Feature/observability

cmd/server/main.go

@@ -31,15 +31,17 @@ func main() {
 	// config + logger
 	cfg := config.Load()
 	logger := ilog.New()
+	defer logger.Sync()
 
 	r := chi.NewRouter()
 
 	r.Use(middleware.RequestID)
+	r.Use(apphttp.MetricsMiddleware)
 	r.Use(middleware.RealIP)
-	r.Use(middleware.Logger)
+	r.Use(apphttp.RequestLogger(logger.Desugar()))
 	r.Use(middleware.Recoverer)
 
-	h := handlers.NewHandler(sqlDB)
+	h := handlers.NewHandler(sqlDB, logger)
 
 	apphttp.Register(r, h)
 

docker-compose.yml

@@ -0,0 +1,18 @@
+services:
+  prometheus:
+    image: prom/prometheus:latest
+    ports:
+      - "9090:9090"
+    volumes:
+      - ./prometheus.yml:/etc/prometheus/prometheus.yml
+    extra_hosts:
+      - "host.docker.internal:host-gateway" # Allows Linux containers to talk to host
+
+  grafana:
+    image: grafana/grafana:latest
+    ports:
+      - "3000:3000"
+    environment:
+      - GF_SECURITY_ADMIN_PASSWORD=admin # Default password
+    depends_on:
+      - prometheus

go.mod

@@ -4,9 +4,27 @@ go 1.25.2
 
 require (
 	github.com/go-chi/chi/v5 v5.2.3
-	github.com/mattn/go-sqlite3 v1.14.32 // indirect
+	github.com/mattn/go-sqlite3 v1.14.32
+	github.com/pressly/goose/v3 v3.26.0
+)
+
+require (
+	github.com/beorn7/perks v1.0.1 // indirect
+	github.com/cespare/xxhash/v2 v2.3.0 // indirect
+	github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 // indirect
+	github.com/prometheus/client_model v0.6.2 // indirect
+	github.com/prometheus/common v0.66.1 // indirect
+	github.com/prometheus/procfs v0.16.1 // indirect
+	go.uber.org/zap v1.27.0 // indirect
+	go.yaml.in/yaml/v2 v2.4.2 // indirect
+	golang.org/x/sys v0.35.0 // indirect
+	google.golang.org/protobuf v1.36.8 // indirect
+)
+
+require (
+	github.com/hashicorp/golang-lru/v2 v2.0.7
 	github.com/mfridman/interpolate v0.0.2 // indirect
-	github.com/pressly/goose/v3 v3.26.0 // indirect
+	github.com/prometheus/client_golang v1.23.2
 	github.com/sethvargo/go-retry v0.3.0 // indirect
 	go.uber.org/multierr v1.11.0 // indirect
 	golang.org/x/sync v0.16.0 // indirect

go.sum

@@ -1,14 +1,69 @@
+github.com/beorn7/perks v1.0.1 h1:VlbKKnNfV8bJzeqoa4cOKqO6bYr3WgKZxO8Z16+hsOM=
+github.com/beorn7/perks v1.0.1/go.mod h1:G2ZrVWU2WbWT9wwq4/hrbKbnv/1ERSJQ0ibhJ6rlkpw=
+github.com/cespare/xxhash/v2 v2.3.0 h1:UL815xU9SqsFlibzuggzjXhog7bL6oX9BbNZnL2UFvs=
+github.com/cespare/xxhash/v2 v2.3.0/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/dustin/go-humanize v1.0.1 h1:GzkhY7T5VNhEkwH0PVJgjz+fX1rhBrR7pRT3mDkpeCY=
+github.com/dustin/go-humanize v1.0.1/go.mod h1:Mu1zIs6XwVuF/gI1OepvI0qD18qycQx+mFykh5fBlto=
 github.com/go-chi/chi/v5 v5.2.3 h1:WQIt9uxdsAbgIYgid+BpYc+liqQZGMHRaUwp0JUcvdE=
 github.com/go-chi/chi/v5 v5.2.3/go.mod h1:L2yAIGWB3H+phAw1NxKwWM+7eUH/lU8pOMm5hHcoops=
+github.com/google/uuid v1.6.0 h1:NIvaJDMOsjHA8n1jAhLSgzrAzy1Hgr+hNrb57e+94F0=
+github.com/google/uuid v1.6.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
+github.com/hashicorp/golang-lru/v2 v2.0.7 h1:a+bsQ5rvGLjzHuww6tVxozPZFVghXaHOwFs4luLUK2k=
+github.com/hashicorp/golang-lru/v2 v2.0.7/go.mod h1:QeFd9opnmA6QUJc5vARoKUSoFhyfM2/ZepoAG6RGpeM=
+github.com/mattn/go-isatty v0.0.20 h1:xfD0iDuEKnDkl03q4limB+vH+GxLEtL/jb4xVJSWWEY=
+github.com/mattn/go-isatty v0.0.20/go.mod h1:W+V8PltTTMOvKvAeJH7IuucS94S2C6jfK/D7dTCTo3Y=
 github.com/mattn/go-sqlite3 v1.14.32 h1:JD12Ag3oLy1zQA+BNn74xRgaBbdhbNIDYvQUEuuErjs=
 github.com/mattn/go-sqlite3 v1.14.32/go.mod h1:Uh1q+B4BYcTPb+yiD3kU8Ct7aC0hY9fxUwlHK0RXw+Y=
 github.com/mfridman/interpolate v0.0.2 h1:pnuTK7MQIxxFz1Gr+rjSIx9u7qVjf5VOoM/u6BbAxPY=
 github.com/mfridman/interpolate v0.0.2/go.mod h1:p+7uk6oE07mpE/Ik1b8EckO0O4ZXiGAfshKBWLUM9Xg=
+github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 h1:C3w9PqII01/Oq1c1nUAm88MOHcQC9l5mIlSMApZMrHA=
+github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822/go.mod h1:+n7T8mK8HuQTcFwEeznm/DIxMOiR9yIdICNftLE1DvQ=
+github.com/ncruces/go-strftime v0.1.9 h1:bY0MQC28UADQmHmaF5dgpLmImcShSi2kHU9XLdhx/f4=
+github.com/ncruces/go-strftime v0.1.9/go.mod h1:Fwc5htZGVVkseilnfgOVb9mKy6w1naJmn9CehxcKcls=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/pressly/goose/v3 v3.26.0 h1:KJakav68jdH0WDvoAcj8+n61WqOIaPGgH0bJWS6jpmM=
 github.com/pressly/goose/v3 v3.26.0/go.mod h1:4hC1KrritdCxtuFsqgs1R4AU5bWtTAf+cnWvfhf2DNY=
+github.com/prometheus/client_golang v1.23.2 h1:Je96obch5RDVy3FDMndoUsjAhG5Edi49h0RJWRi/o0o=
+github.com/prometheus/client_golang v1.23.2/go.mod h1:Tb1a6LWHB3/SPIzCoaDXI4I8UHKeFTEQ1YCr+0Gyqmg=
+github.com/prometheus/client_model v0.6.2 h1:oBsgwpGs7iVziMvrGhE53c/GrLUsZdHnqNwqPLxwZyk=
+github.com/prometheus/client_model v0.6.2/go.mod h1:y3m2F6Gdpfy6Ut/GBsUqTWZqCUvMVzSfMLjcu6wAwpE=
+github.com/prometheus/common v0.66.1 h1:h5E0h5/Y8niHc5DlaLlWLArTQI7tMrsfQjHV+d9ZoGs=
+github.com/prometheus/common v0.66.1/go.mod h1:gcaUsgf3KfRSwHY4dIMXLPV0K/Wg1oZ8+SbZk/HH/dA=
+github.com/prometheus/procfs v0.16.1 h1:hZ15bTNuirocR6u0JZ6BAHHmwS1p8B4P6MRqxtzMyRg=
+github.com/prometheus/procfs v0.16.1/go.mod h1:teAbpZRB1iIAJYREa1LsoWUXykVXA1KlTmWl8x/U+Is=
+github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec h1:W09IVJc94icq4NjY3clb7Lk8O1qJ8BdBEF8z0ibU0rE=
+github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec/go.mod h1:qqbHyh8v60DhA7CoWK5oRCqLrMHRGoxYCSS9EjAz6Eo=
 github.com/sethvargo/go-retry v0.3.0 h1:EEt31A35QhrcRZtrYFDTBg91cqZVnFL2navjDrah2SE=
 github.com/sethvargo/go-retry v0.3.0/go.mod h1:mNX17F0C/HguQMyMyJxcnU471gOZGxCLyYaFyAZraas=
+github.com/stretchr/testify v1.11.0 h1:ib4sjIrwZKxE5u/Japgo/7SJV3PvgjGiRNAvTVGqQl8=
+github.com/stretchr/testify v1.11.0/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
 go.uber.org/multierr v1.11.0 h1:blXXJkSxSSfBVBlC76pxqeO+LN3aDfLQo+309xJstO0=
 go.uber.org/multierr v1.11.0/go.mod h1:20+QtiLqy0Nd6FdQB9TLXag12DsQkrbs3htMFfDN80Y=
+go.uber.org/zap v1.27.0 h1:aJMhYGrd5QSmlpLMr2MftRKl7t8J8PTZPA732ud/XR8=
+go.uber.org/zap v1.27.0/go.mod h1:GB2qFLM7cTU87MWRP2mPIjqfIDnGu+VIO4V/SdhGo2E=
+go.yaml.in/yaml/v2 v2.4.2 h1:DzmwEr2rDGHl7lsFgAHxmNz/1NlQ7xLIrlN2h5d1eGI=
+go.yaml.in/yaml/v2 v2.4.2/go.mod h1:081UH+NErpNdqlCXm3TtEran0rJZGxAYx9hb/ELlsPU=
+golang.org/x/exp v0.0.0-20250620022241-b7579e27df2b h1:M2rDM6z3Fhozi9O7NWsxAkg/yqS/lQJ6PmkyIV3YP+o=
+golang.org/x/exp v0.0.0-20250620022241-b7579e27df2b/go.mod h1:3//PLf8L/X+8b4vuAfHzxeRUl04Adcb341+IGKfnqS8=
 golang.org/x/sync v0.16.0 h1:ycBJEhp9p4vXvUZNszeOq0kGTPghopOL8q0fq3vstxw=
 golang.org/x/sync v0.16.0/go.mod h1:1dzgHSNfp02xaA81J2MS99Qcpr2w7fw1gpm99rleRqA=
+golang.org/x/sys v0.34.0 h1:H5Y5sJ2L2JRdyv7ROF1he/lPdvFsd0mJHFw2ThKHxLA=
+golang.org/x/sys v0.34.0/go.mod h1:BJP2sWEmIv4KK5OTEluFJCKSidICx8ciO85XgH3Ak8k=
+golang.org/x/sys v0.35.0 h1:vz1N37gP5bs89s7He8XuIYXpyY0+QlsKmzipCbUtyxI=
+golang.org/x/sys v0.35.0/go.mod h1:BJP2sWEmIv4KK5OTEluFJCKSidICx8ciO85XgH3Ak8k=
+google.golang.org/protobuf v1.36.8 h1:xHScyCOEuuwZEc6UtSOvPbAT4zRh0xcNRYekJwfqyMc=
+google.golang.org/protobuf v1.36.8/go.mod h1:fuxRtAxBytpl4zzqUh6/eyUujkJdNiuEkXntxiD/uRU=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
+modernc.org/libc v1.66.3 h1:cfCbjTUcdsKyyZZfEUKfoHcP3S0Wkvz3jgSzByEWVCQ=
+modernc.org/libc v1.66.3/go.mod h1:XD9zO8kt59cANKvHPXpx7yS2ELPheAey0vjIuZOhOU8=
+modernc.org/mathutil v1.7.1 h1:GCZVGXdaN8gTqB1Mf/usp1Y/hSqgI2vAGGP4jZMCxOU=
+modernc.org/mathutil v1.7.1/go.mod h1:4p5IwJITfppl0G4sUEDtCr4DthTaT47/N3aT6MhfgJg=
+modernc.org/memory v1.11.0 h1:o4QC8aMQzmcwCK3t3Ux/ZHmwFPzE6hf2Y5LbkRs+hbI=
+modernc.org/memory v1.11.0/go.mod h1:/JP4VbVC+K5sU2wZi9bHoq2MAkCnrt2r98UGeSK7Mjw=
+modernc.org/sqlite v1.38.2 h1:Aclu7+tgjgcQVShZqim41Bbw9Cho0y/7WzYptXqkEek=
+modernc.org/sqlite v1.38.2/go.mod h1:cPTJYSlgg3Sfg046yBShXENNtPrWrDX8bsbAQBzgQ5E=

internal/http/handlers/handlers.go

@@ -2,12 +2,22 @@ package handlers
 
 import (
 	"database/sql"
+
+	lru "github.com/hashicorp/golang-lru/v2"
+	ilog "github.com/joeynolan/go-http-server/internal/platform/log"
 )
 
 type Handler struct {
-	DB *sql.DB
+	DB    *sql.DB
+	Log   *ilog.Logger
+	cache *lru.Cache[string, string]
 }
 
-func NewHandler(db *sql.DB) *Handler {
-	return &Handler{DB: db}
+func NewHandler(db *sql.DB, logger *ilog.Logger) *Handler {
+	cache, _ := lru.New[string, string](32)
+	return &Handler{
+		DB:    db,
+		Log:   logger,
+		cache: cache,
+	}
 }

internal/http/handlers/redirect.go

@@ -6,30 +6,33 @@ import (
 	"strings"
 
 	"github.com/go-chi/chi/v5"
-	ilog "github.com/joeynolan/go-http-server/internal/platform/log"
 )
 
 func (h *Handler) RedirectHandler(w http.ResponseWriter, r *http.Request) {
-	logger := ilog.New()
-
 	code := chi.URLParam(r, "code")
 	if code == "" {
 		WriteError(w, http.StatusBadRequest, "missing code")
 		return
 	}
 
 	var url string
-	logger.Infof("Code: %s", code)
-	err := h.DB.QueryRowContext(r.Context(), "SELECT url FROM links WHERE code = ?", code).Scan(&url)
-	logger.Infof("URL: %s", url)
-	if err == sql.ErrNoRows {
-		WriteError(w, http.StatusNotFound, "code not found")
-		return
-	}
-	if err != nil {
-		WriteError(w, http.StatusInternalServerError, "lookup failed")
-		return
+	h.Log.Infof("Code: %s", code)
+	if val, ok := h.cache.Get(code); ok {
+		h.Log.Infof("Cache hit for code: %s", code)
+		url = val
+	} else {
+		err := h.DB.QueryRowContext(r.Context(), "SELECT url FROM links WHERE code = ?", code).Scan(&url)
+		if err == sql.ErrNoRows {
+			WriteError(w, http.StatusNotFound, "code not found")
+			return
+		}
+		if err != nil {
+			WriteError(w, http.StatusInternalServerError, "lookup failed")
+			return
+		}
+		h.cache.Add(code, url)
 	}
+	h.Log.Infof("URL: %s", url)
 
 	target := url
 	if !strings.HasPrefix(target, "http://") && !strings.HasPrefix(target, "https://") {

internal/http/logging.go

@@ -0,0 +1,33 @@
+package http
+
+import (
+	"net/http"
+	"time"
+
+	"github.com/go-chi/chi/v5/middleware"
+	"go.uber.org/zap"
+)
+
+// RequestLogger logs request/response metadata with zap.
+func RequestLogger(logger *zap.Logger) func(http.Handler) http.Handler {
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			start := time.Now()
+			ww := middleware.NewWrapResponseWriter(w, r.ProtoMajor)
+			reqID := middleware.GetReqID(r.Context())
+
+			next.ServeHTTP(ww, r)
+
+			logger.Info("request completed",
+				zap.String("req_id", reqID),
+				zap.String("method", r.Method),
+				zap.String("path", r.URL.Path),
+				zap.Int("status", ww.Status()),
+				zap.Int("bytes", ww.BytesWritten()),
+				zap.Duration("latency", time.Since(start)),
+				zap.String("remote", r.RemoteAddr),
+				zap.String("user_agent", r.UserAgent()),
+			)
+		})
+	}
+}

internal/http/metrics.go

@@ -0,0 +1,67 @@
+package http
+
+import (
+	"net/http"
+	"strconv"
+	"time"
+
+	"github.com/go-chi/chi/v5"
+	"github.com/go-chi/chi/v5/middleware"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+)
+
+var (
+	httpRequestsTotal = promauto.NewCounterVec(
+		prometheus.CounterOpts{
+			Name: "http_requests_total",
+			Help: "Total HTTP requests processed.",
+		},
+		[]string{"method", "route", "status"},
+	)
+
+	httpRequestDuration = promauto.NewHistogramVec(
+		prometheus.HistogramOpts{
+			Name:    "http_request_duration_seconds",
+			Help:    "HTTP request duration in seconds.",
+			Buckets: prometheus.DefBuckets,
+		},
+		[]string{"method", "route", "status"},
+	)
+)
+
+// MetricsMiddleware records request count and latency by method/route/status.
+func MetricsMiddleware(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		start := time.Now()
+		ww := middleware.NewWrapResponseWriter(w, r.ProtoMajor)
+
+		next.ServeHTTP(ww, r)
+
+		route := routePattern(r)
+		statusCode := ww.Status()
+		labels := prometheus.Labels{
+			"method": r.Method,
+			"route":  route,
+			"status": strconv.Itoa(statusCode),
+		}
+
+		httpRequestsTotal.With(labels).Inc()
+		httpRequestDuration.With(labels).Observe(time.Since(start).Seconds())
+	})
+}
+
+// MetricsHandler exposes the Prometheus scrape endpoint.
+func MetricsHandler() http.Handler {
+	return promhttp.Handler()
+}
+
+func routePattern(r *http.Request) string {
+	if rctx := chi.RouteContext(r.Context()); rctx != nil {
+		if rp := rctx.RoutePattern(); rp != "" {
+			return rp
+		}
+	}
+	return "unknown"
+}

internal/http/router.go

@@ -9,4 +9,5 @@ func Register(r chi.Router, h *handlers.Handler) {
 	r.Get("/health", handlers.HealthHandler)
 	r.Get("/v1/r/{code}", h.RedirectHandler)
 	r.Post("/v1/shorten", h.ShortenHandler)
+	r.Handle("/metrics", MetricsHandler())
 }

internal/platform/log/log.go

@@ -1,20 +1,41 @@
 package log
 
 import (
-	"fmt"
-	"log"
+	"go.uber.org/zap"
+	"go.uber.org/zap/zapcore"
 )
 
-type Logger struct{}
+// Logger wraps a zap logger so callers can keep using familiar sugar helpers.
+type Logger struct {
+	*zap.SugaredLogger
+	base *zap.Logger
+}
 
-func New() *Logger { return &Logger{} }
+// New returns a production-ready zap logger.
+func New() *Logger {
+	cfg := zap.NewProductionConfig()
+	cfg.EncoderConfig.TimeKey = "ts"
+	cfg.EncoderConfig.MessageKey = "msg"
+	cfg.EncoderConfig.LevelKey = "level"
+	cfg.EncoderConfig.EncodeTime = zapcore.ISO8601TimeEncoder
 
-func (l *Logger) Infof(format string, v ...any)  { log.Printf("INFO  "+format, v...) }
-func (l *Logger) Errorf(format string, v ...any) { log.Printf("ERROR "+format, v...) }
+	base, err := cfg.Build()
+	if err != nil {
+		panic(err)
+	}
 
-// Optional convenience
-func (l *Logger) Println(v ...any)          { log.Println(v...) }
-func (l *Logger) Printf(f string, v ...any) { log.Printf(f, v...) }
+	return &Logger{
+		SugaredLogger: base.Sugar(),
+		base:          base,
+	}
+}
 
-// Example usage: logger.Infof("starting on :%d", port)
-func Sprintf(f string, v ...any) string { return fmt.Sprintf(f, v...) }
+// Sync flushes any buffered log entries.
+func (l *Logger) Sync() {
+	_ = l.base.Sync()
+}
+
+// Desugar exposes the underlying structured logger.
+func (l *Logger) Desugar() *zap.Logger {
+	return l.base
+}

prometheus.yml

@@ -0,0 +1,7 @@
+global:
+  scrape_interval: 5s # Scrape often for dev/learning (default is usually 1m)
+
+scrape_configs:
+  - job_name: 'go_app'
+    static_configs:
+      - targets: ['host.docker.internal:8080'] # <--- CRITICAL: Points to your host machine