Implement hot reload

Makefile

@@ -32,6 +32,10 @@ out/main-%:
 run:
 	go run cmd/exporter/main.go
 
+#: Runs the Go Exporter application with watching the configuration file
+run-and-watch-config:
+	go run cmd/exporter/main.go -watch
+
 #: Builds a binary executable for Linux
 build-linux: out/main-linux
 #: Builds a binary executable for Darwin

README.md

@@ -158,6 +158,7 @@ See more in the [Migration](#migration) section.
 
 - `make all`: Builds binary executables for all OS (Win, Darwin, Linux).
 - `make run`: Runs the Go Exporter application.
+- `make run-and-watch-config`: Runs the Go Exporter application with watching the configuration file.
 - `make build-linux`: Builds a binary executable for Linux.
 - `make build-darwin`: Builds a binary executable for Darwin.
 - `make build-windows`: Builds a binary executable for Windows.

cmd/exporter/main.go

@@ -1,81 +1,34 @@
 package main
 
 import (
-	"flag"
-	"fmt"
-	"log"
+	"context"
 	"log/slog"
 	"os"
-	"strconv"
 
-	"github.com/joho/godotenv"
-	"github.com/prometheus/client_golang/prometheus"
-
-	"github.com/kuskoman/logstash-exporter/internal/server"
-	"github.com/kuskoman/logstash-exporter/pkg/config"
-	"github.com/kuskoman/logstash-exporter/pkg/manager"
+	"github.com/kuskoman/logstash-exporter/internal/flags"
+	"github.com/kuskoman/logstash-exporter/internal/startup_manager"
 )
 
 func main() {
-	versionFlag := flag.Bool("version", false, "prints the version and exits")
-	helpFlag := flag.Bool("help", false, "prints the help message and exits")
-	configLocationFlag := flag.String("config", config.ExporterConfigLocation, "location of the exporter config file")
-
-	flag.Parse()
-
-	if *helpFlag {
-		fmt.Printf("Usage of %s:\n", os.Args[0])
-		fmt.Println()
-		fmt.Println("Flags:")
-		flag.PrintDefaults()
+	flagsConfig, err := flags.ParseFlags(os.Args[1:])
+	if err != nil {
+		slog.Error("failed to parse flags", "err", err)
 		return
 	}
 
-	if *versionFlag {
-		fmt.Printf("%s\n", config.SemanticVersion)
-		return
+	if shouldExit := flags.HandleFlags(flagsConfig); shouldExit {
+		os.Exit(0)
 	}
 
-	warn := godotenv.Load()
-
-	exporterConfig, err := config.GetConfig(*configLocationFlag)
+	startupManager, err := startup_manager.NewStartupManager(flagsConfig.ConfigLocation, flagsConfig)
 	if err != nil {
-		log.Fatalf("failed to get exporter config: %s", err)
+		slog.Error("failed to create startup manager", "err", err)
 		os.Exit(1)
 	}
 
-	logger, err := config.SetupSlog(exporterConfig.Logging.Level, exporterConfig.Logging.Format)
-	if err != nil {
-		log.Printf("failed to load .env file: %s", err)
-		log.Fatalf("failed to setup slog: %s", err)
-	}
-
-	slog.SetDefault(logger)
-
-	if warn != nil {
-		slog.Warn("failed to load .env file", "error", warn)
-	}
-
-	host := exporterConfig.Server.Host
-	port := strconv.Itoa(exporterConfig.Server.Port)
-
-	slog.Debug("application starting... ")
-	versionInfo := config.GetVersionInfo()
-	slog.Info(versionInfo.String())
-
-	slog.Debug("http timeout", "timeout", exporterConfig.Logstash.HttpTimeout)
-
-	collectorManager := manager.NewCollectorManager(
-		exporterConfig.Logstash.Servers,
-		exporterConfig.Logstash.HttpTimeout,
-	)
-	prometheus.MustRegister(collectorManager)
-
-	appServer := server.NewAppServer(host, port, exporterConfig, exporterConfig.Logstash.HttpTimeout)
-
-	slog.Info("starting server on", "host", host, "port", port)
-	if err := appServer.ListenAndServe(); err != nil {
-		slog.Error("failed to listen and serve", "err", err)
+	ctx := context.TODO()
+	if err := startupManager.Initialize(ctx); err != nil {
+		slog.Error("critical error", "error", err)
 		os.Exit(1)
 	}
 }

go.mod

@@ -3,15 +3,15 @@ module github.com/kuskoman/logstash-exporter
 go 1.23
 
 require (
-	github.com/joho/godotenv v1.5.1
+	github.com/fsnotify/fsnotify v1.7.0
 	github.com/prometheus/client_golang v1.20.5
 	gopkg.in/yaml.v2 v2.4.0
 )
 
 require (
 	github.com/gkampitakis/ciinfo v0.3.0 // indirect
 	github.com/gkampitakis/go-diff v1.3.2 // indirect
-	github.com/klauspost/compress v1.17.10 // indirect
+	github.com/klauspost/compress v1.17.11 // indirect
 	github.com/kr/pretty v0.3.1 // indirect
 	github.com/kr/text v0.2.0 // indirect
 	github.com/maruel/natural v1.1.1 // indirect

go.sum

@@ -5,6 +5,8 @@ github.com/cespare/xxhash/v2 v2.3.0/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XL
 github.com/creack/pty v1.1.9/go.mod h1:oKZEueFk5CKHvIhNR5MUki03XCEU+Q6VDXinZuGJ33E=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/fsnotify/fsnotify v1.7.0 h1:8JEhPFa5W2WU7YfeZzPNqzMP6Lwt7L2715Ggo0nosvA=
+github.com/fsnotify/fsnotify v1.7.0/go.mod h1:40Bi/Hjc2AVfZrqy+aj+yEI+/bRxZnMJyTJwOpGvigM=
 github.com/gkampitakis/ciinfo v0.3.0 h1:gWZlOC2+RYYttL0hBqcoQhM7h1qNkVqvRCV1fOvpAv8=
 github.com/gkampitakis/ciinfo v0.3.0/go.mod h1:1NIwaOcFChN4fa/B0hEBdAb6npDlFL8Bwx4dfRLRqAo=
 github.com/gkampitakis/go-diff v1.3.2 h1:Qyn0J9XJSDTgnsgHRdz9Zp24RaJeKMUHg2+PDZZdC4M=
@@ -13,10 +15,8 @@ github.com/gkampitakis/go-snaps v0.5.7 h1:uVGjHR4t4pPHU944udMx7VKHpwepZXmvDMF+yD
 github.com/gkampitakis/go-snaps v0.5.7/go.mod h1:ZABkO14uCuVxBHAXAfKG+bqNz+aa1bGPAg8jkI0Nk8Y=
 github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
 github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
-github.com/joho/godotenv v1.5.1 h1:7eLL/+HRGLY0ldzfGMeQkb7vMd0as4CfYvUVzLqw0N0=
-github.com/joho/godotenv v1.5.1/go.mod h1:f4LDr5Voq0i2e/R5DDNOoa2zzDfwtkZa6DnEwAbqwq4=
-github.com/klauspost/compress v1.17.10 h1:oXAz+Vh0PMUvJczoi+flxpnBEPxoER1IaAnU/NMPtT0=
-github.com/klauspost/compress v1.17.10/go.mod h1:pMDklpSncoRMuLFrf1W9Ss9KT+0rH90U12bZKk7uwG0=
+github.com/klauspost/compress v1.17.11 h1:In6xLpyWOi1+C7tXUUWv2ot1QvBjxevKAaI6IXrJmUc=
+github.com/klauspost/compress v1.17.11/go.mod h1:pMDklpSncoRMuLFrf1W9Ss9KT+0rH90U12bZKk7uwG0=
 github.com/kr/pretty v0.3.1 h1:flRD4NNwYAUpkphVc1HcthR4KEIFJ65n8Mw5qdRn3LE=
 github.com/kr/pretty v0.3.1/go.mod h1:hoEshYVHaxMs3cyo3Yncou5ZscifuDolrwPKZanG3xk=
 github.com/kr/text v0.2.0 h1:5Nx0Ya0ZqY2ygV366QzturHI13Jq95ApcVaJBhpS+AY=

internal/file_utils/file_test_utils.go

@@ -0,0 +1,90 @@
+package file_utils
+
+import (
+	"os"
+	"testing"
+	"time"
+)
+
+func CreateTempFileInDir(t *testing.T, content, dir string) string {
+	t.Helper()
+
+	tempFile, err := os.CreateTemp(dir, "testfile")
+	if err != nil {
+		t.Fatalf("failed to create temp file: %v", err)
+	}
+
+	if _, err := tempFile.WriteString(content); err != nil {
+		tempFile.Close()
+		t.Fatalf("failed to write to temp file: %v", err)
+	}
+
+	if err := tempFile.Close(); err != nil {
+		t.Fatalf("failed to close temp file: %v", err)
+	}
+
+	return tempFile.Name()
+}
+
+func AppendToFilex3(t *testing.T, file, content string) {
+	t.Helper()
+	// ************ Add a content three times to make sure its written ***********
+	f, err := os.OpenFile(file, os.O_APPEND | os.O_WRONLY, 0644)
+	if err != nil {
+		t.Fatalf("failed to open a file: %v", err)
+	}
+
+	defer f.Close()
+
+	if err := f.Sync(); err != nil {
+		t.Fatalf("failed to sync file: %v", err)
+	}
+
+	if _, err := f.Write([]byte(content)); err != nil {
+		f.Close() // ignore error; Write error takes precedence
+		t.Fatalf("failed to write to file: %v", err)
+	}
+	if err := f.Sync(); err != nil {
+		t.Fatalf("failed to sync file: %v", err)
+	}
+
+	time.Sleep(50 * time.Millisecond) // give system time to sync write change before delete
+	if _, err := f.Write([]byte(content)); err != nil {
+		f.Close() // ignore error; Write error takes precedence
+		t.Fatalf("failed to write to file: %v", err)
+	}
+
+	if err := f.Sync(); err != nil {
+		t.Fatalf("failed to sync file: %v", err)
+	}
+	time.Sleep(50 * time.Millisecond) // give system time to sync write change before delete
+	if _, err := f.Write([]byte(content)); err != nil {
+		f.Close() // ignore error; Write error takes precedence
+		t.Fatalf("failed to write to file: %v", err)
+	}
+	if err := f.Sync(); err != nil {
+		t.Fatalf("failed to sync file: %v", err)
+	}
+}
+
+// CreateTempFile creates a temporary file with the given content and returns the path to it.
+func CreateTempFile(t *testing.T, content string) string {
+	return CreateTempFileInDir(t, content, "")
+}
+
+func RemoveDir(t *testing.T, path string) {
+	t.Helper()
+
+	if err := os.RemoveAll(path); err != nil {
+		t.Errorf("failed to remove temp file: %v", err)
+	}
+}
+
+// RemoveFile removes the file at the given path.
+func RemoveFile(t *testing.T, path string) {
+	t.Helper()
+
+	if err := os.Remove(path); err != nil {
+		t.Errorf("failed to remove temp file: %v", err)
+	}
+}

internal/file_utils/file_test_utils_test.go

@@ -0,0 +1,131 @@
+package file_utils
+
+import (
+	"os"
+	"testing"
+)
+
+func TestCreateTempFile(t *testing.T) {
+	t.Run("creates temporary file with given content", func(t *testing.T) {
+		content := "hello world"
+		path := CreateTempFile(t, content)
+		defer RemoveFile(t, path)
+
+		// Check if the file exists
+		if _, err := os.Stat(path); os.IsNotExist(err) {
+			t.Fatalf("expected file to exist, but it does not: %v", err)
+		}
+
+		// Read the file content and verify it matches
+		readContent, err := os.ReadFile(path)
+		if err != nil {
+			t.Fatalf("failed to read temp file: %v", err)
+		}
+
+		if string(readContent) != content {
+			t.Errorf("expected file content to be '%s', got '%s'", content, string(readContent))
+		}
+	})
+}
+
+func TestCreateTempFileInDir(t *testing.T) {
+	t.Run("creates temporary file with given content in directory", func(t *testing.T) {
+		content := "hello world"
+		dname, err := os.MkdirTemp("", "sampledir")
+		if err != nil {
+			t.Fatalf("failed to create dir: %v", err)
+		}
+
+		path := CreateTempFileInDir(t, content, dname)
+		defer RemoveDir(t, dname)
+
+		// Check if the file exists
+		if _, err := os.Stat(path); os.IsNotExist(err) {
+			t.Fatalf("expected file to exist, but it does not: %v", err)
+		}
+
+		// Read the file content and verify it matches
+		readContent, err := os.ReadFile(path)
+		if err != nil {
+			t.Fatalf("failed to read temp file: %v", err)
+		}
+
+		if string(readContent) != content {
+			t.Errorf("expected file content to be '%s', got '%s'", content, string(readContent))
+		}
+	})
+}
+
+func TestAppendToFilex3(t *testing.T) {
+	t.Run("removes the dir at the given path", func(t *testing.T) {
+		content := "hello world"
+		new_content := "!"
+		expected := "hello world!!!"
+		path := CreateTempFile(t, content)
+		defer RemoveFile(t, path)
+
+		// Read the file content before modification and verify it matches
+		readContent, err := os.ReadFile(path)
+		if err != nil {
+			t.Fatalf("failed to read temp file: %v", err)
+		}
+
+		if string(readContent) != content {
+			t.Errorf("expected file content to be '%s', got '%s'", content, string(readContent))
+		}
+
+		AppendToFilex3(t, path, new_content)
+
+		// Read the file content after modification and verify it matches
+		readContent, err = os.ReadFile(path)
+		if err != nil {
+			t.Fatalf("failed to read temp file: %v", err)
+		}
+
+		if string(readContent) != expected {
+			t.Errorf("expected file content to be '%s', got '%s'", content, string(readContent))
+		}
+
+	})
+}
+
+func TestRemoveDir(t *testing.T) {
+	t.Run("removes the dir at the given path", func(t *testing.T) {
+		dname, err := os.MkdirTemp("", "sampledir")
+		if err != nil {
+			t.Fatalf("failed to create dir: %v", err)
+		}
+
+		// Ensure the dir exists before removing
+		if _, err := os.Stat(dname); os.IsNotExist(err) {
+			t.Fatalf("expected file to exist, but it does not: %v", err)
+		}
+
+		RemoveDir(t, dname)
+
+		// Ensure the dir does not exist after removing
+		if _, err := os.Stat(dname); !os.IsNotExist(err) {
+			t.Errorf("expected file to be removed, but it still exists")
+		}
+
+	})
+}
+
+func TestRemoveFile(t *testing.T) {
+	t.Run("removes the file at the given path", func(t *testing.T) {
+		content := "file to be deleted"
+		path := CreateTempFile(t, content)
+
+		// Ensure the file exists before removing
+		if _, err := os.Stat(path); os.IsNotExist(err) {
+			t.Fatalf("expected file to exist, but it does not: %v", err)
+		}
+
+		RemoveFile(t, path)
+
+		// Ensure the file does not exist after removing
+		if _, err := os.Stat(path); !os.IsNotExist(err) {
+			t.Errorf("expected file to be removed, but it still exists")
+		}
+	})
+}