Document that update-policy external is synchronous

diff --git a/doc/arm/reference.rst b/doc/arm/reference.rst
index 712d284ed90fe7d4d2c60a96518f9d3f49d851d2..38396f03a5846180080810e0934a01bde97bca68 100644 (file)
--- a/doc/arm/reference.rst
+++ b/doc/arm/reference.rst
@@ -7552,6 +7552,8 @@ the zone's filename, unless :any:`inline-signing` is enabled.
 
        The daemon replies with a four-byte value in network byte order, containing either 0 or 1; 0 indicates that the specified update is not permitted, and 1 indicates that it is.
 
+       .. warning:: The external daemon must not delay communication. This policy is evaluated synchronously; any wait period negatively affects :iscman:`named` performance.
+
 .. _multiple_views:
 
 Multiple Views