Add Docker setup, add environment vars for each flag

cmd/frontend/main.go

@@ -9,6 +9,7 @@ import (
 	"net/http"
 	"os"
 	"os/signal"
+	"strconv"
 	"syscall"
 )
 
@@ -16,10 +17,10 @@ import (
 var templatesFS embed.FS
 
 func main() {
-	listen := flag.String("listen", ":8080", "HTTP listen address")
-	target := flag.String("target", "localhost:9091", "default gRPC endpoint (aggregator or collector)")
-	n := flag.Int("n", 25, "default number of table rows")
-	refresh := flag.Int("refresh", 30, "meta-refresh interval in seconds (0 = disabled)")
+	listen := flag.String("listen", envOr("FRONTEND_LISTEN", ":8080"), "HTTP listen address (env: FRONTEND_LISTEN)")
+	target := flag.String("target", envOr("FRONTEND_TARGET", "localhost:9091"), "default gRPC endpoint, aggregator or collector (env: FRONTEND_TARGET)")
+	n := flag.Int("n", envOrInt("FRONTEND_N", 25), "default number of table rows (env: FRONTEND_N)")
+	refresh := flag.Int("refresh", envOrInt("FRONTEND_REFRESH", 30), "meta-refresh interval in seconds, 0 to disable (env: FRONTEND_REFRESH)")
 	flag.Parse()
 
 	funcMap := template.FuncMap{"fmtCount": fmtCount}
@@ -51,3 +52,20 @@ func main() {
 	log.Printf("frontend: shutting down")
 	srv.Shutdown(context.Background())
 }
+
+func envOr(key, def string) string {
+	if v := os.Getenv(key); v != "" {
+		return v
+	}
+	return def
+}
+
+func envOrInt(key string, def int) int {
+	if v := os.Getenv(key); v != "" {
+		if n, err := strconv.Atoi(v); err == nil {
+			return n
+		}
+		log.Printf("frontend: invalid int for %s=%q, using default %d", key, v, def)
+	}
+	return def
+}