feat: add http endpoint for reloading config

The added endpoint `/-/reload` triggers a reload of the redfish_exporter
configuration when receiving a PUT or POST request.

Author: Mehdi Yedes

README.md

@@ -58,7 +58,17 @@ curl http://<redfish_exporter host>:9610/redfish?target=10.36.48.24
 ```
 or by pointing your favourite browser at this URL.
 
-## prometheus configuration
+## Reloading Configuration
+```
+PUT /-/reload
+POST /-/reload
+```
+The `/-/reload` endpoint triggers a reload of the redfish_exporter configuration.
+500 will be returned when the reload fails.
+
+Alternatively, a configuration reload can be triggered by sending `SIGHUP` to the redfish_exporter process as well.
+
+## Prometheus Configuration
 
 You can then setup [Prometheus][3] to scrape the target using
 something like this in your Prometheus configuration files:

main.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"io"
 	"net/http"
 	"os"
 	"os/signal"
@@ -45,6 +46,25 @@ func init() {
 	rootLoggerCtx.Infof("version %s, build reversion %s, build branch %s, build at %s on host %s", Version, BuildRevision, BuildBranch, BuildTime, hostname)
 }
 
+func reloadHandler(configLoggerCtx *alog.Entry) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		if r.Method == "POST" || r.Method == "PUT" {
+			configLoggerCtx.Info("Triggered configuration reload from /-/reload HTTP endpoint")
+			err := sc.ReloadConfig(*configFile)
+			if err != nil {
+				configLoggerCtx.WithError(err).Error("failed to reload config file")
+				http.Error(w, "failed to reload config file", http.StatusInternalServerError)
+			}
+			configLoggerCtx.WithField("operation", "sc.ReloadConfig").Info("config file reloaded")
+
+			w.WriteHeader(http.StatusOK)
+			io.WriteString(w, "Configuration reloaded successfully!")
+		} else {
+			http.Error(w, "Only PUT and POST methods are allowed", http.StatusBadRequest)
+		}
+	}
+}
+
 // define new http handleer
 func metricsHandler() http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
@@ -136,7 +156,8 @@ func main() {
 		}
 	}()
 
-	http.Handle("/redfish", metricsHandler()) // Regular metrics endpoint for local Redfish metrics.
+	http.Handle("/redfish", metricsHandler())                // Regular metrics endpoint for local Redfish metrics.
+	http.Handle("/-/reload", reloadHandler(configLoggerCtx)) // HTTP endpoint for triggering configuration reload
 	http.Handle("/metrics", promhttp.Handler())
 
 	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {