From afbd8b8b4584cc7bfc4ce947252883f5cd443402 Mon Sep 17 00:00:00 2001
From: Wimo <wimo@wimodya-athukorala.com>
Date: Wed, 21 Jul 2021 20:45:09 +0800
Subject: [PATCH] Ability to scrape dynamic targets

Signed-off-by: Wimo <wimo@wimodya-athukorala.com>
---
 cmd/postgres_exporter/main.go | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/cmd/postgres_exporter/main.go b/cmd/postgres_exporter/main.go
index 25f94a745..3e32b5b3f 100644
--- a/cmd/postgres_exporter/main.go
+++ b/cmd/postgres_exporter/main.go
@@ -14,6 +14,7 @@
 package main
 
 import (
+	"context"
 	"net/http"
 	"os"
 
@@ -115,6 +116,12 @@ func main() {
 	prometheus.MustRegister(exporter)
 
 	http.Handle(*metricPath, promhttp.Handler())
+
+	registries := make(map[string]*prometheus.Registry)
+	http.HandleFunc("/probe", func(w http.ResponseWriter, req *http.Request) {
+		probeHandler(w, req, logger, registries, opts...)
+	})
+
 	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Content-Type", "text/html; charset=UTF-8") // nolint: errcheck
 		w.Write(landingPage)                                       // nolint: errcheck
@@ -127,3 +134,29 @@ func main() {
 		os.Exit(1)
 	}
 }
+
+func probeHandler(w http.ResponseWriter, r *http.Request, logger log.Logger, registries map[string]*prometheus.Registry, opts ...ExporterOpt) {
+
+	ctx, cancel := context.WithCancel(r.Context())
+	defer cancel()
+	r = r.WithContext(ctx)
+
+	target := r.URL.Query().Get("target")
+	if target == "" {
+		http.Error(w, "Target parameter is missing", http.StatusBadRequest)
+		return
+	}
+
+	registry, target_registered := registries[target]
+	if !target_registered {
+		registry = prometheus.NewPedanticRegistry()
+		exporter := NewExporter([]string{target}, opts...)
+		registry.MustRegister(version.NewCollector(exporterName))
+		registry.MustRegister(exporter)
+		registries[target] = registry
+	}
+
+	h := promhttp.HandlerFor(registry, promhttp.HandlerOpts{})
+	h.ServeHTTP(w, r)
+
+}