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Add ConfigMap Examples
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‎13-ConfigMaps/README.md

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## ConfigMap
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> [Updating Configuration via a ConfigMap](https://kubernetes.io/docs/tutorials/configuration/updating-configuration-via-a-configmap/)
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> [!IMPORTANT]
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> Although the value of the **key inside the ConfigMap has changed, the environment variable in the Pod still shows the earlier value**. This is because environment variables for a process running inside a Pod are **not** updated when the source data changes; if you wanted to force an update, you would need to have Kubernetes replace your existing Pods. The new Pods would then run with the updated information.
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**Solutions**:
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1. Use `kubectl rollout restart`
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This will cause the pods to reload with the new environment variables and configuration.
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Files:
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- [Deployment](./deployment.yaml)
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- [ConfigMap](./configmap.yaml)
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- [NodePort Service](./service.yaml)
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```bash
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kubectl rollout restart deployment <deployment-name>
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```
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![Image](./images/img-1.webp)
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2. Use `envFrom` to Load ConfigMap as Volume
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If you want to have more flexibility and allow the pod to pick up updates from the `ConfigMap` without a restart, you can mount the `ConfigMap` as a volume.
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Files:
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- [Deployment](./deployment-2.yaml)
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- [ConfigMap](./configmap-2.yaml)
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- [NodePort Service](./service-2.yaml)
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![Image](./images/img-2.webp)

‎13-ConfigMaps/app/Dockerfile

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# Stage 1: Build
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FROM golang:alpine AS builder
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ENV CGO_ENABLED=0 GOOS=linux
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WORKDIR /app
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COPY . .
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RUN go build -o server .
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# Stage 2: Run
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FROM scratch
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WORKDIR /root/
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COPY --from=builder /app/server .
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EXPOSE 8080
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CMD ["./server"]

‎13-ConfigMaps/app/go.mod

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module github.com/nmdra/K8s-Learn/13-ConfigMaps/app
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go 1.23.4

‎13-ConfigMaps/app/main.go

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package main
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import (
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"html/template"
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"log"
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"net"
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"net/http"
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"os"
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"strings"
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)
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type PageData struct {
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EnvVars map[string]string
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ConfigVars map[string]string
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Hostname string
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IPAddress string
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}
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func main() {
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log.Println("Starting the server on port 8080")
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http.HandleFunc("/", handler)
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log.Fatal(http.ListenAndServe(":8080", nil)) // Log fatal errors if server fails
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}
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func handler(w http.ResponseWriter, r *http.Request) {
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log.Printf("Received request from %s %s\n", r.RemoteAddr, r.Method)
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envVars := os.Environ()
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envMap := make(map[string]string)
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for _, env := range envVars {
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parts := strings.SplitN(env, "=", 2)
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if len(parts) == 2 {
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envMap[parts[0]] = parts[1]
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}
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}
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log.Println("Fetched environment variables")
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configVars := readConfigFiles("/etc/config")
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log.Printf("Fetched %d config variables\n", len(configVars))
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host, ip := getHostIP()
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log.Printf("Fetched hostname: %s, IP address: %s\n", host, ip)
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data := PageData{
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EnvVars: envMap,
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ConfigVars: configVars,
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Hostname: host,
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IPAddress: ip,
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}
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renderTemplate(w, data)
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}
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func renderTemplate(w http.ResponseWriter, data PageData) {
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tmpl := `
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<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="UTF-8">
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<meta name="viewport" content="width=device-width, initial-scale=1.0">
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<title>Environment and Config Variables</title>
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<style>
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body {
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font-family: Arial, sans-serif;
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margin: 2em;
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background-color: #f4f4f9;
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}
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h1 {
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color: #333;
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}
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.container {
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background: #fff;
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padding: 20px;
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border-radius: 8px;
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box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
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}
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.value {
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color: #007BFF;
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font-weight: bold;
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}
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.env-table {
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width: 100%;
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border-collapse: collapse;
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margin-top: 1em;
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}
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.env-table th, .env-table td {
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border: 1px solid #ddd;
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padding: 8px;
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}
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.env-table th {
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background-color: #f4f4f9;
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text-align: left;
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}
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</style>
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</head>
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<body>
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<div class="container">
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<h1>Environment and Config Variable Viewer</h1>
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<p><strong>Hostname:</strong> <span class="value">{{.Hostname}}</span></p>
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<p><strong>IP Address:</strong> <span class="value">{{.IPAddress}}</span></p>
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<h2>Environment Variables</h2>
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<table class="env-table">
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<tr>
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<th>Key</th>
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<th>Value</th>
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</tr>
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{{range $key, $value := .EnvVars}}
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<tr>
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<td>{{$key}}</td>
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<td>{{$value}}</td>
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</tr>
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{{end}}
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</table>
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<h2>Config Variables (from ConfigMap Volume)</h2>
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<table class="env-table">
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<tr>
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<th>Key</th>
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<th>Value</th>
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</tr>
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{{range $key, $value := .ConfigVars}}
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<tr>
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<td>{{$key}}</td>
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<td>{{$value}}</td>
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</tr>
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{{end}}
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</table>
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</div>
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</body>
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</html>
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`
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t := template.Must(template.New("webpage").Parse(tmpl))
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err := t.Execute(w, data)
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if err != nil {
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log.Printf("Error rendering template: %v\n", err)
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http.Error(w, "Failed to render template", http.StatusInternalServerError)
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}
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}
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func readConfigFiles(configDir string) map[string]string {
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configVars := make(map[string]string)
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log.Printf("Reading config files from directory: %s\n", configDir)
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files, err := os.ReadDir(configDir)
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if err != nil {
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log.Printf("Error reading config directory: %v\n", err)
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return configVars // Return empty map if error occurs
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}
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for _, file := range files {
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if !file.IsDir() {
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content, err := os.ReadFile(configDir + "/" + file.Name())
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if err == nil {
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configVars[file.Name()] = string(content)
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log.Printf("Loaded config file: %s\n", file.Name())
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} else {
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log.Printf("Error reading config file %s: %v\n", file.Name(), err)
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}
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}
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}
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return configVars
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}
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func getHostIP() (string, string) {
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host, err := os.Hostname()
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if err != nil {
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log.Printf("Error getting hostname: %v\n", err)
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host = "Unknown"
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}
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addrs, err := net.InterfaceAddrs()
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if err != nil {
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log.Printf("Error getting network interface addresses: %v\n", err)
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return host, "Unknown"
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}
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for _, addr := range addrs {
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if ipNet, ok := addr.(*net.IPNet); ok && !ipNet.IP.IsLoopback() {
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if ipNet.IP.To4() != nil {
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log.Printf("Found IP address: %s\n", ipNet.IP.String())
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return host, ipNet.IP.String()
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}
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}
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}
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return host, "Unknown"
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}

‎13-ConfigMaps/configmap-2.yaml

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apiVersion: v1
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kind: ConfigMap
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metadata:
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name: new-config
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namespace: default
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data:
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NEW_MESSAGE: "Hello from Volume!"
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NEW_ENV: "Volume"

‎13-ConfigMaps/configmap.yaml

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apiVersion: v1
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kind: ConfigMap
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metadata:
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name: app-config
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namespace: default
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data:
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APP_MESSAGE: "Hello from ConfigMap!"
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AUTHOR: "NIMENDRA"
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NEW_ENV: "K3s"

‎13-ConfigMaps/deployment-2.yaml

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apiVersion: apps/v1
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kind: Deployment
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metadata:
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name: env-reader-2
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namespace: default
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spec:
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replicas: 3
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selector:
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matchLabels:
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app: env-reader-2
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template:
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metadata:
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labels:
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app: env-reader-2
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spec:
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containers:
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- name: env-reader-2
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image: ghcr.io/nmdra/k8s-learn/env-reader:2.0
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imagePullPolicy: IfNotPresent
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ports:
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- containerPort: 8080
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envFrom:
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- configMapRef:
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name: app-config
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volumeMounts:
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- name: config-volume
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mountPath: /etc/config
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readOnly: true
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volumes:
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- name: config-volume
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configMap:
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name: new-config

‎13-ConfigMaps/deployment.yaml

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apiVersion: apps/v1
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kind: Deployment
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metadata:
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name: env-reader-deployment
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namespace: default
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spec:
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replicas: 2
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selector:
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matchLabels:
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app: env-reader
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template:
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metadata:
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labels:
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app: env-reader
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spec:
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containers:
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- name: env-reader
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image: ghcr.io/nmdra/k8s-learn/env-reader:2.0
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ports:
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- containerPort: 8080
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envFrom:
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- configMapRef:
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name: app-config

‎13-ConfigMaps/images/img-1.webp

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‎13-ConfigMaps/images/img-2.webp

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‎13-ConfigMaps/service-2.yaml

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apiVersion: v1
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kind: Service
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metadata:
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name: env-reader-service-2
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namespace: default
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spec:
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selector:
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app: env-reader-2
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ports:
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- protocol: TCP
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port: 80
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targetPort: 8080
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nodePort: 30088
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type: NodePort

‎13-ConfigMaps/service.yaml

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apiVersion: v1
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kind: Service
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metadata:
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name: env-reader-service
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namespace: default
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spec:
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selector:
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app: env-reader
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ports:
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- protocol: TCP
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port: 80
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targetPort: 8080
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nodePort: 30080
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type: NodePort

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