pdns/dnsdistdist/docs/guides/downstreams.rst

   1 Configuring Downstream Servers
   2 ==============================
   3
   4 As dnsdist is a loadbalancer and does not do any DNS resolving or serving by itself, it needs downstream servers.
   5 To add downstream servers, either include them on the command line::
   6
   7     dnsdist -l 130.161.252.29 -a 130.161.0.0/16 8.8.8.8 208.67.222.222 2620:0:ccc::2 2620:0:ccd::2
   8
   9 Or add them to the configuration file:
  10
  11 .. code-block:: lua
  12
  13     setLocal("130.161.252.29:53")
  14     setACL("130.161.0.0/16")
  15     newServer("8.8.8.8")
  16     newServer("208.67.222.222")
  17     newServer("2620:0:ccc::2")
  18     newServer("2620:0:0ccd::2")
  19
  20 These two equivalent configurations give you sane load balancing using a very sensible distribution policy.
  21 Many users will simply be done with this configuration.
  22 It works as well for authoritative as for recursive servers.
  23
  24 Healthcheck
  25 -----------
  26 dnsdist uses a health check, sent once every second, to determine the availability of a backend server.
  27
  28 By default, an A query for "a.root-servers.net." is sent.
  29 A different query type and target can be specified by passing, respectively, the ``checkType`` and ``checkName`` parameters to :func:`newServer`.
  30
  31 The default behavior is to consider any valid response with an RCODE different from ServFail as valid.
  32 If the ``mustResolve`` parameter of :func:`newServer` is set to ``true``, a response will only be considered valid if its RCODE differs from NXDomain, ServFail and Refused.
  33
  34 The number of health check failures before a server is considered down is configurable via the ``maxCheckFailures`` parameter, defaulting to 1.
  35 The CD flag can be set on the query by setting ``setCD`` to true.
  36 e.g.::
  37
  38   newServer({address="192.0.2.1", checkType="AAAA", checkName="a.root-servers.net.", mustResolve=true})
  39
  40 Source address selection
  41 ------------------------
  42
  43 In multi-homed setups, it can be useful to be able to select the source address or the outgoing
  44 interface used by dnsdist to contact a downstream server. This can be done by using the `source` parameter::
  45
  46   newServer({address="192.0.2.1", source="192.0.2.127"})
  47   newServer({address="192.0.2.1", source="eth1"})
  48   newServer({address="192.0.2.1", source="192.0.2.127@eth1"})
  49
  50 The supported values for source are:
  51 - an IPv4 or IPv6 address, which must exist on the system
  52 - an interface name
  53 - an IPv4 or IPv6 address followed by '@' then an interface name
  54
  55 Please note that specifying the interface name is only supported on system having `IP_PKTINFO`.