feat: add health endpoint to exporter (!110)

* Add new `/health` endpoint to check if exporter is running correctly
* Update docker healthcheck to use the new endpoint

https://gitlab.com/hectorjsmith/fail2ban-prometheus-exporter/-/merge_requests/110

Dockerfile

@@ -6,10 +6,10 @@ WORKDIR /app
 # Copy compiled binary to release image
 # (must build the binary before running docker build)
 COPY fail2ban_exporter /app/fail2ban_exporter
-COPY health /app/health
 
 # Setup a healthcheck
+COPY health /app/health
 RUN apk add curl
-HEALTHCHECK --interval=10s --timeout=4s CMD /app/health
+HEALTHCHECK --interval=10s --timeout=4s --retries=3 CMD /app/health
 
 ENTRYPOINT ["/app/fail2ban_exporter"]

collector/f2b/collector.go

@@ -61,6 +61,22 @@ func (c *Collector) Collect(ch chan<- prometheus.Metric) {
 	c.collectErrorCountMetric(ch)
 }
 
+func (c *Collector) IsHealthy() bool {
+	s, err := socket.ConnectToSocket(c.socketPath)
+	if err != nil {
+		log.Printf("error opening socket: %v", err)
+		c.socketConnectionErrorCount++
+		return false
+	}
+	pingSuccess, err := s.Ping()
+	if err != nil {
+		log.Printf("error pinging fail2ban server: %v", err)
+		c.socketRequestErrorCount++
+		return false
+	}
+	return pingSuccess
+}
+
 func printFail2BanServerVersion(socketPath string) {
 	s, err := socket.ConnectToSocket(socketPath)
 	if err != nil {

exporter.go

@@ -44,7 +44,7 @@ func main() {
 	prometheus.MustRegister(textFileCollector)
 
 	if !appSettings.DryRunMode {
-		svrErr := server.StartServer(appSettings, textFileCollector)
+		svrErr := server.StartServer(appSettings, f2bCollector, textFileCollector)
 		err := <-svrErr
 		log.Fatal(err)
 	} else {

health

@@ -5,4 +5,4 @@ if [ ! -z $F2B_WEB_LISTEN_ADDRESS ]; then
     port=`echo $F2B_WEB_LISTEN_ADDRESS | cut -d ":" -f 2 -`
 fi
 
-curl --fail localhost:$port/metrics || exit 1
+curl --fail localhost:$port/health || exit 1

server/handler.go

@@ -5,6 +5,7 @@ import (
 	"net/http"
 
 	"github.com/prometheus/client_golang/prometheus/promhttp"
+	"gitlab.com/hectorjsmith/fail2ban-prometheus-exporter/collector/f2b"
 	"gitlab.com/hectorjsmith/fail2ban-prometheus-exporter/collector/textfile"
 )
 
@@ -31,3 +32,13 @@ func metricHandler(w http.ResponseWriter, r *http.Request, collector *textfile.C
 	promhttp.Handler().ServeHTTP(w, r)
 	collector.WriteTextFileMetrics(w, r)
 }
+
+func healthHandler(w http.ResponseWriter, r *http.Request, collector *f2b.Collector) {
+	if collector.IsHealthy() {
+		w.WriteHeader(http.StatusOK)
+		w.Write([]byte("{\"healthy\":true}"))
+	} else {
+		w.WriteHeader(http.StatusInternalServerError)
+		w.Write([]byte("{\"healthy\":false}"))
+	}
+}

server/server.go

@@ -6,11 +6,13 @@ import (
 	"time"
 
 	"gitlab.com/hectorjsmith/fail2ban-prometheus-exporter/cfg"
+	"gitlab.com/hectorjsmith/fail2ban-prometheus-exporter/collector/f2b"
 	"gitlab.com/hectorjsmith/fail2ban-prometheus-exporter/collector/textfile"
 )
 
 func StartServer(
 	appSettings *cfg.AppSettings,
+	f2bCollector *f2b.Collector,
 	textFileCollector *textfile.Collector,
 ) chan error {
 	http.HandleFunc("/", AuthMiddleware(
@@ -23,6 +25,11 @@ func StartServer(
 		},
 		appSettings.AuthProvider,
 	))
+	http.HandleFunc("/health",
+		func(w http.ResponseWriter, r *http.Request) {
+			healthHandler(w, r, f2bCollector)
+		},
+	)
 	log.Printf("metrics available at '%s'", metricsPath)
 
 	svrErr := make(chan error)