docs: describe resource-limits metric

information taken from @rgacogne 's email:
https://mailman.powerdns.com/pipermail/pdns-users/2021-October/027446.html

diff --git a/pdns/recursordist/docs/metrics.rst b/pdns/recursordist/docs/metrics.rst
index 1cf9492ace8e29ab33d03dd4309dd90114b9bd7c..340d580d8f2bdc481ebbeb18998ea8793426f21a 100644 (file)
--- a/pdns/recursordist/docs/metrics.rst
+++ b/pdns/recursordist/docs/metrics.rst
@@ -487,6 +487,8 @@ failed-host-entries
 ^^^^^^^^^^^^^^^^^^^
 number of servers that failed to resolve
 
+.. _stat-fd-usage:
+
 fd-usage
 ^^^^^^^^
 Number of currently used file descriptors.
@@ -661,7 +663,10 @@ number of contended record cache lock acquisitions
 
 resource-limits
 ^^^^^^^^^^^^^^^
-counts number of queries that could not be   performed because of resource limits
+Counts the number of queries that could not be performed because of resource limits. 
+This counter is increased when Recursor encounters a network issue that does not seem to be caused by the remote end. 
+For example when it runs out of file descriptors (monitor :ref:`stat-fd-usage`) or when there is no route to a
+given IP address.
 
 security-status
 ^^^^^^^^^^^^^^^