added healthcheck

implemented flag for http checking health endpoint

Dockerfile

@@ -36,9 +36,6 @@ RUN CGO_ENABLED=0 go build \
         -X main.BuildDate=$(date -u ""+%Y%m%d-%H:%M:%S"")" \
     -o /app .
 
-# Second stage: get statically linked curl
-FROM wmark/curl:latest as curl
-
 # Final stage: the running container.
 FROM scratch AS final
 
@@ -54,9 +51,6 @@ COPY --from=builder /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/
 # Import the compiled executable from the first stage.
 COPY --from=builder /app /app
 
-# Get curl from image
-COPY --from=curl /usr/bin/curl /usr/bin/curl
-
 # Declare the port on which the webserver will be exposed.
 # As we're going to run the executable as an unprivileged user, we can't bind
 # to ports below 1024.
@@ -66,6 +60,6 @@ EXPOSE 9419
 USER nobody:nobody
 
 # Check if exporter is alive; 10 retries gives prometheus some time to retrieve bad data (5 minutes)
-HEALTHCHECK --retries=10 CMD "/usr/bin/curl -s -f http://localhost:9419/health || exit 1"]
+HEALTHCHECK --retries=10 CMD ["/app", "-check-url", "http://localhost:9419/health"]
 # Run the compiled binary.
 ENTRYPOINT ["/app"]

curl.go

@@ -0,0 +1,25 @@
+package main
+
+import (
+	"fmt"
+	"net/http"
+	"os"
+	"time"
+)
+
+// curl like check for an http url.
+// used inside docker image for checking health endpoint
+// will os.Exit(0) for http response code 200. Otherwise os.Exit(1)
+func curl(url string) {
+	var client = &http.Client{Timeout: 30 * time.Second}
+	resp, err := client.Get(url)
+	if err != nil {
+		fmt.Printf("Error checking url: %v\n", err)
+		os.Exit(1)
+	}
+	if resp.StatusCode != http.StatusOK {
+		fmt.Printf("Error checking url: Unexpected http code %v\n", resp.StatusCode)
+		os.Exit(1)
+	}
+	os.Exit(0)
+}

exporter.go

@@ -49,7 +49,6 @@ type exporter struct {
 type Exporter interface {
 	Collect(ctx context.Context, ch chan<- prometheus.Metric) error
 	Describe(ch chan<- *prometheus.Desc)
-	LastScrapeOK() bool
 }
 
 func newExporter() *exporter {

main.go

@@ -31,10 +31,15 @@ func initLogger() {
 }
 
 func main() {
-
+	var checkURL = flag.String("check-url", "", "Curl url and return exit code (http: 200 => 0, otherwise 1)")
 	var configFile = flag.String("config-file", "conf/rabbitmq.conf", "path to json config")
 	flag.Parse()
 
+	if *checkURL != "" { // do a single http get request. Used in docker healthckecks as curl is not inside the image
+		curl(*checkURL)
+		return
+	}
+
 	err := initConfigFromFile(*configFile)                  //Try parsing config file
 	if _, isPathError := err.(*os.PathError); isPathError { // No file => use environment variables
 		initConfig()