OCPBUGS-14891: Initialize the most likely labels for the metrics

Author: machine424

README.md

@@ -4,7 +4,7 @@ This example app serves as an example of how one can easily instrument HTTP hand
 
 Usage is simple, on any request to `/` the request will result in a `200` response code. This increments the counter for this response code. Similarly the `/err` endpoint will result in a `404` response code, therefore increments that respective counter. Duration metrics are also exposed for any request to `/`.
 
-A Docker image is available at: `ghcr.io/rhobs/prometheus-example-app:0.3.0`
+A Docker image is available at: `ghcr.io/rhobs/prometheus-example-app`
 
 ## Deploying in a Kubernetes cluster
 
@@ -33,7 +33,7 @@ The following metrics are exposed:
 
 The sample output of the `/metric` endpoint after 5 incoming HTTP requests shown below.
 
-Note: with no initial incoming request, only `version` metric is reported.
+Note: In addition to `version`, the other metrics are initialized with the most likely labels.
 
 ```
 # HELP http_request_duration_seconds Duration of all HTTP requests

VERSION

@@ -1 +1 @@
-v0.4.1
+v0.4.2

main.go

@@ -12,6 +12,8 @@ import (
 	"golang.org/x/net/http2/h2c"
 )
 
+const foundHandlerName = "found"
+
 var (
 	appVersion string
 	version    = prometheus.NewGauge(prometheus.GaugeOpts{
@@ -47,6 +49,11 @@ func main() {
 	r.MustRegister(httpRequestDuration)
 	r.MustRegister(version)
 
+	// Initialize the most likely labels.
+	httpRequestDuration.WithLabelValues("200", foundHandlerName, "get")
+	httpRequestsTotal.WithLabelValues("200", "get")
+	httpRequestsTotal.WithLabelValues("404", "get")
+
 	foundHandler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(http.StatusOK)
 		w.Write([]byte("Hello from example application."))
@@ -56,7 +63,7 @@ func main() {
 	})
 
 	foundChain := promhttp.InstrumentHandlerDuration(
-		httpRequestDuration.MustCurryWith(prometheus.Labels{"handler": "found"}),
+		httpRequestDuration.MustCurryWith(prometheus.Labels{"handler": foundHandlerName}),
 		promhttp.InstrumentHandlerCounter(httpRequestsTotal, foundHandler),
 	)
 

manifests/deployment.yaml

@@ -16,7 +16,7 @@ spec:
     spec:
       containers:
       - name: prometheus-example-app
-        image: ghcr.io/rhobs/prometheus-example-app:0.3.0
+        image: ghcr.io/rhobs/prometheus-example-app:latest
         ports:
         - name: web
           containerPort: 8080