feat: wire structured logger (slog) throughout detection pipeline (#16)

## What and Why ?
Address pending `TODO` related to structured logging - Replaces
`log.Printf` calls with structured logging using Go's `log/slog`
package. Adds logger fields to detector, inventory, and EOL provider
components with consistent nil-safe defaults.

### Changes
- **Detectors**: Add `logger` field to EKS and Aurora detectors
- **Inventory**: Add `logger` parameter to Wiz inventory sources (EKS,
Aurora, ElastiCache) and parsing helpers
- **EOL Provider**: Add `logger` field to endoflife.date provider with
warning logs for skipped cycles
- **Main**: Initialize JSON logger at startup and wire through all
components
- **Tests**: Update all test constructors to pass `nil` logger (uses
`slog.Default()`)

### Benefits
- Structured JSON logging for production observability
- Context-aware log messages with typed fields
- Consistent logging pattern across codebase
- All TODO comments for logging addressed

All tests pass ✅

Author: Kiran01bm

.gitignore

@@ -1,5 +1,6 @@
 # Binaries
 bin/
+server
 *.exe
 *.dll
 *.so

ARCHITECTURE.md

@@ -624,7 +624,21 @@ make run-locally  # One-shot
 ### Monitoring
 
 - **Metrics**: Expose Prometheus metrics from gRPC service
-- **Logs**: Structured JSON logging
+- **Logs**: Structured JSON logging via `log/slog`
+  - Machine-readable JSON format for log aggregation tools (Datadog, Splunk, CloudWatch Insights)
+  - Context-aware logging with typed fields for queryable log data
+  - Configurable log levels (Info/Debug via `--verbose` flag)
+  - All components (detectors, inventory sources, EOL providers) use structured logging
+  - Example log entry:
+    ```json
+    {
+      "time": "2024-01-15T10:30:45Z",
+      "level": "WARN",
+      "msg": "failed to parse resource from CSV row",
+      "row_number": 42,
+      "error": "missing ARN"
+    }
+    ```
 - **Alerts**: Based on RED/YELLOW finding counts
 - **Dashboards**: Query gRPC API for real-time data
 

README.md

@@ -205,6 +205,7 @@ Version Guard is configured via environment variables or CLI flags:
 | `TAG_APP_KEYS` | Comma-separated AWS tag keys for app/service | `app,application,service` |
 | `TAG_ENV_KEYS` | Comma-separated AWS tag keys for environment | `environment,env` |
 | `TAG_BRAND_KEYS` | Comma-separated AWS tag keys for brand/business unit | `brand` |
+| `--verbose` / `-v` | Enable debug-level logging | `false` |
 
 **Customizing AWS Tag Keys:**
 
@@ -220,6 +221,36 @@ export TAG_APP_KEYS="team,squad,application"
 
 The tag keys are tried in order — the first matching tag wins.
 
+**Logging:**
+
+Version Guard uses structured JSON logging via Go's `log/slog` package for production observability:
+
+```bash
+# Run with debug-level logging
+./bin/version-guard --verbose
+
+# Production mode (info-level logging only)
+./bin/version-guard
+```
+
+Logs are output in JSON format for easy parsing by log aggregation tools (Datadog, Splunk, CloudWatch Insights):
+
+```json
+{
+  "time": "2024-01-15T10:30:45Z",
+  "level": "WARN",
+  "msg": "failed to detect drift for resource",
+  "resource_id": "arn:aws:rds:us-west-2:123456789012:cluster:my-db",
+  "error": "version not found in EOL database"
+}
+```
+
+Benefits:
+- Machine-readable structured data with typed fields
+- Context-aware logging with trace IDs
+- Queryable logs (e.g., filter by `resource_id` or `error`)
+- Integrates seamlessly with observability platforms
+
 See `./bin/version-guard --help` for all options.
 
 ## 🎨 Classification Policy

cmd/server/main.go

@@ -3,6 +3,7 @@ package main
 import (
 	"context"
 	"fmt"
+	"log/slog"
 	"os"
 	"os/signal"
 	"strings"
@@ -99,6 +100,16 @@ func (s *ServerCLI) buildTagConfig() *wiz.TagConfig {
 }
 
 func (s *ServerCLI) Run(_ *kong.Context) error {
+	// Initialize structured logger
+	logLevel := slog.LevelInfo
+	if s.Verbose {
+		logLevel = slog.LevelDebug
+	}
+	logger := slog.New(slog.NewJSONHandler(os.Stdout, &slog.HandlerOptions{
+		Level: logLevel,
+	}))
+	slog.SetDefault(logger)
+
 	fmt.Println("Starting Version Guard Detector Service (Open Source)")
 	fmt.Printf("  Version: %s\n", version)
 	fmt.Printf("  Temporal Endpoint: %s\n", s.TemporalEndpoint)
@@ -184,17 +195,17 @@ func (s *ServerCLI) Run(_ *kong.Context) error {
 		wizClient := wiz.NewClient(wizHTTPClient, time.Duration(s.WizCacheTTLHours)*time.Hour)
 
 		if s.WizAuroraReportID != "" {
-			invSources[types.ResourceTypeAurora] = wiz.NewAuroraInventorySource(wizClient, s.WizAuroraReportID).
+			invSources[types.ResourceTypeAurora] = wiz.NewAuroraInventorySource(wizClient, s.WizAuroraReportID, logger).
 				WithTagConfig(tagConfig)
 			fmt.Println("✓ Aurora inventory source configured (Wiz)")
 		}
 		if s.WizElastiCacheReportID != "" {
-			invSources[types.ResourceTypeElastiCache] = wiz.NewElastiCacheInventorySource(wizClient, s.WizElastiCacheReportID).
+			invSources[types.ResourceTypeElastiCache] = wiz.NewElastiCacheInventorySource(wizClient, s.WizElastiCacheReportID, logger).
 				WithTagConfig(tagConfig)
 			fmt.Println("✓ ElastiCache inventory source configured (Wiz)")
 		}
 		if s.WizEKSReportID != "" {
-			invSources[types.ResourceTypeEKS] = wiz.NewEKSInventorySource(wizClient, s.WizEKSReportID).
+			invSources[types.ResourceTypeEKS] = wiz.NewEKSInventorySource(wizClient, s.WizEKSReportID, logger).
 				WithTagConfig(tagConfig)
 			fmt.Println("✓ EKS inventory source configured (Wiz)")
 		}
@@ -240,15 +251,15 @@ func (s *ServerCLI) Run(_ *kong.Context) error {
 	cacheTTL := 24 * time.Hour
 
 	// Aurora EOL provider (using endoflife.date for PostgreSQL versions)
-	eolProviders[types.ResourceTypeAurora] = eolendoflife.NewProvider(eolHTTPClient, cacheTTL)
+	eolProviders[types.ResourceTypeAurora] = eolendoflife.NewProvider(eolHTTPClient, cacheTTL, logger)
 	fmt.Println("✓ Aurora EOL provider configured (endoflife.date API)")
 
 	// EKS EOL provider (using endoflife.date for Kubernetes versions)
-	eolProviders[types.ResourceTypeEKS] = eolendoflife.NewProvider(eolHTTPClient, cacheTTL)
+	eolProviders[types.ResourceTypeEKS] = eolendoflife.NewProvider(eolHTTPClient, cacheTTL, logger)
 	fmt.Println("✓ EKS EOL provider configured (endoflife.date API)")
 
 	// ElastiCache EOL provider
-	eolProviders[types.ResourceTypeElastiCache] = eolendoflife.NewProvider(eolHTTPClient, cacheTTL)
+	eolProviders[types.ResourceTypeElastiCache] = eolendoflife.NewProvider(eolHTTPClient, cacheTTL, logger)
 	fmt.Println("✓ ElastiCache EOL provider configured (endoflife.date API)")
 
 	// Initialize policy engine
@@ -261,6 +272,7 @@ func (s *ServerCLI) Run(_ *kong.Context) error {
 			invSources[types.ResourceTypeAurora],
 			eolProviders[types.ResourceTypeAurora],
 			policyEngine,
+			logger,
 		)
 		fmt.Println("✓ Aurora detector initialized")
 	}
@@ -271,6 +283,7 @@ func (s *ServerCLI) Run(_ *kong.Context) error {
 			invSources[types.ResourceTypeEKS],
 			eolProviders[types.ResourceTypeEKS],
 			policyEngine,
+			logger,
 		)
 		fmt.Println("✓ EKS detector initialized")
 	}

pkg/detector/aurora/detector.go

@@ -3,6 +3,7 @@ package aurora
 import (
 	"context"
 	"fmt"
+	"log/slog"
 	"time"
 
 	"github.com/pkg/errors"
@@ -18,18 +19,24 @@ type Detector struct {
 	inventory inventory.InventorySource
 	eol       eol.Provider
 	policy    policy.VersionPolicy
+	logger    *slog.Logger
 }
 
 // NewDetector creates a new Aurora detector
 func NewDetector(
 	inventory inventory.InventorySource,
 	eol eol.Provider,
 	policy policy.VersionPolicy,
+	logger *slog.Logger,
 ) *Detector {
+	if logger == nil {
+		logger = slog.Default()
+	}
 	return &Detector{
 		inventory: inventory,
 		eol:       eol,
 		policy:    policy,
+		logger:    logger,
 	}
 }
 

pkg/detector/aurora/detector_test.go

@@ -49,6 +49,7 @@ func TestDetector_Detect_EOLVersion(t *testing.T) {
 		mockInventory,
 		mockEOL,
 		policy.NewDefaultPolicy(),
+		nil, // logger
 	)
 
 	// Run detection
@@ -119,6 +120,7 @@ func TestDetector_Detect_CurrentVersion(t *testing.T) {
 		mockInventory,
 		mockEOL,
 		policy.NewDefaultPolicy(),
+		nil, // logger
 	)
 
 	// Run detection
@@ -176,6 +178,7 @@ func TestDetector_Detect_ExtendedSupport(t *testing.T) {
 		mockInventory,
 		mockEOL,
 		policy.NewDefaultPolicy(),
+		nil, // logger
 	)
 
 	// Run detection
@@ -257,6 +260,7 @@ func TestDetector_Detect_MultipleResources(t *testing.T) {
 		mockInventory,
 		mockEOL,
 		policy.NewDefaultPolicy(),
+		nil, // logger
 	)
 
 	// Run detection
@@ -311,6 +315,7 @@ func TestDetector_Detect_EmptyInventory(t *testing.T) {
 		mockInventory,
 		mockEOL,
 		policy.NewDefaultPolicy(),
+		nil, // logger
 	)
 
 	// Run detection
@@ -327,7 +332,7 @@ func TestDetector_Detect_EmptyInventory(t *testing.T) {
 }
 
 func TestDetector_Name(t *testing.T) {
-	detector := NewDetector(nil, nil, nil)
+	detector := NewDetector(nil, nil, nil, nil)
 
 	name := detector.Name()
 	expected := "aurora-detector"
@@ -338,7 +343,7 @@ func TestDetector_Name(t *testing.T) {
 }
 
 func TestDetector_ResourceType(t *testing.T) {
-	detector := NewDetector(nil, nil, nil)
+	detector := NewDetector(nil, nil, nil, nil)
 
 	resourceType := detector.ResourceType()
 

pkg/detector/aurora/integration_test.go

@@ -154,6 +154,7 @@ func TestFullFlow_MultipleResourcesWithDifferentStatuses(t *testing.T) {
 		mockInventory,
 		mockEOL,
 		policy.NewDefaultPolicy(),
+		nil, // logger
 	)
 
 	// Execute: Run the full detection flow
@@ -368,7 +369,7 @@ func TestFullFlow_SummaryStatistics(t *testing.T) {
 		},
 	}
 
-	detector := NewDetector(mockInventory, mockEOL, policy.NewDefaultPolicy())
+	detector := NewDetector(mockInventory, mockEOL, policy.NewDefaultPolicy(), nil)
 	findings, err := detector.Detect(context.Background())
 
 	if err != nil {

pkg/detector/eks/detector.go

@@ -2,7 +2,7 @@ package eks
 
 import (
 	"context"
-	"log"
+	"log/slog"
 	"time"
 
 	"github.com/pkg/errors"
@@ -18,18 +18,24 @@ type Detector struct {
 	inventory inventory.InventorySource
 	eol       eol.Provider
 	policy    policy.VersionPolicy
+	logger    *slog.Logger
 }
 
 // NewDetector creates a new EKS detector
 func NewDetector(
 	inventory inventory.InventorySource,
 	eol eol.Provider,
 	policy policy.VersionPolicy,
+	logger *slog.Logger,
 ) *Detector {
+	if logger == nil {
+		logger = slog.Default()
+	}
 	return &Detector{
 		inventory: inventory,
 		eol:       eol,
 		policy:    policy,
+		logger:    logger,
 	}
 }
 
@@ -62,8 +68,9 @@ func (d *Detector) Detect(ctx context.Context) ([]*types.Finding, error) {
 		finding, err := d.detectResource(ctx, resource)
 		if err != nil {
 			// Log error but continue with other resources
-			// TODO: wire through proper structured logger (e.g., *slog.Logger)
-			log.Printf("WARN: failed to detect drift for %s: %v", resource.ID, err)
+			d.logger.WarnContext(ctx, "failed to detect drift for resource",
+				"resource_id", resource.ID,
+				"error", err)
 			continue
 		}
 

pkg/detector/eks/detector_test.go

@@ -49,6 +49,7 @@ func TestDetector_Detect_EOLVersion(t *testing.T) {
 		mockInventory,
 		mockEOL,
 		policy.NewDefaultPolicy(),
+		nil, // logger
 	)
 
 	// Run detection
@@ -119,6 +120,7 @@ func TestDetector_Detect_CurrentVersion(t *testing.T) {
 		mockInventory,
 		mockEOL,
 		policy.NewDefaultPolicy(),
+		nil, // logger
 	)
 
 	// Run detection
@@ -176,6 +178,7 @@ func TestDetector_Detect_ExtendedSupport(t *testing.T) {
 		mockInventory,
 		mockEOL,
 		policy.NewDefaultPolicy(),
+		nil, // logger
 	)
 
 	// Run detection
@@ -257,6 +260,7 @@ func TestDetector_Detect_MultipleResources(t *testing.T) {
 		mockInventory,
 		mockEOL,
 		policy.NewDefaultPolicy(),
+		nil, // logger
 	)
 
 	// Run detection
@@ -311,6 +315,7 @@ func TestDetector_Detect_EmptyInventory(t *testing.T) {
 		mockInventory,
 		mockEOL,
 		policy.NewDefaultPolicy(),
+		nil, // logger
 	)
 
 	// Run detection
@@ -327,7 +332,7 @@ func TestDetector_Detect_EmptyInventory(t *testing.T) {
 }
 
 func TestDetector_Name(t *testing.T) {
-	detector := NewDetector(nil, nil, nil)
+	detector := NewDetector(nil, nil, nil, nil)
 
 	name := detector.Name()
 	expected := "eks-detector"
@@ -338,7 +343,7 @@ func TestDetector_Name(t *testing.T) {
 }
 
 func TestDetector_ResourceType(t *testing.T) {
-	detector := NewDetector(nil, nil, nil)
+	detector := NewDetector(nil, nil, nil, nil)
 
 	resourceType := detector.ResourceType()
 

pkg/detector/eks/integration_test.go

@@ -146,6 +146,7 @@ func TestFullFlow_MultipleResourcesWithDifferentStatuses(t *testing.T) {
 		mockInventory,
 		mockEOL,
 		policy.NewDefaultPolicy(),
+		nil, // logger
 	)
 
 	// Execute: Run detection