dnsdist: Better documentation of newServer's 'sockets' parameter

Courtesy of Neil Cook (thanks!).

diff --git a/pdns/dnsdistdist/docs/advanced/tuning.rst b/pdns/dnsdistdist/docs/advanced/tuning.rst
index 8732fce6c21af43859321d51947b535edd8e0392..f6f03f4ee222c43f7eb7ce79c52c1aa130ffde28 100644 (file)
--- a/pdns/dnsdistdist/docs/advanced/tuning.rst
+++ b/pdns/dnsdistdist/docs/advanced/tuning.rst
@@ -54,7 +54,7 @@ Large installations running dnsdist before 1.4.0 are advised to increase the def
 Looking at ``udp-in-errors`` in :func:`dumpStats` will reveal whether the system is dropping UDP datagrams because dnsdist does not pick them up fast enough. In that case it might be good to add more :func:`addLocal` directives.
 In the same way, if the number of ``Drops`` in :func:`showServers` increase fast enough, it might mean that the backend is overloaded but also that the UDP received thread is. In that case adding more :func:`newServer`
 
-Using a single connected UDP socket to contact a backend, and thus a single (source address, source port, destination address, destination port) tuple, might not play well with some load-balancing mechanisms present in front of the backend. Linux's ``reuseport``, for example, does not balance the incoming datagrams to several threads in that case. That can be worked around by using the ``sockets`` option of the :func:`newServer` directive to open several sockets instead of one. dnsdist will then select a socket using round-robin to forward a query to the backend, and use event multiplexing on the receiving side.
+Using a single connected UDP socket to contact a backend, and thus a single (source address, source port, destination address, destination port) tuple, might not play well with some load-balancing mechanisms present in front of the backend. Linux's ``reuseport``, for example, does not balance the incoming datagrams to several threads in that case. That can be worked around by using the ``sockets`` option of the :func:`newServer` directive to open several sockets instead of one. You may want to set that number to a value somewhat higher than the number of worker threads configured in the backend. dnsdist will then select a socket using round-robin to forward a query to the backend, and use event multiplexing on the receiving side.
 
 .. figure:: ../imgs/DNSDistDoH.png
    :align: center

diff --git a/pdns/dnsdistdist/docs/reference/config.rst b/pdns/dnsdistdist/docs/reference/config.rst
index cbd8a06370e67e63572d838fbd1a827fb29ef0e3..10cb5f9827999ea67d6f9d44107735d3cbf90ae0 100644 (file)
--- a/pdns/dnsdistdist/docs/reference/config.rst
+++ b/pdns/dnsdistdist/docs/reference/config.rst
@@ -527,7 +527,7 @@ Servers
                              --   "address@interface", e.g. "192.0.2.2@eth0"
       addXPF=NUM,            -- Add the client's IP address and port to the query, along with the original destination address and port,
                              -- using the experimental XPF record from `draft-bellis-dnsop-xpf <https://datatracker.ietf.org/doc/draft-bellis-dnsop-xpf/>`_ and the specified option code. Default is disabled (0)
-      sockets=NUM,           -- Number of sockets (and thus source ports) used toward the backend server, defaults to a single one
+      sockets=NUM,           -- Number of sockets (and thus source ports) used toward the backend server, defaults to a single one. Note that for backends which are multithreaded, this setting will have an effect on the number of cores that will be used to process traffic from dnsdist. For example you may want to set 'sockets' to a number somewhat higher than the number of worker threads configured in the backend, particularly if the Linux kernel is being used to distribute traffic to multiple threads listening on the same socket (via `reuseport`).
       disableZeroScope=BOOL, -- Disable the EDNS Client Subnet 'zero scope' feature, which does a cache lookup for an answer valid for all subnets (ECS scope of 0) before adding ECS information to the query and doing the regular lookup. This requires the ``parseECS`` option of the corresponding cache to be set to true
       rise=NUM,              -- Require NUM consecutive successful checks before declaring the backend up, default: 1
       useProxyProtocol=BOOL, -- Add a proxy protocol header to the query, passing along the client's IP address and port along with the original destination address and port. Default is disabled.