From 9d580c30cf752eac8fa12b0332addb5f3c2f504a Mon Sep 17 00:00:00 2001
From: Dan Fuhry <dan@fuhry.com>
Date: Fri, 21 Mar 2025 23:07:41 -0400
Subject: [PATCH] add prometheus_http_discovery program

---
 .gitignore                                    |   1 +
 metrics/prometheus_http_discovery/Makefile    |  14 +++
 metrics/prometheus_http_discovery/main.go     | 115 ++++++++++++++++++
 .../systemd/prometheus-http-discovery.service |  10 ++
 4 files changed, 140 insertions(+)
 create mode 100644 metrics/prometheus_http_discovery/Makefile
 create mode 100644 metrics/prometheus_http_discovery/main.go
 create mode 100644 metrics/prometheus_http_discovery/systemd/prometheus-http-discovery.service

diff --git a/.gitignore b/.gitignore
index de7cd73..50a6a0b 100644
--- a/.gitignore
+++ b/.gitignore
@@ -53,6 +53,7 @@ http/samlproxy/samlproxy
 automation/bryston_ctl/cli/cli
 automation/bryston_ctl/client/client
 automation/bryston_ctl/server/server
+metrics/prometheus_http_discovery/prometheus_http_discovery
 
 /vendor/
 
diff --git a/metrics/prometheus_http_discovery/Makefile b/metrics/prometheus_http_discovery/Makefile
new file mode 100644
index 0000000..bfab546
--- /dev/null
+++ b/metrics/prometheus_http_discovery/Makefile
@@ -0,0 +1,14 @@
+GOSRC = $(wildcard *.go)
+GOEXE = $(shell basename `pwd`)
+GOBUILDFLAGS := -buildmode=pie -trimpath
+
+all: $(GOEXE)
+
+clean:
+	rm -fv $(GOEXE)
+
+.PHONY: all clean
+
+$(GOEXE): %: $(GOSRC)
+	go build $(GOBUILDFLAGS) -o $@ $<
+
diff --git a/metrics/prometheus_http_discovery/main.go b/metrics/prometheus_http_discovery/main.go
new file mode 100644
index 0000000..7e6462a
--- /dev/null
+++ b/metrics/prometheus_http_discovery/main.go
@@ -0,0 +1,115 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"flag"
+	"fmt"
+	"net/http"
+	"os/signal"
+	"sync"
+	"syscall"
+	"time"
+
+	"github.com/coreos/go-systemd/daemon"
+
+	"go.fuhry.dev/runtime/constants"
+	"go.fuhry.dev/runtime/mtls"
+	"go.fuhry.dev/runtime/sd"
+	"go.fuhry.dev/runtime/utils/log"
+)
+
+type endpoint struct {
+	Targets []string          `json:"targets"`
+	Labels  map[string]string `json:"labels"`
+}
+
+func main() {
+	mtls.SetDefaultIdentity("node-exporter")
+	ctx, _ := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
+	serverCtx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	port := flag.Uint("port", 9102, "port to listen on")
+
+	flag.Parse()
+
+	id := mtls.DefaultIdentity()
+	tlsConfig, err := id.TlsConfig(serverCtx)
+	if err != nil {
+		log.Panic(err)
+	}
+	pv := mtls.NewPeerNameVerifier()
+	pv.AllowFrom(mtls.Service, "prometheus")
+	pv.AllowFrom(mtls.Service, "healthcheck")
+	err = pv.ConfigureServer(tlsConfig)
+	if err != nil {
+		log.Panic(err)
+	}
+
+	mux := http.NewServeMux()
+	loggingMiddleware := log.NewLoggingMiddleware(mux)
+	sdWatchers := make(map[string]*sd.SDWatcher, 0)
+	sdLock := sync.Mutex{}
+	mux.HandleFunc("/healthz", func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+		w.Write([]byte(fmt.Sprintf("<h1>%s Prometheus HTTP discovery servicer</h1>", constants.OrgName)))
+	})
+	mux.HandleFunc("/endpoints/{service}", func(w http.ResponseWriter, r *http.Request) {
+		service := r.PathValue("service")
+		sdLock.Lock()
+		if _, ok := sdWatchers[service]; !ok {
+			sdWatchers[service] = &sd.SDWatcher{
+				Service:  service,
+				Protocol: sd.ProtocolTCP,
+			}
+		}
+		watcher := sdWatchers[service]
+		sdLock.Unlock()
+
+		endpoints, err := watcher.GetAddrs(serverCtx)
+		if err != nil {
+			w.WriteHeader(http.StatusInternalServerError)
+			w.Write([]byte(err.Error()))
+			return
+		}
+
+		targets := make([]*endpoint, 0)
+		for _, ep := range endpoints {
+			targets = append(targets, &endpoint{
+				Targets: []string{
+					fmt.Sprintf("%s:%d", ep.Hostname, ep.Port),
+				},
+				Labels: map[string]string{
+					"shard": ep.Shard,
+					"host":  ep.Hostname,
+				},
+			})
+		}
+
+		out, err := json.MarshalIndent(targets, "", "    ")
+		if err != nil {
+			w.WriteHeader(http.StatusInternalServerError)
+			w.Write([]byte(err.Error()))
+			return
+		}
+		w.Header().Set("content-type", "application/json")
+
+		w.Write(out)
+	})
+	server := &http.Server{
+		Addr:      fmt.Sprintf("[::1]:%d", *port),
+		TLSConfig: tlsConfig,
+		Handler:   loggingMiddleware.HandlerFunc(),
+	}
+
+	go server.ListenAndServeTLS("", "")
+
+	daemon.SdNotify(false, daemon.SdNotifyReady)
+
+	<-ctx.Done()
+	cancel()
+
+	shutdownCtx, _ := context.WithTimeout(context.Background(), 5*time.Second)
+	server.Shutdown(shutdownCtx)
+}
diff --git a/metrics/prometheus_http_discovery/systemd/prometheus-http-discovery.service b/metrics/prometheus_http_discovery/systemd/prometheus-http-discovery.service
new file mode 100644
index 0000000..9b63216
--- /dev/null
+++ b/metrics/prometheus_http_discovery/systemd/prometheus-http-discovery.service
@@ -0,0 +1,10 @@
+[Unit]
+Description=Prometheus HTTP endpoint discoverer monitors service discovery entries and returns Prometheus http_sd_config JSON
+
+[Service]
+Type=notify
+User=nobody
+ExecStart=/usr/bin/prometheus-http-discovery
+
+[Install]
+WantedBy=default.target
-- 
2.50.1