Lab 12, bonus task

app_go/.gitignore

@@ -25,3 +25,6 @@
 go.work
 
 # End of https://www.toptal.com/developers/gitignore/api/go
+
+
+/persistent

app_go/Dockerfile

@@ -1,5 +1,7 @@
 FROM golang:1.22.0-alpine3.19 as builder
 
+RUN ["mkdir", "/empty-dir"]
+
 WORKDIR /usr/src/app/
 
 COPY go.mod *.go /usr/src/app/
@@ -16,6 +18,8 @@ COPY --from=0 /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/ca-certificates.
 
 EXPOSE 5000
 
+VOLUME /persistent
 COPY --from=builder /usr/src/app/catfact_webapp /
 USER 2004:2004
+COPY --from=builder --chown=2004:2004 /empty-dir /persistent
 ENTRYPOINT ["/catfact_webapp"]

app_go/main.go

@@ -1,17 +1,25 @@
 package main
 
 import (
+	"sync/atomic"
+	"encoding/binary"
+	"errors"
+	"path/filepath"
 	"fmt"
 	"log"
 	"net/http"
+	"os"
 	"time"
 
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promauto"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
 )
 
-func index(w http.ResponseWriter, r *http.Request) {
+const visitsFile = "persistent/visits.bin"
+var visits atomic.Uint64
+
+func indexHandler(w http.ResponseWriter, r *http.Request) {
 	fact, err := catFact()
 	if err == nil {
         w.WriteHeader(http.StatusOK)
@@ -22,6 +30,10 @@ func index(w http.ResponseWriter, r *http.Request) {
 	}
 }
 
+func visitsHandler(w http.ResponseWriter, r *http.Request) {
+	_, _ = fmt.Fprintf(w, "%d", visits.Load())
+}
+
 
 var (
 	reqCnt = promauto.NewCounter(prometheus.CounterOpts{
@@ -48,14 +60,42 @@ func noteTimeMiddleware(next http.Handler) http.Handler {
 	})
 }
 
+func countVisitsMiddleware(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		visits.Add(1)	// Atomic increment, no race condition here, so counter
+						// is always correct
+		buf := make([]byte, binary.MaxVarintLen64)
+		binary.LittleEndian.PutUint64(buf, visits.Load())
+		// Race condition in the order in which threads will write the file out,
+		// so the file may not be correct, but as the same number of bytes is
+		// always written out, the counter in the file remains a valid number.
+		os.WriteFile(visitsFile, buf, 0644)
+		next.ServeHTTP(w, r)
+	})
+}
+
+
+func init() {
+	_ = os.MkdirAll(filepath.Dir(visitsFile), 0755)
+	buf, err := os.ReadFile(visitsFile)
+	if err == nil {
+		visits.Store(binary.LittleEndian.Uint64(buf))
+	} else if errors.Is(err, os.ErrNotExist) {
+		visits.Store(0)
+	} else {
+		panic(err)
+	}
+}
+
 
 func main() {
 	businessLogic := http.NewServeMux()
-	businessLogic.Handle("/", asHandler(index))
+	businessLogic.Handle("/", asHandler(indexHandler))
+	businessLogic.Handle("/visits", asHandler(visitsHandler))
 	// Note: keeping /metrics under middleware too for consistency with app_py
 	businessLogic.Handle("/metrics", promhttp.Handler())
 
-	wrapped := noteTimeMiddleware(businessLogic)
+	wrapped := noteTimeMiddleware(countVisitsMiddleware(businessLogic))
 
 	hostPort := "0.0.0.0:5000"
 	_, _ = fmt.Println("Listening on http://" + hostPort)

k8s/app-go/files/config.yaml

@@ -0,0 +1,2 @@
+seal: "2001"
+monk_seal: "century"

k8s/app-go/templates/config-map.yaml

@@ -0,0 +1,6 @@
+apiVersion: "v1"
+kind: ConfigMap
+metadata:
+  name: {{.Release.Name}}-config-map
+data:
+{{ .Files.Get "files/config.yaml" | indent 2 }}

k8s/app-go/templates/deployment.yaml

@@ -51,7 +51,16 @@ spec:
             {{- toYaml . | nindent 12 }}
           {{- end }}
           env:
-            {{ include "app-go.environ" . | nindent 12 }}
+            - name: seal
+              valueFrom:
+                configMapKeyRef:
+                  name: {{.Release.Name}}-config-map
+                  key: seal
+            - name: monk_seal
+              valueFrom:
+                configMapKeyRef:
+                  name: {{.Release.Name}}-config-map
+                  key: monk_seal
       {{- with .Values.volumes }}
       volumes:
         {{- toYaml . | nindent 8 }}

k8s/app-go/values.yaml

@@ -4,7 +4,7 @@ image:
   repository: kolay0ne/app_go
   pullPolicy: IfNotPresent
   # Overrides the image tag whose default is the chart appVersion.
-  tag: "lab8"
+  tag: "lab12"
 
 serviceAccount:
   # Specifies whether a service account should be created

monitoring/docker-compose.yml

@@ -5,6 +5,7 @@ networks:
 volumes:
   grafana-storage:
   py-persistent:
+  go-persistent:
 
 services:
   app_py:
@@ -22,7 +23,7 @@ services:
       - py-persistent:/app/persistent
 
   app_go:
-    image: kolay0ne/app_go:lab8
+    image: kolay0ne/app_go:lab12
     ports:
       - "5500:5000"
     logging:
@@ -32,6 +33,8 @@ services:
       resources: {limits: {memory: 20M}}
     networks:
       - prometheus
+    volumes:
+      - go-persistent:/persistent
 
   loki:
     image: grafana/loki:2.9.2