Warn if configuration file not found, fail if missing auths or modules

Fixes #1456

Signed-off-by: Brian Candler <[email protected]>

Author: candlerb

config/config.go

@@ -16,6 +16,7 @@ package config
 import (
 	"errors"
 	"fmt"
+	"log/slog"
 	"os"
 	"path/filepath"
 	"regexp"
@@ -25,13 +26,16 @@ import (
 	"gopkg.in/yaml.v2"
 )
 
-func LoadFile(paths []string, expandEnvVars bool) (*Config, error) {
+func LoadFile(logger *slog.Logger, paths []string, expandEnvVars bool) (*Config, error) {
 	cfg := &Config{}
 	for _, p := range paths {
 		files, err := filepath.Glob(p)
 		if err != nil {
 			return nil, err
 		}
+		if len(files) == 0 && logger != nil {
+			logger.Warn("No file found matching pattern", "file", p)
+		}
 		for _, f := range files {
 			content, err := os.ReadFile(f)
 			if err != nil {

config_test.go

@@ -22,7 +22,7 @@ import (
 
 func TestHideConfigSecrets(t *testing.T) {
 	sc := &SafeConfig{}
-	err := sc.ReloadConfig([]string{"testdata/snmp-auth.yml"}, false)
+	err := sc.ReloadConfig(nil, []string{"testdata/snmp-auth.yml"}, false)
 	if err != nil {
 		t.Errorf("Error loading config %v: %v", "testdata/snmp-auth.yml", err)
 	}
@@ -41,7 +41,7 @@ func TestHideConfigSecrets(t *testing.T) {
 
 func TestLoadConfigWithOverrides(t *testing.T) {
 	sc := &SafeConfig{}
-	err := sc.ReloadConfig([]string{"testdata/snmp-with-overrides.yml"}, false)
+	err := sc.ReloadConfig(nil, []string{"testdata/snmp-with-overrides.yml"}, false)
 	if err != nil {
 		t.Errorf("Error loading config %v: %v", "testdata/snmp-with-overrides.yml", err)
 	}
@@ -56,7 +56,7 @@ func TestLoadConfigWithOverrides(t *testing.T) {
 func TestLoadMultipleConfigs(t *testing.T) {
 	sc := &SafeConfig{}
 	configs := []string{"testdata/snmp-auth.yml", "testdata/snmp-with-overrides.yml"}
-	err := sc.ReloadConfig(configs, false)
+	err := sc.ReloadConfig(nil, configs, false)
 	if err != nil {
 		t.Errorf("Error loading configs %v: %v", configs, err)
 	}
@@ -75,7 +75,7 @@ func TestEnvSecrets(t *testing.T) {
 	t.Setenv("ENV_PRIV_PASSWORD", "snmp_priv_password")
 
 	sc := &SafeConfig{}
-	err := sc.ReloadConfig([]string{"testdata/snmp-auth-envvars.yml"}, true)
+	err := sc.ReloadConfig(nil, []string{"testdata/snmp-auth-envvars.yml"}, true)
 	if err != nil {
 		t.Errorf("Error loading config %v: %v", "testdata/snmp-auth-envvars.yml", err)
 	}
@@ -106,7 +106,7 @@ func TestEnvSecretsMissing(t *testing.T) {
 	t.Setenv("ENV_PRIV_PASSWORD", "snmp_priv_password")
 
 	sc := &SafeConfig{}
-	err := sc.ReloadConfig([]string{"testdata/snmp-auth-envvars.yml"}, true)
+	err := sc.ReloadConfig(nil, []string{"testdata/snmp-auth-envvars.yml"}, true)
 	if err != nil {
 		// we check the error message pattern to determine the error
 		if strings.Contains(err.Error(), "environment variable not found") {
@@ -120,7 +120,7 @@ func TestEnvSecretsMissing(t *testing.T) {
 // When SNMPv2 was specified without credentials
 func TestEnvSecretsNotSpecified(t *testing.T) {
 	sc := &SafeConfig{}
-	err := sc.ReloadConfig([]string{"testdata/snmp-auth-v2nocreds.yml"}, true)
+	err := sc.ReloadConfig(nil, []string{"testdata/snmp-auth-v2nocreds.yml"}, true)
 	if err != nil {
 		t.Errorf("Error loading config %v: %v", "testdata/snmp-auth-v2nocreds.yml", err)
 	}

main.go

@@ -182,8 +182,8 @@ type SafeConfig struct {
 	C *config.Config
 }
 
-func (sc *SafeConfig) ReloadConfig(configFile []string, expandEnvVars bool) (err error) {
-	conf, err := config.LoadFile(configFile, expandEnvVars)
+func (sc *SafeConfig) ReloadConfig(logger *slog.Logger, configFile []string, expandEnvVars bool) (err error) {
+	conf, err := config.LoadFile(logger, configFile, expandEnvVars)
 	if err != nil {
 		return err
 	}
@@ -214,10 +214,20 @@ func main() {
 	prometheus.MustRegister(versioncollector.NewCollector("snmp_exporter"))
 
 	// Bail early if the config is bad.
-	err := sc.ReloadConfig(*configFile, *expandEnvVars)
+	err := sc.ReloadConfig(logger, *configFile, *expandEnvVars)
 	if err != nil {
 		logger.Error("Error parsing config file", "err", err)
-		logger.Error("Possible version missmatch between generator and snmp_exporter. Make sure generator and snmp_exporter are the same version.")
+		logger.Error("Possible version mismatch between generator and snmp_exporter. Make sure generator and snmp_exporter are the same version.")
+		logger.Error("See also: https://github.com/prometheus/snmp_exporter/blob/main/auth-split-migration.md")
+		os.Exit(1)
+	}
+	if len(sc.C.Modules) == 0 {
+		logger.Error("Configuration is missing Modules. Did you provide any configuration file?")
+		os.Exit(1)
+	}
+	if len(sc.C.Auths) == 0 {
+		logger.Error("Configuration is missing Auths.")
+		logger.Error("Possible version mismatch between generator and snmp_exporter. Make sure generator and snmp_exporter are the same version.")
 		logger.Error("See also: https://github.com/prometheus/snmp_exporter/blob/main/auth-split-migration.md")
 		os.Exit(1)
 	}
@@ -235,13 +245,13 @@ func main() {
 		for {
 			select {
 			case <-hup:
-				if err := sc.ReloadConfig(*configFile, *expandEnvVars); err != nil {
+				if err := sc.ReloadConfig(logger, *configFile, *expandEnvVars); err != nil {
 					logger.Error("Error reloading config", "err", err)
 				} else {
 					logger.Info("Loaded config file")
 				}
 			case rc := <-reloadCh:
-				if err := sc.ReloadConfig(*configFile, *expandEnvVars); err != nil {
+				if err := sc.ReloadConfig(logger, *configFile, *expandEnvVars); err != nil {
 					logger.Error("Error reloading config", "err", err)
 					rc <- err
 				} else {