all: add custom hostname support for provisoning

cmd/cli/hostname.go

@@ -0,0 +1,14 @@
+package cli
+
+import "regexp"
+
+// validHostname reports whether hostname is a valid hostname.
+// A valid hostname contains 3 -> 64 characters and conform to RFC1123.
+func validHostname(hostname string) bool {
+	hostnameLen := len(hostname)
+	if hostnameLen < 3 || hostnameLen > 64 {
+		return false
+	}
+	validHostnameRfc1123 := regexp.MustCompile(`^(([a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9\-]*[a-zA-Z0-9])\.)*([A-Za-z0-9]|[A-Za-z0-9][A-Za-z0-9\-]*[A-Za-z0-9])$`)
+	return validHostnameRfc1123.MatchString(hostname)
+}