Preset variables

LUA rules run within the same environment as described in DNS Modes of Operation.

The Lua snippets can query the following variables:

Query variables

dh
The DNSHeader of the received query.
dnssecOK
A boolean describing if the DNSSEC OK (DO) bit was set in the query.
ednsPKTSize
The advertised EDNS buffer size.
qname
The name of the requested record. This is a DNSName.
zone
The zone this LUA record is in. This is a DNSName.
zoneid
The id of the zone. This is an integer.
tcp
Whether or not the query was received over TCP.

Client variables

ecswho
The EDNS Client Subnet, should one have been set on the query. Unset otherwise. This is a Netmask.
bestwho
In absence of ECS, this is set to the IP address of requesting resolver. Otherwise set to the network part of the EDNS Client Subnet supplied by the resolver. This is a ComboAddress.
who
IP address of requesting resolver as a ComboAddress.
localwho
IP address (including port) of socket on which the question arrived.

Functions available

Record creation functions

ifportup(portnum, addresses[, options])

Simplistic test to see if an IP address listens on a certain port. This will attempt a TCP connection on port portnum and consider it available if the connection establishes. No data will be sent or read on that connection. Note that both IPv4 and IPv6 addresses can be tested, but that it is an error to list IPv4 addresses on an AAAA record, or IPv6 addresses on an A record.

Will return a single address from the set of available addresses. If no address is available, will return a random element of the set of addresses supplied for testing.

Parameters:
  • portnum (int) – The port number to test connections to.
  • addresses ({str}) – The list of addresses to check connectivity for.
  • options – Table of options for this specific check, see below.

Various options can be set in the options parameter:

  • selector: used to pick the address(es) from the list of available addresses. Choices include ‘pickclosest’, ‘random’, ‘hashed’, ‘all’ (default ‘random’).
  • backupSelector: used to pick the address(es) from all addresses if all addresses are down. Choices include ‘pickclosest’, ‘random’, ‘hashed’, ‘all’ (default ‘random’).
  • source: Source address to check from
  • timeout: Maximum time in seconds that you allow the check to take (default 2)
ifurlup(url, addresses[, options])

More sophisticated test that attempts an actual http(s) connection to url. In addition, a list of sets of IP addresses can be supplied. The first set with at least one available address is selected. The selector then selects from the subset of available addresses of the selected set. An URL is considered available if the HTTP response code is 200 and optionally if the content matches the stringmatch option.

Parameters:
  • url (string) – The url to retrieve.
  • addresses – List of sets of addresses to check the URL on.
  • options – Table of options for this specific check, see below.

Various options can be set in the options parameter:

  • selector: used to pick the address(es) from the subset of available addresses of the selected set. Choices include ‘pickclosest’, ‘random’, ‘hashed’, ‘all’ (default ‘random’).
  • backupSelector: used to pick the address from all addresses if all addresses are down. Choices include ‘pickclosest’, ‘random’, ‘hashed’, ‘all’ (default ‘random’).
  • source: Source address to check from
  • timeout: Maximum time in seconds that you allow the check to take (default 2)
  • stringmatch: check url for this string, only declare ‘up’ if found
  • useragent: Set the HTTP “User-Agent” header in the requests. By default it is set to “PowerDNS Authoritative Server”
  • byteslimit: Limit the maximum download size to byteslimit bytes (default 0 meaning no limit).

An example of a list of address sets:

ifurlup("https://example.com/", { {"192.0.2.20", "203.0.113.4"}, {"203.0.113.2"} })
ifurlextup(groups-of-address-url-pairs[, options])

Very similar to ifurlup, but the returned IPs are decoupled from their external health check URLs. This is useful when health checking already happens elsewhere, and that state is exposed over HTTP(S). Health checks are considered positive if the HTTP response code is 200 and optionally if the content matches the stringmatch option.

Options are identical to those for ifurlup.

Example:

ifurlextup({{['192.168.0.1']='https://example.com/',['192.168.0.2']='https://example.com/404'}})

Example with two groups:

ifurlextup({{['192.168.0.1']='https://example.net/404',['192.168.0.2']='https://example.com/404'}, {['192.168.0.3']='https://example.net/'}})"

The health checker will look up the first two URLs (using normal DNS resolution to find them - whenever possible, use URLs with IPs in them). The 404s will cause the first group of IPs to get marked as down, after which the URL in the second group is tested. The third IP will get marked up assuming https://example.net/ responds with HTTP response code 200.

pickrandom(values)

Returns a random value from the list supplied.

Parameters:values – A list of strings such as IPv4 or IPv6 address.

This function also works for CNAME or TXT records.

pickrandomsample(number, values)

Returns N random values from the list supplied.

Parameters:
  • number – Number of values to return
  • values – A list of strings such as IPv4 or IPv6 address.

This function also works for CNAME or TXT records.

pickhashed(values)

Based on the hash of bestwho, returns a random value from the list supplied.

Parameters:values – A list of strings such as IPv4 or IPv6 address.

This function also works for CNAME or TXT records.

pickclosest(addresses)

Returns IP address deemed closest to the bestwho IP address.

Parameters:addresses – A list of strings with the possible IP addresses.
latlon()

Returns text listing fractional latitude/longitude associated with the bestwho IP address.

latlonloc()

Returns text in LOC record format listing latitude/longitude associated with the bestwho IP address.

closestMagic()

Suitable for use as a wildcard LUA A record. Will parse the query name which should be in format:

192-0-2-1.192-0-2-2.198-51-100-1.magic.v4.powerdns.org

It will then resolve to an A record with the IP address closest to bestwho from the list of supplied addresses.

In the magic.v4.powerdns.org this looks like:

*.magic.v4.powerdns.org    IN    LUA    A    "closestMagic()"

In another zone, a record is then present like this:

www-balanced.powerdns.org    IN    CNAME    192-0-2-1.192-0-2-2.198-51-100-1.magic.v4.powerdns.org

This effectively opens up your server to being a ‘geographical load balancer as a service’.

Performs no uptime checking.

all(values)

Returns all values.

Parameters:values – A list of strings such as IPv4 or IPv6 address.

This function also works for CNAME or TXT records.

view(pairs)

Shorthand function to implement ‘views’ for all record types.

Parameters:pairs – A list of netmask/result pairs.

An example:

view.v4.powerdns.org    IN    LUA    A ("view({                                  "
                                        "{ {'192.168.0.0/16'}, {'192.168.1.54'}},"
                                        "{ {'0.0.0.0/0'}, {'192.0.2.1'}}         "
                                        " }) " )

This will return IP address 192.168.1.54 for queries coming from 192.168.0.0/16, and 192.0.2.1 for all other queries.

This function also works for CNAME or TXT records.

pickchashed(values)

Based on the hash of bestwho, returns a string from the list supplied, as weighted by the various weight parameters and distributed consistently. Performs no uptime checking.

Parameters:values – table of weight, string (such as IPv4 or IPv6 address).

This function works almost like pickwhashed() while bringing the following properties: - reordering the list of entries won’t affect the distribution - updating the weight of an entry will only affect a part of the distribution - because of the previous properties, the CPU and memory cost is a bit higher than pickwhashed()

Hashes will be pre computed the first time such a record is hit and refreshed if needed. If updating the list is done often, the cash may grow. A cleanup routine is performed every lua-consistent-hashes-cleanup-interval seconds (default 1h) and cleans cached entries for records that haven’t been used for lua-consistent-hashes-expire-delay seconds (default 24h)

An example:

mydomain.example.com    IN    LUA    A ("pickchashed({                             "
                                        "        {15,  "192.0.2.1"},               "
                                        "        {100, "198.51.100.5"}             "
                                        "})                                        ")
pickwhashed(values)

Based on the hash of bestwho, returns a string from the list supplied, as weighted by the various weight parameters. Performs no uptime checking.

Parameters:values – table of weight, string (such as IPv4 or IPv6 address).

Because of the hash, the same client keeps getting the same answer, but given sufficient clients, the load is still spread according to the weight factors.

This function also works for CNAME or TXT records.

An example:

mydomain.example.com    IN    LUA    A ("pickwhashed({                             "
                                        "        {15,  "192.0.2.1"},               "
                                        "        {100, "198.51.100.5"}             "
                                        "})                                        ")
picknamehashed(values)

Based on the hash of the DNS record name, returns a string from the list supplied, as weighted by the various weight parameters. Performs no uptime checking.

Parameters:values – table of weight, string (such as IPv4 or IPv6 address).

This allows basic persistent load balancing across a number of backends. It means that test.mydomain.example.com will always resolve to the same IP, but test2.mydomain.example.com may go elsewhere. This function is only useful for wildcard records.

This works similar to round-robin load balancing, but has the advantage of making traffic for the same domain always end up on the same server which can help cache hit rates.

This function also works for CNAME or TXT records.

An example:

*.mydomain.example.com    IN    LUA    A ("picknamehashed({                        "
                                          "        {15,  "192.0.2.1"},             "
                                          "        {100, "198.51.100.5"}           "
                                          "})                                      ")
pickwrandom(values)

Returns a random string from the list supplied, as weighted by the various weight parameters. Performs no uptime checking.

Parameters:values – table of weight, string (such as IPv4 or IPv6 address).

See pickwhashed() for an example.

This function also works for CNAME or TXT records.

Reverse DNS functions

Warning

For createForward() and createForward6(), we recommend filtering with filterForward(), to prevent PowerDNS from generating A/AAAA responses to addresses outside of your network. Not limiting responses like this may, in some situations, help attackers with impersonation and attacks like such as cookie stealing.

createReverse(format[, exceptions])

Used for generating default hostnames from IPv4 wildcard reverse DNS records, e.g. *.0.0.127.in-addr.arpa

See createReverse6() for IPv6 records (ip6.arpa)

See createForward() for creating the A records on a wildcard record such as *.static.example.com

Returns a formatted hostname based on the format string passed.

Parameters:
  • format – A hostname string to format, for example %1%.%2%.%3%.%4%.static.example.com.
  • exceptions – An optional table of overrides. For example {['10.10.10.10'] = 'quad10.example.com.'} would, when generating a name for IP 10.10.10.10, return quad10.example.com instead of something like 10.10.10.10.example.com.

Formatting options:

  • %1% to %4% are individual octets
    • Example record query: 1.0.0.127.in-addr.arpa
    • %1% = 127
    • %2% = 0
    • %3% = 0
    • %4% = 1
  • %5% joins the four decimal octets together with dashes
    • Example: %5%.static.example.com is equivalent to %1%-%2%-%3%-%4%.static.example.com
  • %6% converts each octet from decimal to hexadecimal and joins them together
    • Example: A query for 15.0.0.127.in-addr.arpa
    • %6 would be 7f00000f (127 is 7f, and 15 is 0f in hexadecimal)

Example records:

*.0.0.127.in-addr.arpa IN    LUA    PTR "createReverse('%1%.%2%.%3%.%4%.static.example.com')"
*.1.0.127.in-addr.arpa IN    LUA    PTR "createReverse('%5%.static.example.com')"
*.2.0.127.in-addr.arpa IN    LUA    PTR "createReverse('%6%.static.example.com')"

When queried:

# -x is syntactic sugar to request the PTR record for an IPv4/v6 address such as 127.0.0.5
# Equivalent to dig PTR 5.0.0.127.in-addr.arpa
$ dig +short -x 127.0.0.5 @ns1.example.com
127.0.0.5.static.example.com.
$ dig +short -x 127.0.1.5 @ns1.example.com
127-0-0-5.static.example.com.
$ dig +short -x 127.0.2.5 @ns1.example.com
7f000205.static.example.com.
createForward()

Used to generate the reverse DNS domains made from createReverse()

Generates an A record for a dotted or hexadecimal IPv4 domain (e.g. 127.0.0.1.static.example.com)

It does not take any parameters, it simply interprets the zone record to find the IP address.

An example record for zone static.example.com:

*.static.example.com    IN    LUA    A "createForward()"

This function supports the forward dotted format (127.0.0.1.static.example.com), and the hex format, when prefixed by two ignored characters (ip40414243.static.example.com)

When queried:

$ dig +short A 127.0.0.5.static.example.com @ns1.example.com
127.0.0.5

Since 4.8.0: the hex format can be prefixed by any number of characters (within DNS label length limits), including zero characters (so no prefix).

createReverse6(format[, exceptions])

Used for generating default hostnames from IPv6 wildcard reverse DNS records, e.g. *.1.0.0.2.ip6.arpa

For simplicity purposes, only small sections of IPv6 rDNS domains are used in most parts of this guide, as a full ip6.arpa record is around 80 characters long

See createReverse() for IPv4 records (in-addr.arpa)

See createForward6() for creating the AAAA records on a wildcard record such as *.static.example.com

Returns a formatted hostname based on the format string passed.

Parameters:
  • format – A hostname string to format, for example %33%.static6.example.com.
  • exceptions – An optional table of overrides. For example {['2001:db8::1'] = 'example.example.com.'} would, when generating a name for IP 2001:db8::1, return example.example.com instead of something like 2001--db8.example.com.

Formatting options:

  • %1% to %32% are individual characters (nibbles)
    • Example PTR record query: a.0.0.0.1.0.0.2.ip6.arpa
    • %1% = 2
    • %2% = 0
    • %3% = 0
    • %4% = 1
  • %33% converts the compressed address format into a dashed format, e.g. 2001:a::1 to 2001-a--1
  • %34% to %41% represent the 8 uncompressed 2-byte chunks
    • Example: PTR query for 2001:a:b::123
    • %34% - returns 2001 (chunk 1)
    • %35% - returns 000a (chunk 2)
    • %41% - returns 0123 (chunk 8)

Example records:

*.1.0.0.2.ip6.arpa IN    LUA    PTR "createReverse6('%33%.static6.example.com')"
*.2.0.0.2.ip6.arpa IN    LUA    PTR "createReverse6('%34%.%35%.static6.example.com')"

When queried:

# -x is syntactic sugar to request the PTR record for an IPv4/v6 address such as 2001::1
# Equivalent to dig PTR 1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.b.0.0.0.a.0.0.0.1.0.0.2.ip6.arpa
# readable version:     1.0.0.0 .0.0.0.0 .0.0.0.0 .0.0.0.0 .0.0.0.0 .b.0.0.0 .a.0.0.0 .1.0.0.2 .ip6.arpa

$ dig +short -x 2001:a:b::1 @ns1.example.com
2001-a-b--1.static6.example.com.

$ dig +short -x 2002:a:b::1 @ns1.example.com
2002.000a.static6.example.com
createForward6()

Used to generate the reverse DNS domains made from createReverse6()

Generates an AAAA record for a dashed compressed IPv6 domain (e.g. 2001-a-b--1.static6.example.com)

It does not take any parameters, it simply interprets the zone record to find the IP address.

An example record for zone static.example.com:

*.static6.example.com    IN    LUA    AAAA "createForward6()"

This function supports the dashed compressed format (i.e. 2001-a-b--1.static6.example.com), and the dot-split uncompressed format (2001.db8.6.5.4.3.2.1.static6.example.com)

When queried:

$ dig +short AAAA 2001-a-b--1.static6.example.com @ns1.example.com
2001:a:b::1

Since 4.8.0: a non-split full length format (20010002000300040005000600070db8.example.com) is also supported, optionally prefixed, in which case the last 32 characters will be considered.

filterForward(address, masks[, fallback])

New in version 4.5.0.

Used for limiting the output of createForward() and createForward6() to a set of netmasks.

Parameters:
  • address – A string containing an address, usually taken directly from createForward: or :func:`createForward6().
  • masks – A NetmaskGroup; any address not matching the NMG will be replaced by the fallback address.
  • fallback – A string containing the fallback address. Defaults to 0.0.0.0 or ::.

Example:

*.static4.example.com IN LUA A "filterForward(createForward(), newNMG({'192.0.2.0/24', '10.0.0.0/8'}))"

Since 4.9.0: if the fallback parameter is an empty string, filterForward returns an empty set, yielding a NODATA answer. You cannot combine this feature with DNSSEC.

Helper functions

asnum(number)
asnum(numbers)

Returns true if the bestwho IP address is determined to be from any of the listed AS numbers.

Parameters:
  • number (int) – An AS number
  • numbers ([int]) – A list of AS numbers
country(country)
country(countries)

Returns true if the bestwho IP address of the client is within the two letter ISO country code passed, as described in GeoIP backend.

Parameters:
  • country (string) – A country code like “NL”
  • countries ([string]) – A list of country codes
countryCode()

Returns two letter ISO country code based bestwho IP address, as described in GeoIP backend. If the two letter ISO country code is unknown “–” will be returned.

region(region)
region(regions)

Returns true if the bestwho IP address of the client is within the two letter ISO region code passed, as described in GeoIP backend.

Parameters:
  • region (string) – A region code like “CA”
  • regions ([string]) – A list of regions codes
regionCode()

Returns two letter ISO region code based bestwho IP address, as described in GeoIP backend. If the two letter ISO region code is unknown “–” will be returned.

continent(continent)
continent(continents)

Returns true if the bestwho IP address of the client is within the continent passed, as described in GeoIP backend.

Parameters:
  • continent (string) – A continent code like “EU”
  • continents ([string]) – A list of continent codes
continentCode()

Returns two letter ISO continent code based bestwho IP address, as described in GeoIP backend. If the two letter ISO continent code is unknown “–” will be returned.

netmask(netmasks)

Returns true if bestwho is within any of the listed subnets.

Parameters:netmasks ([string]) – The list of IP addresses to check against
dblookup(name, type)

New in version 4.9.0.

Does a database lookup for name and type, and returns a (possibly empty) array of string results.

Please keep the following in mind:

  • it does not evaluate any LUA code found
  • if you needed just one string, perhaps you want dblookup('www.example.org', pdns.A)[1] to take the first item from the array
  • some things, like ifurlup, don’t like empty tables, so be careful not to accidentally look up a name that does not have any records of that type, if you are going to use the result in ifurlup

Example usage:

www IN LUA A "ifurlup('https://www.example.com/', {dblookup('www1.example.com', pdns.A), dblookup('www2.example.com', pdns.A), dblookup('www3.example.com', pdns.A)})"
Parameters:
  • name (string) – Name to look up in the database
  • type (int) – DNS type to look for