Output warning log if cluster ID has invalid characters

Signed-off-by: Frances Thai <[email protected]>

go/vt/vtadmin/cluster/config.go

@@ -22,6 +22,7 @@ import (
 	stderrors "errors"
 	"fmt"
 	"io"
+	"regexp"
 	"strconv"
 	"time"
 
@@ -50,6 +51,8 @@ var (
 	DefaultReadPoolWaitTimeout = time.Millisecond * 100
 )
 
+var ClusterIDPattern = regexp.MustCompile("^[a-zA-Z0-9+.-]*$")
+
 // Config represents the options to configure a vtadmin cluster.
 type Config struct {
 	ID                   string
@@ -149,6 +152,10 @@ func LoadConfig(r io.Reader, configType string) (cfg *Config, id string, err err
 		return nil, "", ErrNoConfigID
 	}
 
+	if !ClusterIDPattern.MatchString(id) {
+		log.Warning("cluster id must only contain alphanumeric characters, +, ., or -")
+	}
+
 	tmp := map[string]string{}
 	if err := v.Unmarshal(&tmp); err != nil {
 		return nil, id, err