisk(path string, s *config.InstallSignatureConfig) error {
 	contents, err := json.Marshal(s)
 	if err != nil {

comp/trace/config/install_signature_test.go

@@ -0,0 +1,35 @@
+// Unless explicitly stated otherwise all files in this repository are licensed
+// under the Apache License Version 2.0.
+// This product includes software developed at Datadog (https://www.datadoghq.com/).
+// Copyright 2024-present Datadog, Inc.
+
+package config
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestInferInstallTypeFromEnvironment(t *testing.T) {
+	t.Run("Non-dockerized agent", func(t *testing.T) {
+		assert.Equal(t, defaultInstallType, inferInstallTypeFromEnvironment())
+	})
+
+	t.Run("Dockerized manual instrumentation", func(t *testing.T) {
+		t.Setenv("DOCKER_DD_AGENT", "true")
+		assert.Equal(t, defaultDockerInstallType, inferInstallTypeFromEnvironment())
+	})
+
+	t.Run("Dockerized single-step instrumentation", func(t *testing.T) {
+		t.Setenv("DOCKER_DD_AGENT", "true")
+		t.Setenv("DD_APM_ENABLED", "true")
+		assert.Equal(t, dockerSingleStepInstallType, inferInstallTypeFromEnvironment())
+	})
+
+	t.Run("Non-standard environment variable values", func(t *testing.T) {
+		t.Setenv("DOCKER_DD_AGENT", "yes")
+		t.Setenv("DD_APM_ENABLED", "sure")
+		assert.Equal(t, dockerSingleStepInstallType, inferInstallTypeFromEnvironment())
+	})
+}