cleanup and README

Signed-off-by: Joe Adams <github@joeadams.io>

Co-authored-by: Ben Kochie <superq@gmail.com>

README.md

@@ -21,6 +21,36 @@ docker run \
   quay.io/prometheuscommunity/postgres-exporter
 ```
 
+## Multi-Target Support (BETA)
+**This Feature is in beta and may require changes in future releases. Feedback is welcome.**
+
+This exporter supports the [multi-target pattern](https://prometheus.io/docs/guides/multi-target-exporter/). This allows running a single instance of this exporter for multiple postgres targets. Using the milti-target funcationality of this exporter is **optional** and meant for users where it is impossible to install the exporter as a sidecar. For example SaaS-managed services.
+
+To use the multi-target functionality, send an http request to the endpoint `/probe?target=foo:5432` where target is set to the DSN of the postgres instance to scrape metrics from.
+
+To avoid putting sensitive information like username and password in the URL, preconfigured auth modules are supported via the [auth_modules](#auth_modules) section of the config file. auth_modules for DSNs can be used with the `/probe` endpoint by specifying the `?auth_module=foo` http parameter.
+
+## Configuration File
+
+The configuration file controls the behavior of the exporter. It can be set using the `--config.file` command line flag and defaults to `postres_exporter.yml`.
+
+### auth_modules
+This section defines preset authentication and connection parameters for use in the [multi-target endpoint](#multi-target-support-beta). `auth_modules` is a map of modules with the key being the identifier which can be used in the `/probe` endpoint.
+Currently only the `userpass` type is supported.
+
+Example:
+```yaml
+auth_modules:
+  foo1: # Set this to any name you want
+    type: userpass
+    userpass:
+      username: first
+      password: firstpass
+    options:
+      # options become key=value parameters of the DSN
+      sslmode: disable
+```
+
 ## Building and running
 
     git clone https://github.com/prometheus-community/postgres_exporter.git

cmd/postgres_exporter/main.go

@@ -102,12 +102,6 @@ func main() {
 		os.Exit(1)
 	}
 
-	// TODO(@sysadmind): Remove this with multi-target support
-	// if len(dsn) == 0 {
-	// 	level.Error(logger).Log("msg", "Couldn't find environment variables describing the datasource to use")
-	// 	os.Exit(1)
-	// }
-
 	opts := []ExporterOpt{
 		DisableDefaultMetrics(*disableDefaultMetrics),
 		DisableSettingsMetrics(*disableSettingsMetrics),

cmd/postgres_exporter/probe.go

@@ -60,7 +60,7 @@ func handleProbe(logger log.Logger) http.HandlerFunc {
 			return
 		}
 
-		// TODO: Timeout
+		// TODO(@sysadmind): Timeout
 
 		probeSuccessGauge := prometheus.NewGauge(prometheus.GaugeOpts{
 			Name: "probe_success",
@@ -86,23 +86,15 @@ func handleProbe(logger log.Logger) http.HandlerFunc {
 			http.Error(w, err.Error(), http.StatusInternalServerError)
 			return
 		}
+
+		// TODO(@sysadmind): Remove the registry.MustRegister() call below and instead handle the collection here. That will allow
+		// for the passing of context, handling of timeouts, and more control over the collection.
+		// The current NewProbeCollector() implementation relies on the MustNewConstMetric() call to create the metrics which is not
+		// ideal to use without the registry.MustRegister() call.
 		_ = ctx
 
-		// TODO: Which way should this be? Register or handle the collection manually?
-		// Also, what about the context?
-
-		// Option 1: Register the collector
 		registry.MustRegister(pc)
 
-		// Option 2: Handle the collection manually. This allows us to collect duration metrics.
-		// The collectors themselves already support their own duration metrics.
-		// err = pc.Update(ctx)
-		// if err != nil {
-		// 	probeSuccessGauge.Set(0)
-		// } else {
-		// 	probeSuccessGauge.Set(1)
-		// }
-
 		duration := time.Since(start).Seconds()
 		probeDurationGauge.Set(duration)
 

config/config.go

@@ -22,28 +22,24 @@ import (
 
 	"github.com/go-kit/log"
 	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
 	"gopkg.in/yaml.v3"
 )
 
 var (
-	configReloadSuccess = prometheus.NewGauge(prometheus.GaugeOpts{
+	configReloadSuccess = promauto.NewGauge(prometheus.GaugeOpts{
 		Namespace: "postgres_exporter",
 		Name:      "config_last_reload_successful",
 		Help:      "Postgres exporter config loaded successfully.",
 	})
 
-	configReloadSeconds = prometheus.NewGauge(prometheus.GaugeOpts{
+	configReloadSeconds = promauto.NewGauge(prometheus.GaugeOpts{
 		Namespace: "postgres_exporter",
 		Name:      "config_last_reload_success_timestamp_seconds",
 		Help:      "Timestamp of the last successful configuration reload.",
 	})
 )
 
-func init() {
-	prometheus.MustRegister(configReloadSuccess)
-	prometheus.MustRegister(configReloadSeconds)
-}
-
 type Config struct {
 	AuthModules map[string]AuthModule `yaml:"auth_modules"`
 }