feat: Use env vars to set config file

* Set DB pointer for CEEMS LB only when exists

Signed-off-by: Mahendra Paipuri <mahendra.paipuri@gmail.com>

pkg/api/cli/cli.go

@@ -113,11 +113,11 @@ func (b *CEEMSServer) Main() error {
 		webConfigFile = b.App.Flag(
 			"web.config.file",
 			"Path to configuration file that can enable TLS or authentication. See: https://github.com/prometheus/exporter-toolkit/blob/master/docs/web-configuration.md",
-		).Default("").String()
+		).Envar("CEEMS_API_SERVER_WEB_CONFIG_FILE").Default("").String()
 		configFile = b.App.Flag(
 			"config.file",
 			"Path to CEEMS API server configuration file.",
-		).Default("").String()
+		).Envar("CEEMS_API_SERVER_CONFIG_FILE").Default("").String()
 
 		// Testing related hidden CLI args
 		skipDeleteOldUnits = b.App.Flag(

pkg/lb/cli/cli.go

@@ -138,11 +138,11 @@ func (lb *CEEMSLoadBalancer) Main() error {
 		webConfigFile = lb.App.Flag(
 			"web.config.file",
 			"Path to configuration file that can enable TLS or authentication. See: https://github.com/prometheus/exporter-toolkit/blob/master/docs/web-configuration.md",
-		).Default("").String()
+		).Envar("CEEMS_LB_WEB_CONFIG_FILE").Default("").String()
 		configFile = lb.App.Flag(
 			"config.file",
 			"Configuration file path.",
-		).Default("").String()
+		).Envar("CEEMS_LB_CONFIG_FILE").Default("").String()
 		maxProcs = lb.App.Flag(
 			"runtime.gomaxprocs", "The target number of CPUs Go will run on (GOMAXPROCS)",
 		).Envar("GOMAXPROCS").Default("1").Int()

pkg/lb/frontend/frontend.go

@@ -10,6 +10,7 @@ import (
 	"io"
 	"net/http"
 	"net/url"
+	"os"
 	"path/filepath"
 	"slices"
 	"strings"
@@ -84,8 +85,12 @@ func NewLoadBalancer(c *Config) (LoadBalancer, error) {
 			return nil, err
 		}
 
-		if db, err = sql.Open("sqlite3", dbAbsPath); err != nil {
-			return nil, err
+		// Set DB pointer only if file exists. Else sql.Open will create an empty
+		// file as if exists already
+		if _, err := os.Stat(dbAbsPath); err == nil {
+			if db, err = sql.Open("sqlite3", dbAbsPath); err != nil {
+				return nil, err
+			}
 		}
 	}