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><H1
><A
NAME="BACKENDS-DETAIL"
></A
>Appendix A. Backends in detail</H1
><P
> This appendix lists several of the available backends in more detail
</P
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="PIPEBACKEND"
>A.1. PipeBackend</A
></H1
><P
> <DIV
CLASS="TABLE"
><A
NAME="AEN4489"
></A
><P
><B
>Table A-1. PipeBackend capabilities</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><COL><COL><TBODY
><TR
><TD
>Native</TD
><TD
>Yes</TD
></TR
><TR
><TD
>Master</TD
><TD
>No</TD
></TR
><TR
><TD
>Slave</TD
><TD
>No</TD
></TR
><TR
><TD
>Superslave</TD
><TD
>No</TD
></TR
><TR
><TD
>Autoserial</TD
><TD
>No</TD
></TR
><TR
><TD
>Case</TD
><TD
>Depends</TD
></TR
><TR
><TD
>Module name</TD
><TD
>pipe</TD
></TR
><TR
><TD
>Launch name</TD
><TD
>pipe</TD
></TR
></TBODY
></TABLE
></DIV
>
</P
><P
> The PipeBackend allows for easy dynamic resolution based on a 'Coprocess' which can be written in any
programming language that can read a question on standard input and answer on standard output.
</P
><P
> <DIV
CLASS="NOTE"
><P
></P
><TABLE
CLASS="NOTE"
WIDTH="100%"
BORDER="0"
><TR
><TD
WIDTH="25"
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VALIGN="TOP"
><IMG
SRC="../images/note.gif"
HSPACE="5"
ALT="Note"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
> The Pipe Backend currently does not function under FreeBSD 4.x and 5.x, probably due to unfavorable interactions between
its threading implementation and the fork system call.
</P
><P
> Interestingly, the Linux PowerDNS binary running under the Linuxulator on FreeBSD does work.
</P
></TD
></TR
></TABLE
></DIV
>
</P
><P
> To configure, the following settings are available:
<P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
>pipe-command</DT
><DD
><P
> Command to launch as backend. Mandatory.
</P
></DD
><DT
>pipe-timeout</DT
><DD
><P
> Number of milliseconds to wait for an answer from the backend. If this time is ever exceeded, the backend
is declared dead and a new process is spawned. Available since 2.7.
</P
></DD
><DT
>pipe-regex</DT
><DD
><P
> If set, only questions matching this regular expression are even sent to the backend. This makes sure that
most of PowerDNS does not slow down if you you reploy a slow backend. A query for the A record of 'www.powerdns.com'
would be presented to the regex as 'www.powerdns.com;A'. A matching regex would be '^www.powerdns.com;.*$'.
</P
><P
> To match only ANY and A queries for www.powerdns.com, use '^www.powerdns.com;(A|ANY)$'. Available since 2.8.
</P
></DD
><DT
>pipebackend-abi-version</DT
><DD
><P
> This is the version of the question format that is sent to the co-process (pipe-command) for the pipe backend.
</P
><P
> If not set the default pipebackend-abi-version is 1. When set to 2, the local-ip-address field is added
after the remote-ip-address. (the local-ip-address refers to the IP address the question was received on)
</P
></DD
></DL
></DIV
>
</P
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="PIPEBACKEND-PROTOCOL"
>A.1.1. PipeBackend protocol</A
></H2
><P
> Questions come in over a file descriptor, by default standard input. Answers
are sent out over another file descriptor, standard output by default.
</P
><DIV
CLASS="SECT3"
><H3
CLASS="SECT3"
><A
NAME="AEN4545"
>A.1.1.1. Handshake</A
></H3
><P
> PowerDNS sends out 'HELO\t1', indicating that it wants to speak the
protocol as defined in this document, version 1.
A PowerDNS CoProcess must then send out a banner, prefixed by 'OK\t',
indicating it launched successfully. If it does not support the indicated
version, it should respond with FAIL, but not exit. Suggested behaviour is
to try and read a further line, and wait to be terminated.
</P
></DIV
><DIV
CLASS="SECT3"
><H3
CLASS="SECT3"
><A
NAME="AEN4548"
>A.1.1.2. Questions</A
></H3
><P
> Questions come in three forms and are prefixed by a tag indicating the kind:
<P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
>Q</DT
><DD
><P
> Regular queries
</P
></DD
><DT
>AXFR</DT
><DD
><P
> List requests, which mean that an entire zone should be listed
</P
></DD
><DT
>PING</DT
><DD
><P
> Check if the coprocess is functioning
</P
></DD
></DL
></DIV
>
The question format:
pipebackend-abi-version = 1 [default]
<PRE
CLASS="SCREEN"
>type qname qclass qtype id remote-ip-address</PRE
>
pipebackend-abi-version = 2
<PRE
CLASS="SCREEN"
>type qname qclass qtype id remote-ip-address local-ip-address</PRE
>
Fields are tab separated, and terminated with a single \n. The remote-ip-address is the IP address
of the nameserver asking the question; the local-ip-address is the IP address on which the question
was received.
Type is the tag above, qname is the domain the question is about. qclass is
always 'IN' currently, denoting an INternet question. qtype is the kind of
information desired, the record type, like A, CNAME or AAAA. id can be
specified to help your backend find an answer if the id is already known
from an earlier query. You can ignore it.
remote-ip-address is the ip-address of the nameserver asking the question.
local-ip-address is the ip-address that was querried locally.
</P
></DIV
><DIV
CLASS="SECT3"
><H3
CLASS="SECT3"
><A
NAME="AEN4566"
>A.1.1.3. Answers</A
></H3
><P
> Each answer starts with a tag, possibly followed by a TAB and more data.
<P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
>DATA</DT
><DD
><P
> Indicating a successful line of DATA
</P
></DD
><DT
>END</DT
><DD
><P
> Indicating the end of an answer - no further data
</P
></DD
><DT
>FAIL</DT
><DD
><P
> Indicating a lookup failure. Also serves as 'END'. No further data.
</P
></DD
><DT
>LOG</DT
><DD
><P
> For specifying things that should be logged. Can only be sent after
a query and before an END line. After the tab, the message to be
logged
</P
></DD
></DL
></DIV
>
So letting it be known that there is no data consists if sending 'END'
without anything else.
The answer format:
<PRE
CLASS="SCREEN"
>DATA qname qclass qtype ttl id content </PRE
>
'content' is as specified in <A
HREF="types.html"
>Chapter 17</A
>.
A sample dialogue may look like this:
<PRE
CLASS="SCREEN"
>Q www.ds9a.nl IN CNAME -1 213.244.168.210
DATA www.ds9a.nl IN CNAME 3600 1 ws1.ds9a.nl
Q ws1.ds9a.nl IN CNAME -1 213.244.168.210
END
Q wd1.ds9a.nl IN A -1 213.244.168.210
DATA ws1.ds9a.nl IN A 3600 1 1.2.3.4
DATA ws1.ds9a.nl IN A 3600 1 1.2.3.5
DATA ws1.ds9a.nl IN A 3600 1 1.2.3.6
END</PRE
>
This would correspond to a remote webserver 213.244.168.210 wanting to
resolve the IP address of www.ds9a.nl, and PowerDNS traversing the CNAMEs to
find the IP addresses of ws1.ds9a.nl
Another dialogue might be:
<PRE
CLASS="SCREEN"
>Q ds9a.nl IN SOA -1 213.244.168.210
DATA ds9a.nl IN SOA 86400 1 ahu.ds9a.nl ...
END
AXFR 1
DATA ds9a.nl IN SOA 86400 1 ahu.ds9a.nl ...
DATA ds9a.nl IN NS 86400 1 ns1.ds9a.nl
DATA ds9a.nl IN NS 86400 1 ns2.ds9a.nl
DATA ns1.ds9a.nl IN A 86400 1 213.244.168.210
DATA ns2.ds9a.nl IN A 86400 1 63.123.33.135
.
.
END</PRE
>
This is a typical zone transfer.
</P
></DIV
><DIV
CLASS="SECT3"
><H3
CLASS="SECT3"
><A
NAME="AEN4590"
>A.1.1.4. Sample perl backend</A
></H3
><P
> <PRE
CLASS="SCREEN"
>#!/usr/bin/perl -w
# sample PowerDNS Coprocess backend
#
use strict;
$|=1; # no buffering
my $line=<>;
chomp($line);
unless($line eq "HELO\t1") {
print "FAIL\n";
print STDERR "Recevied '$line'\n";
<>;
exit;
}
print "OK Sample backend firing up\n"; # print our banner
while(<>)
{
print STDERR "$$ Received: $_";
chomp();
my @arr=split(/\t/);
if(@arr<6) {
print "LOG PowerDNS sent unparseable line\n";
print "FAIL\n";
next;
}
my ($type,$qname,$qclass,$qtype,$id,$ip)=split(/\t/);
if(($qtype eq "A" || $qtype eq "ANY") && $qname eq "webserver.example.com") {
print STDERR "$$ Sent A records\n";
print "DATA $qname $qclass A 3600 -1 1.2.3.4\n";
print "DATA $qname $qclass A 3600 -1 1.2.3.5\n";
print "DATA $qname $qclass A 3600 -1 1.2.3.6\n";
}
elsif(($qtype eq "CNAME" || $qtype eq "ANY") && $qname eq "www.example.com") {
print STDERR "$$ Sent CNAME records\n";
print "DATA $qname $qclass CNAME 3600 -1 webserver.example.com\n";
}
elsif($qtype eq "MBOXFW") {
print STDERR "$$ Sent MBOXFW records\n";
print "DATA $qname $qclass MBOXFW 3600 -1 powerdns\@example.com\n";
}
print STDERR "$$ End of data\n";
print "END\n";
}
</PRE
>
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distrib
>
Mandriva
>
2010.1
>
i586
>
media
>
contrib-updates
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by-pkgid
>
563affe035311228f138962d4d47d4fd
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