feat!: add prometheus metrics support

- Add arguments `-prometheus-metrics-enabled` and
  `-prometheus-listen-addr` to control whether to expose metrics from
  the registry app.
- The `ModuleStore` interface has received an extra method `Metrics()`
  to support store-specific metrics.

Author: stigok

cmd/terraform-registry/main.go

@@ -25,23 +25,27 @@ import (
 	"github.com/nrkno/terraform-registry/pkg/registry"
 	"github.com/nrkno/terraform-registry/pkg/store/github"
 	"github.com/nrkno/terraform-registry/pkg/store/s3"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
 	"go.uber.org/zap"
 )
 
 var (
-	listenAddr            string
-	accessLogDisabled     bool
-	accessLogIgnoredPaths string
-	authDisabled          bool
-	authTokensFile        string
-	envJSONFiles          string
-	tlsEnabled            bool
-	tlsCertFile           string
-	tlsKeyFile            string
-	storeType             string
-	logLevelStr           string
-	logFormatStr          string
-	printVersionInfo      bool
+	listenAddr               string
+	accessLogDisabled        bool
+	accessLogIgnoredPaths    string
+	authDisabled             bool
+	authTokensFile           string
+	envJSONFiles             string
+	tlsEnabled               bool
+	tlsCertFile              string
+	tlsKeyFile               string
+	storeType                string
+	prometheusListenAddr     string
+	prometheusMetricsEnabled bool
+	logLevelStr              string
+	logFormatStr             string
+	printVersionInfo         bool
 
 	S3Region string
 	S3Bucket string
@@ -84,6 +88,8 @@ func init() {
 	flag.StringVar(&logLevelStr, "log-level", "info", "Levels: debug, info, warn, error")
 	flag.StringVar(&logFormatStr, "log-format", "console", "Formats: json, console")
 	flag.BoolVar(&printVersionInfo, "version", false, "Print version info and exit")
+	flag.StringVar(&prometheusListenAddr, "prometheus-listen-addr", ":9090", "Listen address where /metrics endpoint is exposed.")
+	flag.BoolVar(&prometheusMetricsEnabled, "prometheus-metrics-enabled", false, "Enable the Prometheus metrics endpoint.")
 
 	flag.StringVar(&gitHubOwnerFilter, "github-owner-filter", "", "GitHub org/user repository filter")
 	flag.StringVar(&gitHubTopicFilter, "github-topic-filter", "", "GitHub topic repository filter")
@@ -187,6 +193,13 @@ func main() {
 		logger.Fatal("invalid store type", zap.String("selected", storeType))
 	}
 
+	if prometheusMetricsEnabled {
+		mux := http.NewServeMux()
+		mux.Handle("/metrics", promhttp.Handler())
+		prometheus.MustRegister(reg.Metrics())
+		go prometheusListenAndServe(mux)
+	}
+
 	listenAndServe(reg)
 }
 
@@ -217,6 +230,33 @@ func listenAndServe(handler http.Handler) {
 	}
 }
 
+func prometheusListenAndServe(handler http.Handler) {
+	srv := http.Server{
+		Addr:              prometheusListenAddr,
+		Handler:           handler,
+		ReadTimeout:       3 * time.Second,
+		ReadHeaderTimeout: 3 * time.Second,
+		WriteTimeout:      3 * time.Second,
+		IdleTimeout:       60 * time.Second, // keep-alive timeout
+	}
+
+	logger.Info("starting Prometheus metrics HTTP server",
+		zap.Bool("tls", tlsEnabled),
+		zap.String("listenAddr", prometheusListenAddr),
+	)
+	if tlsEnabled {
+		err := srv.ListenAndServeTLS(tlsCertFile, tlsKeyFile)
+		logger.Panic("prometheusListenAndServe",
+			zap.Errors("err", []error{err}),
+		)
+	} else {
+		err := srv.ListenAndServe()
+		logger.Panic("prometheusListenAndServe",
+			zap.Errors("err", []error{err}),
+		)
+	}
+}
+
 // watchFile reads the contents of the file at `filename`, first immediately, then at at every `interval`.
 // If and only if the file contents have changed since the last invocation of `callback` it is called again.
 // Note that the callback will always be called initially when this function is called.

go.mod

@@ -16,23 +16,31 @@ require (
 	github.com/hashicorp/go-version v1.6.0
 	github.com/matryer/is v1.4.1
 	github.com/migueleliasweb/go-github-mock v0.0.23
+	github.com/prometheus/client_golang v1.18.0
 	github.com/stretchr/testify v1.8.4
 	go.uber.org/zap v1.27.0
 	golang.org/x/oauth2 v0.17.0
 )
 
 require (
+	github.com/beorn7/perks v1.0.1 // indirect
+	github.com/cespare/xxhash/v2 v2.2.0 // indirect
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/golang/protobuf v1.5.3 // indirect
 	github.com/google/go-github/v59 v59.0.0 // indirect
 	github.com/google/go-querystring v1.1.0 // indirect
 	github.com/gorilla/mux v1.8.0 // indirect
 	github.com/jmespath/go-jmespath v0.4.0 // indirect
+	github.com/matttproud/golang_protobuf_extensions/v2 v2.0.0 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/prometheus/client_model v0.5.0 // indirect
+	github.com/prometheus/common v0.45.0 // indirect
+	github.com/prometheus/procfs v0.12.0 // indirect
 	github.com/stretchr/objx v0.5.0 // indirect
 	go.uber.org/multierr v1.10.0 // indirect
 	golang.org/x/crypto v0.19.0 // indirect
 	golang.org/x/net v0.21.0 // indirect
+	golang.org/x/sys v0.17.0 // indirect
 	golang.org/x/time v0.3.0 // indirect
 	google.golang.org/appengine v1.6.7 // indirect
 	google.golang.org/protobuf v1.31.0 // indirect

go.sum

@@ -1,5 +1,9 @@
 github.com/aws/aws-sdk-go v1.50.25 h1:vhiHtLYybv1Nhx3Kv18BBC6L0aPJHaG9aeEsr92W99c=
 github.com/aws/aws-sdk-go v1.50.25/go.mod h1:LF8svs817+Nz+DmiMQKTO3ubZ/6IaTpq3TjupRn3Eqk=
+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 v2.2.0 h1:DC2CZ1Ep5Y4k3ZQ899DldepgrayRUGE6BBZ/cd9Cj44=
+github.com/cespare/xxhash/v2 v2.2.0/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 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=
@@ -27,12 +31,28 @@ github.com/jmespath/go-jmespath v0.4.0 h1:BEgLn5cpjn8UN1mAw4NjwDrS35OdebyEtFe+9Y
 github.com/jmespath/go-jmespath v0.4.0/go.mod h1:T8mJZnbsbmF+m6zOOFylbeCJqk5+pHWvzYPziyZiYoo=
 github.com/jmespath/go-jmespath/internal/testify v1.5.1 h1:shLQSRRSCCPj3f2gpwzGwWFoC7ycTf1rcQZHOlsJ6N8=
 github.com/jmespath/go-jmespath/internal/testify v1.5.1/go.mod h1:L3OGu8Wl2/fWfCI6z80xFu9LTZmf1ZRjMHUOPmWr69U=
+github.com/kr/pretty v0.3.1 h1:flRD4NNwYAUpkphVc1HcthR4KEIFJ65n8Mw5qdRn3LE=
+github.com/kr/pretty v0.3.1/go.mod h1:hoEshYVHaxMs3cyo3Yncou5ZscifuDolrwPKZanG3xk=
+github.com/kr/text v0.2.0 h1:5Nx0Ya0ZqY2ygV366QzturHI13Jq95ApcVaJBhpS+AY=
+github.com/kr/text v0.2.0/go.mod h1:eLer722TekiGuMkidMxC/pM04lWEeraHUUmBw8l2grE=
 github.com/matryer/is v1.4.1 h1:55ehd8zaGABKLXQUe2awZ99BD/PTc2ls+KV/dXphgEQ=
 github.com/matryer/is v1.4.1/go.mod h1:8I/i5uYgLzgsgEloJE1U6xx5HkBQpAZvepWuujKwMRU=
+github.com/matttproud/golang_protobuf_extensions/v2 v2.0.0 h1:jWpvCLoY8Z/e3VKvlsiIGKtc+UG6U5vzxaoagmhXfyg=
+github.com/matttproud/golang_protobuf_extensions/v2 v2.0.0/go.mod h1:QUyp042oQthUoa9bqDv0ER0wrtXnBruoNd7aNjkbP+k=
 github.com/migueleliasweb/go-github-mock v0.0.23 h1:GOi9oX/+Seu9JQ19V8bPDLqDI7M9iEOjo3g8v1k6L2c=
 github.com/migueleliasweb/go-github-mock v0.0.23/go.mod h1:NsT8FGbkvIZQtDu38+295sZEX8snaUiiQgsGxi6GUxk=
 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/prometheus/client_golang v1.18.0 h1:HzFfmkOzH5Q8L8G+kSJKUx5dtG87sewO+FoDDqP5Tbk=
+github.com/prometheus/client_golang v1.18.0/go.mod h1:T+GXkCk5wSJyOqMIzVgvvjFDlkOQntgjkJWKrN5txjA=
+github.com/prometheus/client_model v0.5.0 h1:VQw1hfvPvk3Uv6Qf29VrPF32JB6rtbgI6cYPYQjL0Qw=
+github.com/prometheus/client_model v0.5.0/go.mod h1:dTiFglRmd66nLR9Pv9f0mZi7B7fk5Pm3gvsjB5tr+kI=
+github.com/prometheus/common v0.45.0 h1:2BGz0eBc2hdMDLnO/8n0jeB3oPrt2D08CekT0lneoxM=
+github.com/prometheus/common v0.45.0/go.mod h1:YJmSTw9BoKxJplESWWxlbyttQR4uaEcGyv9MZjVOJsY=
+github.com/prometheus/procfs v0.12.0 h1:jluTpSng7V9hY0O2R9DzzJHYb2xULk9VTR1V1R/k6Bo=
+github.com/prometheus/procfs v0.12.0/go.mod h1:pcuDEFsWDnvcgNzo4EEweacyhjeA9Zk3cnaOZAZEfOo=
+github.com/rogpeppe/go-internal v1.10.0 h1:TMyTOH3F/DB16zRVcYyreMH6GnZZrwQVAoYjRBZyWFQ=
+github.com/rogpeppe/go-internal v1.10.0/go.mod h1:UQnix2H7Ngw/k4C5ijL5+65zddjncjaFoBhdsK/akog=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/objx v0.4.0/go.mod h1:YvHI0jy2hoMjB+UWwv71VJQ9isScKT/TqJzVSSt89Yw=
 github.com/stretchr/objx v0.5.0 h1:1zr/of2m5FGMsad5YfcqgdqdWrIhu+EBEJRhR1U7z/c=
@@ -56,6 +76,8 @@ golang.org/x/net v0.21.0/go.mod h1:bIjVDfnllIU7BJ2DNgfnXvpSvtn8VRwhlsaeUTyUS44=
 golang.org/x/oauth2 v0.17.0 h1:6m3ZPmLEFdVxKKWnKq4VqZ60gutO35zm+zrAHVmHyDQ=
 golang.org/x/oauth2 v0.17.0/go.mod h1:OzPDGQiuQMguemayvdylqddI7qcD9lnSDb+1FiwQ5HA=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/sys v0.17.0 h1:25cE3gD+tdBA7lp7QfhuV+rJiE9YXTcS3VG1SqssI/Y=
+golang.org/x/sys v0.17.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/text v0.3.2/go.mod h1:bEr9sfX3Q8Zfm5fL9x+3itogRgK3+ptLWKqgva+5dAk=
 golang.org/x/text v0.14.0 h1:ScX5w1eTa3QqT8oi6+ziP7dTV1S2+ALU0bI+0zXKWiQ=
@@ -70,10 +92,12 @@ google.golang.org/protobuf v1.26.0-rc.1/go.mod h1:jlhhOSvTdKEhbULTjvd4ARK9grFBp0
 google.golang.org/protobuf v1.26.0/go.mod h1:9q0QmTI4eRPtz6boOQmLYwt+qCgq0jsYwAQnmE0givc=
 google.golang.org/protobuf v1.31.0 h1:g0LDEJHgrBl9N9r17Ru3sqWhkIx2NB67okBHPwC7hs8=
 google.golang.org/protobuf v1.31.0/go.mod h1:HV8QOd/L58Z+nl8r43ehVNZIU/HEI6OcFqwMG9pJV4I=
-gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
-gopkg.in/yaml.v2 v2.2.8 h1:obN1ZagJSUGI0Ek/LBmuj4SNLPfIny3KsKFopxRdj10=
+gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c h1:Hei/4ADfdWqJk1ZMxUNpqntNwaWcugrBjAiHlqqRiVk=
+gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c/go.mod h1:JHkPIbrfpd72SG/EVd6muEfDQjcINNoR0C8j2r3qZ4Q=
 gopkg.in/yaml.v2 v2.2.8/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
+gopkg.in/yaml.v2 v2.4.0 h1:D8xgwECY7CYvx+Y2n4sBz93Jn9JRvxdiyyo8CTfuKaY=
+gopkg.in/yaml.v2 v2.4.0/go.mod h1:RDklbk79AGWmwhnvt/jBztapEOGDOx6ZbXqjP6csGnQ=
 gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
 gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

pkg/core/core.go

@@ -5,7 +5,11 @@
 
 package core
 
-import "context"
+import (
+	"context"
+
+	"github.com/prometheus/client_golang/prometheus"
+)
 
 type ModuleVersion struct {
 	// Version is a SemVer version string that specifies the version for a module.
@@ -19,4 +23,5 @@ type ModuleVersion struct {
 type ModuleStore interface {
 	ListModuleVersions(ctx context.Context, namespace, name, provider string) ([]*ModuleVersion, error)
 	GetModuleVersion(ctx context.Context, namespace, name, provider, version string) (*ModuleVersion, error)
+	Metrics() []prometheus.Collector
 }

pkg/registry/registry.go

@@ -16,6 +16,7 @@ import (
 	"github.com/go-chi/chi/v5"
 	"github.com/go-chi/chi/v5/middleware"
 	"github.com/nrkno/terraform-registry/pkg/core"
+	"github.com/prometheus/client_golang/prometheus"
 	"go.uber.org/zap"
 )
 
@@ -152,6 +153,20 @@ func (reg *Registry) RequestLogger() func(next http.Handler) http.Handler {
 
 // SPDX-SnippetEnd
 
+// Metrics returns a Prometheus registry containing metrics for the module store.
+func (reg *Registry) Metrics() *prometheus.Registry {
+	root := prometheus.NewRegistry()
+
+	if reg.moduleStore != nil {
+		modules := prometheus.NewRegistry()
+		modules.MustRegister(reg.moduleStore.Metrics()...)
+		prometheus.WrapRegistererWithPrefix("store_module_", modules)
+		root.MustRegister(modules)
+	}
+
+	return root
+}
+
 func (reg *Registry) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	reg.router.ServeHTTP(w, r)
 }

pkg/store/github/github.go

@@ -14,6 +14,7 @@ import (
 	"github.com/google/go-github/v43/github"
 	goversion "github.com/hashicorp/go-version"
 	"github.com/nrkno/terraform-registry/pkg/core"
+	"github.com/prometheus/client_golang/prometheus"
 	"go.uber.org/zap"
 	"golang.org/x/oauth2"
 )
@@ -200,3 +201,7 @@ func (s *GitHubStore) searchRepositories(ctx context.Context) ([]*github.Reposit
 
 	return allRepos, nil
 }
+
+func (s *GitHubStore) Metrics() []prometheus.Collector {
+	return nil
+}

pkg/store/memory/memory.go

@@ -11,6 +11,7 @@ import (
 	"sync"
 
 	"github.com/nrkno/terraform-registry/pkg/core"
+	"github.com/prometheus/client_golang/prometheus"
 )
 
 // MemoryStore is an in-memory store implementation without a backend.
@@ -72,3 +73,7 @@ func (s *MemoryStore) GetModuleVersion(ctx context.Context, namespace, name, pro
 
 	return nil, fmt.Errorf("version '%s' not found for module '%s'", version, key)
 }
+
+func (s *MemoryStore) Metrics() []prometheus.Collector {
+	return nil
+}

pkg/store/s3/s3.go

@@ -13,6 +13,7 @@ import (
 	"github.com/aws/aws-sdk-go/service/s3"
 	"github.com/aws/aws-sdk-go/service/s3/s3iface"
 	"github.com/nrkno/terraform-registry/pkg/core"
+	"github.com/prometheus/client_golang/prometheus"
 	"go.uber.org/zap"
 )
 
@@ -144,3 +145,7 @@ func isValidModuleSourcePath(path string) bool {
 	r := regexp.MustCompile("^" + addrRegExp + "/" + verRegExp)
 	return r.MatchString(path)
 }
+
+func (s *S3Store) Metrics() []prometheus.Collector {
+	return nil
+}