=head1 NAME

gdnsd-plugin-geoip - gdnsd meta-plugin for GSLB + failover via MaxMind's
GeoIP databases

=head1 SYNOPSIS

Minimal example gdnsd config file using this plugin:

  plugins => { geoip => {
    maps => {
      my_prod_map => {
        geoip2_db => GeoIP2-City.mmdb,
        datacenters => [dc-03, dc-02, dc-01, dc-fail],
        map => {
            EU => {
                DE => [dc-03, dc-01, dc-fail],
                CH => [dc-01, dc-03, dc-fail]
            },
            NA => { MX => [dc-02, dc-fail] }
        }
      },
      my_auto_map => {
        geoip_db => GeoIPCityv6.dat,
        datacenters => [dc1, dc2],
        auto_dc_coords => {
           dc1 => [ 38.9, -77 ],
           dc2 => [ 50.1, 8.7 ],
        }
      }
    },
    resources => {
      prod_www => {
        map => my_prod_map
        service_types => up
        dcmap => {
          dc-01 => 192.0.2.1,
          dc-02 => { lb01 => 192.0.2.2, lb02 => 192.0.2.3 },
          dc-03 => [ 192.0.2.4, 192.0.2.5, 192.0.2.6 ],
          dc-fail => last.resort.cname.example.net.
        }
      }
      corp_www => {
        map => my_auto_map
        dcmap => {
          dc1 => 192.0.2.100,
          dc2 => 192.0.2.101
        }
      }
    }
  }}

Example zonefile RRs:

  www      600 DYNA geoip!prod_www
  www-dc01 600 DYNA geoip!prod_www/dc-01
  www.corp 600 DYNA geoip!corp_www

=head1 DESCRIPTION

B<gdnsd-plugin-geoip> uses MaxMind's GeoIP binary databases to
map address and CNAME results based on geography and
monitored service availability.  It fully supports both
IPv6 and the emerging edns-client-subnet standard.  If a request
contains the edns-client-subnet option with a source netmask greater
than zero, the edns-client-subnet information will be used instead
of the source IP of the request (the IP of the querying cache).

It supports both the legacy GeoIP1 format databases which typically
end in F<.dat> and the newer GeoIP2 format database which typically end in
F<.mmdb>.  There are a few differences in the plugin's behavior depending on
the database type in use, which are noted throughout this document.  It is
notable that what was called the singular "Region" in GeoIP1 is now multiple
"Subdivisions" in GeoIP2.  Both occupy the hierarchical space between
"Country" and "City" level information.  In the GeoIP2 case there can be
several layers of Subdivisions, which depend entirely on how a Country is
broken down in ISO3166-2.  Assume the terms Region and Subdivision are
interchangeable for the most part throughout this document.

It can also be used with no GeoIP database at all, in which case the only
network-mapping input comes from the C<nets> config data or an external
C<nets> file, which explicitly map subnets to datacenter lists.

This plugin can operate in an automatic distance-based mode (using
City-level coordinate information rather than an external file and a
Region-level db).  It can also operate coordinate-free and rely on the
user to configure a hierarchical map of cascading default
user-location-to-datacenter mappings, starting at the continent level.

The two modes can also be effectively mixed at geographic boundaries.

For each C<map> you define (which maps geographic location codes to
preference-ordered lists of your datacenter locations), this plugin merges
all of the raw GeoIP subnets into the largest possible supernets which
contain identical responses in your configuration.  These in turn are used
to set larger edns-client-subnet scope masks than you'd see simply
returning raw GeoIP results.

=head1 PLUGIN_METAFO

The documentation for L<gdnsd-plugin-metafo(8)> is required reading for
understanding the geoip plugin documentation here.  The geoip plugin is an
exact superset of the metafo plugin, and re-uses almost all of the metafo
plugin's source code.  Metafo does failover along a single, global, ordered
list of datacenters.  What plugin_geoip adds on top of the functionality
of metafo is the ability to have the order of the datacenter failover list
become dynamic per-request based on geographic hints derived from the
client's network address.

=head1 FILE LOCATIONS

The configuration of this plugin can reference several external
configuration and/or data files.  By default, all files referenced in
this plugin's configuration are loaded from the F<geoip> subdirectory
of the daemon's configuration directory (default F<@GDNSD_DEFPATH_CONFIG@>).
You can load from other locations by specifying absolute file paths.

=head1 CONFIGURATION - TOP-LEVEL

The top level of the geoip plugin's configuration (i.e. C<plugins =E<gt> {
geoip =E<gt> { ... } }>) supports only two special keys, both of which are
required and expanded upon in detail in the next two sections: C<maps>, and
C<resources>.  The C<maps> section defines one or more named mappings of
location information from GeoIP binary databases to ordered subsets of
datacenter names.  The C<resources> section defines one or more named
resources, each of which references one of the named maps and resolves
datacenter names to specific sets of addresses or CNAMEs.

Any other keys present at this level will be inherited down inside of each
per-resource hash inside the C<resources> stanza, acting as per-resource
defaults for anything not defined explicitly there.

=head1 CONFIGURATION - MAPS

The C<maps> stanza supports one special configuration key at the top level:

=head2 C<city_region_names = region_codes.csv>

String, filename, optional.  GeoIP1 City databases use FIPS 10-4 codes for
the names of Regions outside of the US and Canada, and two-letter national
alpha codes within the US and Canada.  For example the Geneve region of
Switzerland is identified as C<07> in the database.  By default you would
have to use these relatively confusing region codes in your hierarchical
maps that make use of Region-level information (e.g. C<EU =E<gt> { CH
=E<gt> { 07 =E<gt> { Geneva =E<gt> [ ... ] } } } }>.  If this option is
specified, it points to a text file that maps these FIPS codes to
canonical, memorable full names for clearer map configuration (e.g. C<EU
=E<gt> { CH =E<gt> { Geneve =E<gt> { Geneva =E<gt> [ ... ] } } } }>.  Note
that while older versions of this data did not map the US/Canadian
two-letter alpha codes, newer versions do (e.g. TX -> Texas).

This setting does not affect the GeoIP C<Region> -format databases, which
have no region codes outside of the US and Canada, and always need the
two-letter alpha codes in the map.

It also does not affect GeoIP2 databases, as they all use ISO3166-2 codes
for subdivision (aka region) data directly, which are at least usually more
intuitive than FIPS.

The file format is a simple subset of the CSV format with 3 fields: ISO
3166-1 country code, FIPS 10-4 region code (or two-letter alpha in
US/Canada), and the region name in double-quotes.  It is recommended you
download this file directly from MaxMind's reference copy in this format.
As of this writing, it is available from them at the following URL:
L<http://www.maxmind.com/download/geoip/misc/region_codes.csv>.

=head1 CONFIGURATION - PER-MAP

All other C<maps>-level configuration keys are the names of the maps you
choose to define.  A map, conceptually, is a mapping between geography
and/or network topology to varying ordered datacenter sub-sets.  The value
of each named map must be a hash, and the following configuration keys
apply within:

=head2 C<geoip2_db = GeoIP2-City.mmdb>

String, filename, optional.  This is the filename of a MaxMind GeoIP2 format
database.  It should contain either the City or Country data model.  There is
no distinction made here for the IP version, and it is normal for these
databases to contain both IPv4 and IPv6 data together.  If one or the other is
missing, clients using that address family will be defaulted.  If this
parameter is set, then the legacy C<geoip_db> and C<geoip_db_v4_overlay> are
not allowed alongside it.

=head2 C<geoip_db = GeoIPv6.dat>

String, filename, optional.  This is the filename of one of the supported
MaxMind GeoIP1 database types.  It will be reloaded at runtime (without any
significant query interruptions) if a change to the database file is
detected.

=head2 C<geoip_db_v4_overlay = GeoIP.dat>

String, pathname, optional.  This specifies an optional IPv4-level GeoIP1
database to overwrite the IPv4 sub-space of the IPv6 data loaded from
C<geoip_db>.  It must be a V4-format database, and C<geoip_db> must be
defined as a V6-format database.  In all other respects, it is similar to
C<geoip_db>.

As of this writing, MaxMind doesn't sell a commercial GeoIP1v6 database.
What they offer are free IPv6 GeoLite1 database downloads, which include the
IPv4 subset in the less-accurate GeoLite1 form.  This option allows you to
use these GeoLite1v6 databases for IPv6 coverage, and then overlay your paid
commercial GeoIP1v4 data on top for more accurate IPv4 results.

=head2 C<datacenters = [ one, two, three, ... ]>

Array of strings, required.  This is the total set of datacenter names used
by this map.  You must define at least one datacenter name (although 2 or
more would be infinitely more useful).  At this time, there is a maximum
limit of 254 datacenter names per map, although this could be raised if
anyone requires it.  The order specified here is the fallback default
result ordering in various default cases (e.g. if no explicit top-level map
default list is given).

=head2 C<city_no_region = true>

Boolean, default C<false>.  If this key is set to C<true> and the database
is a City-level database, the Region/Subdivision-level information within it
will be completely ignored for mapping purposes.  Your hierarchical map
structure will now be C<continent =E<gt> country =E<gt> city> rather than
C<continent =E<gt> country =E<gt> region/subdivision =E<gt> city>.

=head2 C<nets = { ... }>

Key-value hash, optional (see below for alternate form).  If specified, the
contents should be key-value pairs of C<network/netmask> mapped to a
datacenter name (or an array of datacenter names).  Any
network-to-datacenter mappings specified here will override mappings
determined via GeoIP.  Note that it is illegal to specify networks in the
IPv4-like subspaces of IPv6 other than v4compat, but it is legal to specify
actual IPv4 networks (which are treated identically to v4compat).  See the
section on IPv4 Compatible Addresses later in this document for more
details.  The order of the networks is unimportant; they will always be
sorted and inserted such that an entry which is a subnet of another entry
is not obliterated by the parent supernet.

    nets => {
        10.0.0.0/8 => [ dc1, dc2 ],
        192.0.2.128/25 => dc3
        2001:DB8::/32 => [ dc4, dc5, dc6 ],
    }

In the case that one entry is a subnet of another with a different result
dclist, the entries are merged correctly such that the supernet surrounds
the subnet.  In the case of an exact duplicate entry (or an effective one,
after merging smaller subnets) with a different dclist, it is arbitrary
which one "wins" and the condition is warned about.  If you care about
this case, you should sanitize your nets data beforehand with an external
tool and/or parse for the warning message in log outputs.

=head2 C<nets = nets_file_name>

String pathname, optional.  A variant of the above, but the contents of the
key-value hash are loaded from the named external file.  This makes life
easier for external tools and scripts generating large sets of nets entries
(e.g. from BGP data).  The file will be monitored for changes and reloaded
at runtime much like the GeoIP databases.

=head2 C<map = { ... }>

Key-value hash, optional.  This is the heart of a named map which uses
GeoIP: the map itself, which maps places to ordered lists of datacenters.
It requires that C<geoip_db> or C<geoip2_db> is also specified, and makes no
sense without it.

This is a nested key-value hash.  At each level, the keys are location
codes (continent, country, region/subdivision, or city information depending
on depth), and the values are either an ordered datacenter array (e.g. C<[
dc03, dc01, dc04 ]>), or a sub-hash containing a deeper level of distinction.
At each layer, a special key named C<default> is available, which sets the
default for everything within the current scope.  The top-level default itself
defaults to the ordered list from C<datacenters> in the normal case.  If
the entire C<map> stanza is missing or empty, you just get the default
behavior of C<default>.  A datacenter array can also be empty, which
implies that this location is mapped to receive no response data (the
server will still respond to the query, and will not issue an NXDOMAIN.  It
will simply be a NODATA/NOERROR response like you'd get if there were no
records of this type, but could be records of other types for the same
name).

The map has slightly different interpretations for GeoIP2 vs GeoIP1 databases:

=over 4

=item GeoIP1

The meaningful location keys at the top level are continent codes, of which
there are primarily seven in MaxMind's databases: C<AF> for Africa, C<AS>
for Asia, C<NA> for North America, C<SA> for South America, C<EU> for
Europe, C<OC> for Oceania, and C<AN> for Antarctica.  There is also an
eighth continent-level code which is, literally, C<-->.  This is a sort of
fallback "no information available" continent code, and it contains the
special country codes C<A1>, C<A2>, C<O1>, and C<-->, which represent
Anonymous Proxies, Satellite Providers, Other, and Unknown, respsectively.

The next layer (the sub-hash beneath any continent code) maps ISO-3166-1
2-letter country codes, which as with continents can map directly to
datacenters, or to yet another recursive layer.

The next two layers deep are for Region and City level information, only
available from the Region and City type databases.  The Region database
type only provides region information for the US and Canada, using the
standard local 2-letter abbrevations (e.g. AB for Alberta, OK for
Oklahama).  The City databases use those same region abbrevations for the
US and Canada, but use either FIPS 10-4 2-letter codes or full region names
for the rest of the world's regions (as detailed earlier in, and controlled
by, the C<city_region_names> option).

The actual City names at the final layer appear to be encoded using some
form of ISO8859-1 and/or CP1252 character set in the databases themselves,
and your map entries will have to match byte-for-byte in the case of
non-ASCII characters.  May come up with a better solution for this down the
road.

=item GeoIP2

As with GeoIP1, the top level of the hierarchy is comprised of MaxMind's seven
continent codes: C<AF> for Africa, C<AS> for Asia, C<NA> for North America,
C<SA> for South America, C<EU> for Europe, C<OC> for Oceania, and C<AN> for
Antarctica.  There is no special C<--> continent for various types of
unknowns; those database entries that lack some or all information at this
level simply take the appropriate defaults for the level of detail they
possess.

The next level, again as in GeoIP1, is the ISO 3166-1 2-letter country code.

From here GeoIP2 has a number of Subdivision levels, the count of which varies
for different network database entries.  In the US, for example, there is only
one level of subdivision data for the US States.  In the Czech
Republic there are two levels of subdivision: first into 14 regions, and then
further into 91 districts.  Subdivisions are all specified using their
ISO 3166-2 codes directly.

After all subdivision levels, the final level is the City level.  The City
names are all in the UTF-8 character set.  Currently this plugin only uses the
English city names from the database, even though other languages may be
available depending on the database.

As a pragmatic answer to the issues that can arise with multiple subdivision
layers, in the GeoIP2 case the map automatically searches deeper in the
database data when no map match is found at a given level of the map hierarchy
beneath the Country level.  This means you can skip over any levels of
Subdivision detail in your map that are irrelevant to you.  This mostly
supplants the practical need for the C<city_no_region> and C<skip_level>
functionality that was used with GeoIP1 maps, but those features remain
functional as well.

For example, this targets the New Zealand regional council subdivision of
Otago without explicitly specifying the enclosing subdivision for the South
Island:

  { OC => { NZ => { OTA => [...] } } }

As another example, this works correctly for targeting the city of Paris
without caring about what layers of subdivisions lie between it and FR:

  { EU => { FR => { Paris => [...] } } }

=back

There is also one other special key (aside from C<default>) available at
all levels of the map hierarchy, a boolean named C<skip_level>, default
C<false>.  If set within the hierarchical C<map> at any layer, it causes
the next layer of detail to be skipped for this portion of the map.  For
example, setting this at the very top layer would mean that the top layer
would contain country-level codes directly, without an enclosing
continent-level hierarchy.  Setting it within a country would mean that
city names are used directly within that country, without an intervening
layer of region names.  This option is not aware of the C<city_no_region>
option, so e.g. setting that option and specifying C<skip_level> at the
country-level would result in no further information being available within
that country (as C<skip_level> would skip the remaining layer of city data).

=head1 CONFIGURATION - MAPS - CITY AUTO MODE

"City-auto-mode" is a special mode of operation that automatically maps out
the world to your datacenters based on coordinate math, so that you don't
have to manually construct a complex hierarchical C<map>.  It can still be
mixed with C<map> of course, allowing you to use auto-mode for only select
geographic areas if you wish (or disabling it for select areas by
specifying manual lists).  The key parameter is C<auto_dc_coords>, which
enables city-auto-mode.

=over 4

=item C<auto_dc_coords = { ... }>

Key-value hash, optional.  If this option is specified, the whole map's
basic mode of operation changes to "city-auto-mode".  The contents of the
hash are a key for each datacenter named in C<datacenters>, with their
values set to an array of C<[lat, lon]> in decimal degree units.  When
city-auto-mode is enabled by this, the following configuration-validation
changes occur from the default, static-mapping mode: the loaded GeoIP
database(s) are required be City-level databases, and the special keyword
C<auto> becomes a legal "datacenter list" in the C<map> stanza.

With city-auto-mode enabled, the top-level map C<default> defaults to
C<auto>, but can be overridden with a manual list.  For any location that
maps to C<auto>, the coordinates specified here in C<auto_dc_coords> will
be compared with the coordinates from the City-level database(s) to
determine an automatic distance-sorted datacenter list.

If you omit one or more defined datacenters from the coordinate list in
C<auto_dc_coords>, those datacenters will not be used in automatic results,
but will still be available for manual use via C<map> and/or C<nets>
entries.

=item C<auto_dc_limit = N>

Unsigned integer, optional, default 3.  When city-auto-mode is in effect,
this is the upper length limit for auto-generated lists.  3 is a reasonable
default even if you have a considerably longer set of datacenters, as this
provides a primary as well as two fallbacks.  Raising this to a large
number in the presence of a long datacenter list will cause the set of
unique result datacenter lists to increase rapidly, and thus reduce the
optimization of the final result database for edns-client-subnet purposes.
It's really not worth raising this value in almost any case, unless you
really need to handle more than 3 random datacenters going offline at the
same time and still have clients fail elsewhere.  The value zero is treated
as unlimited (highly un-recommended).

=back

Under city-auto-mode, when the top-level default is (explicitly or
implicitly) C<auto>, there is still a fallback static ordering which is the
whole ordered C<datacenters> list, which is the normal static default
C<default> when not in city-auto-mode.  This fallback is used when no
location information is available at all (e.g. IPv6 client vs IPv4 GeoIP
DB, Anonymous Proxies, etc).

=head1 MAP TESTING

A binary program C<gdnsd_geoip_test> is included.  This can be used
directly from the commandline, parses the relevant bits of your gdnsd
config file for geoip map info, and then provides datacenter list results
for IP address + map combinations supplied by the user.  Useful for
debugging your maps and testing the mapping of client IPs.  It has a
separate manpage L<gdnsd_geoip_test(1)>.

=head1 CONFIGURATION - RESOURCES

Resource-level configuration within the C<resources> stanza is nearly
identical to the resources configuration of the metafo plugin, with all of
the same basic behaviors about synthesizing or directly referencing the
configuration of other plugins per-datacenter.  The only real difference
is that metafo's per-resource C<datacenters> array is replaced with
C<map =E<gt> mapname>, which references one of the maps defined in the
C<maps> stanza, described in detail earlier.  The set of defined
datacenters in the C<dcmap> stanza must match the total set of datacenters
defined by the referenced map.

=head1 META-PLUGIN INTERACTION

Both of the meta-plugins (C<metafo> and C<geoip>) can reference their own
as well as each others' resources by direct reference within a C<dcmap>, so
long as a resource does not directly refer to itself.  This allows
plugin-layering configurations such as geoip -> metafo -> weighted, or
metafo -> geoip -> multifo, or even metafo -> metafo -> simplefo, etc.

Bear in mind that once you begin using inter-meta-plugin references, you
could create a reference loop.  gdnsd does not currently detect or prevent
such loops, and they will cause complete runtime failure when queried,
probably by running out of stack space during recursion.

Additionally, C<geoip> can synthesize configuration for C<metafo>
resources, but the reverse does not hold; C<metafo> cannot synthesize
configuration for C<geoip> resources.

=head1 IPv4 Compatible Addresses

This plugin knows of six different relatively-trivial ways to map IPv4
addresses into the IPv6 address space.  These are shown below in as much
detail matters to this plugin, with C<NNNN:NNNN> in place of the copied
IPv4 address bytes:

         ::0000:NNNN:NNNN/96   # RFC 4291 - v4compat (deprecated)
         ::ffff:NNNN:NNNN/96   # RFC 4291 - v4mapped
    ::ffff:0000:NNNN:NNNN/96   # RFC 2765 - SIIT (obsoleted)
       64:ff9b::NNNN:NNNN/96   # RFC 6052 - Well-Known Prefix
    2001:0000:X:NNNN:NNNN/32   # RFC 4380 - Teredo (IPv4 bits are flipped)
           2002:NNNN:NNNN::/16 # RFC 3056 - 6to4

    (in the Teredo case above, "X" represents some variable non-zero bytes
     that occupy the center 64 bits of the address).

All of this plugin's internal lookup databases are IPv6 databases, and any
IPv4-like information is always stored in the v4compat space within these
databases.  When doing runtime lookups all other v4-like addresses (raw
IPv4 addresses, v4mapped, SIIT, WKP, Teredo, and 6to4) are converted to the
canonical v4compat IPv6 representation before querying the internal
databases.  The other representations (v4mapped, SIIT, WKP, Teredo, 6to4) are
Undefined internally, and will never be referenced at lookup-time due to
the v4compat conversion mentioned earlier.

The C<nets> stanza is not allowed to specify entries in the four undefined
v4-like IPv6 spaces (those other than v4compat).  Specify those networks as
normal IPv4 networks or v4compat networks instead.  Legitimate IPv6 C<nets>
entries which happen to be a supernet of any v4-like spaces will *not*
unduly affect v4-like lookups.  There is no functional difference between
v4compat and native v4 forms in C<nets>, e.g. C<192.0.2.0/24> and
C<::C000:0200/120> are completely identical.

GeoIP databases that are natively IPv4-only get all of their data loaded
into the v4compat space only.  For IPv6 GeoIP databases, by default we load
the v4compat space directly (which is where MaxMind stores IPv4 data in
their IPv6 databases), but ignore the v4mapped/SIIT/Teredo/6to4 spaces
(some of which are empty in MaxMind's databases, and some of which simply
alias the v4compat space).  When using an IPv6 GeoIP database combined with
an IPv4 GeoIP overlay (geoip_db_v4_overlay config), the v4compat space of
the IPv6 database is also ignored on loading, and the direct IPv4 data from
the IPv4 databasee takes its place.

=head1 ANOTHER CONFIG EXAMPLE

A relatively-maximal example config, showing the interaction of valid
C<maps> and C<resources> sections:

  service_types => {
    xmpp_svc => { plugin => "tcp_connect", ... }
    www_svc => { plugin => "http_status", ... }
  }
  plugins => {
    geoip => {
      maps => {
        city_region_names => fips_include,
        my_prod_map => {
          geoip_db => GeoIPCityv6.dat,
          geoip_db_v4_overlay => GeoIPCity.dat,
          city_no_region => false, # default
          datacenters => [us-01, de-01, sg-01],
          map => {
              # Hierarchy is Continent -> Country -> Region -> City
              NA => {
                US => {
                  skip_level => 1, # skip past region level
                  Dallas => [sg-01],
                }
              }
              SA => [us-01, sg-01, de-01],
              EU => {
                default => [eu-01, us-01, sg-01],
                CH => {
                  Geneve => {
                    Geneva => [sg-01],
                  }
                }
              }
              AF => [eu-01, us-01, sg-01],
              AS => [sg-01, eu-01, us-01],
              OC => [sg-01, us-01, eu-01],
          }
          nets => {
              10.0.0.0/8 => [ eu-01 ],
              2001:DB8::/32 => [ us-01 ],
          }
        }
        my_auto_map => {
          geoip_db => GeoIPCityv6.dat,
          geoip_db_v4_overlay => GeoIPCity.dat,
          datacenters => [us-01, de-01, sg-01],
          auto_dc_coords => {
             us-01 => [ 38.9, -77 ],
             de-01 => [ 50.1, 8.7 ],
             sg-01 => [ 1.3, 103.9 ],
          }
        }
      }
      resources => {
        prod_app => {
          map => my_auto_map
          # these two are inherited multifo config keys
          #  for all of the dcmap below:
          service_types => [www_svc, xmpp_svc],
          up_thresh => 0.4,
          dcmap => {
            us-01 => {
              lb01 => 192.0.2.1,
              lb02 => 192.0.2.2,
              lb03 => 192.0.2.3,
              lb01.v6 => 2001:DB8::1,
              lb02.v6 => 2001:DB8::2,
              lb03.v6 => 2001:DB8::3,
            },
            sg-01 => {
              lb01 => 192.0.2.4,
              lb02 => 192.0.2.5,
              lb03 => 192.0.2.6,
              lb01.v6 => 2001:DB8::4,
              lb02.v6 => 2001:DB8::5,
              lb03.v6 => 2001:DB8::6,
            },
            de-01 => {
              lb01 => 192.0.2.7,
              lb02 => 192.0.2.8,
              lb03 => 192.0.2.9,
              lb01.v6 => 2001:DB8::7,
              lb02.v6 => 2001:DB8::8,
              lb03.v6 => 2001:DB8::9,
            },
          }
        },
        prod_cdn => {
          map => my_prod_map,
          dcmap => {
            us-01 => us-cdn-provider.example.com.
            sg-01 => asia-cdn-provider.example.com.
            de-01 => europe-cdn-provider.example.com.
          }
        }
      }
    }
  }

Example zonefile RRs:

  app     600 DYNA geoip!prod_app
  app.us  600 DYNA geoip!prod_app/us-01
  app.sg  600 DYNA geoip!prod_app/sg-01
  app.de  600 DYNA geoip!prod_app/de-01
  content 600 DYNC geoip!prod_cdn

=head1 EXAMPLE OF METAFO->GEOIP CITY-AUTO-MODE w/ LAST RESORT CNAME

  plugins => {
    geoip => {
      maps => {
        auto_map => {
          geoip_db => GeoIPCityv6.dat,
          datacenters => [dc1, dc2, dc3, dc4],
          auto_dc_coords => {
             dc1 => [ 38.9, -77 ],
             dc2 => [ 50.1, 8.7 ],
             dc3 => [ 20.2, 88.9 ],
             dc4 => [ 39.0, -20 ],
          },
          # only fail through the nearest 2 before giving up:
          auto_dc_limit => 2,
        }
      },
      resources => {
        www_real => {
          map => my_auto_map,
          service_types => [ http, xmpp ],
          dcmap => {
            dc1 => 192.0.2.100,
            dc2 => 192.0.2.101,
            dc3 => 192.0.2.102,
            dc4 => 192.0.2.103
          }
        }
      }
    },
    metafo => {
      resources => {
        www => {
          datacenters => [ real, backup ],
          dcmap => {
            real => %geoip!www_real,
            backup => backup-host.example.net.
          }
        }
      }
    }
  }

  And in the zonefile:

  ; This tries through the closest 2/4 datacenters to
  ;   the client from the geoip map, and if both of
  ;   those are down it returns a CNAME to backup-host.example.net.
  ;   for a downtime message or something:
  www DYNC metafo!www

=head1 SEE ALSO

L<gdnsd-plugin-metafo(8)>, L<gdnsd_geoip_test(1)>, L<gdnsd.config(5)>,
L<gdnsd.zonefile(5)>, L<gdnsd(8)>

The gdnsd manual.

=head1 COPYRIGHT AND LICENSE

Copyright (c) 2012 Brandon L Black <blblack@gmail.com>

This file is part of gdnsd.

gdnsd is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

gdnsd is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with gdnsd.  If not, see <http://www.gnu.org/licenses/>.

=cut
