1Copyright (C) 2004 Internet Systems Consortium, Inc. ("ISC") 2Copyright (C) 2000, 2001 Internet Software Consortium. 3See COPYRIGHT in the source root or http://isc.org/copyright.html for terms. 4 5Using the BIND 9 Simplified Database Interface 6 7This document describes the care and feeding of the BIND 9 Simplified 8Database Interface, which allows you to extend BIND 9 with new ways 9of obtaining the data that is published as DNS zones. 10 11 12The Original BIND 9 Database Interface 13 14BIND 9 has a well-defined "back-end database interface" that makes it 15possible to replace the component of the name server responsible for 16the storage and retrieval of zone data, called the "database", on a 17per-zone basis. The default database is an in-memory, red-black-tree 18data structure commonly referred to as "rbtdb", but it is possible to 19write drivers to support any number of alternative database 20technologies such as in-memory hash tables, application specific 21persistent on-disk databases, object databases, or relational 22databases. 23 24The original BIND 9 database interface defined in <dns/db.h> is 25designed to efficiently support the full set of database functionality 26needed by a name server that implements the complete DNS protocols, 27including features such as zone transfers, dynamic update, and DNSSEC. 28Each of these aspects of name server operations places its own set of 29demands on the data store, with the result that the database API is 30quite complex and contains operations that are highly specific to the 31DNS. For example, data are stored in a binary format, the name space 32is tree structured, and sets of data records are conceptually 33associated with DNSSEC signature sets. For these reasons, writing a 34driver using this interface is a highly nontrivial undertaking. 35 36 37The Simplified Database Interface 38 39Many BIND users wish to provide access to various data sources through 40the DNS, but are not necessarily interested in completely replacing 41the in-memory "rbt" database or in supporting features like dynamic 42update, DNSSEC, or even zone transfers. 43 44Often, all you want is limited, read-only DNS access to an existing 45system. For example, you may have an existing relational database 46containing hostname/address mappings and wish to provide forvard and 47reverse DNS lookups based on this information. Or perhaps you want to 48set up a simple DNS-based load balancing system where the name server 49answers queries about a single DNS name with a dynamically changing 50set of A records. 51 52BIND 9.1 introduced a new, simplified database interface, or "sdb", 53which greatly simplifies the writing of drivers for these kinds of 54applications. 55 56 57The sdb Driver 58 59An sdb driver is an object module, typically written in C, which is 60linked into the name server and registers itself with the sdb 61subsystem. It provides a set of callback functions, which also serve 62to advertise its capabilities. When the name server receives DNS 63queries, invokes the callback functions to obtain the data to respond 64with. 65 66Unlike the full database interface, the sdb interface represents all 67domain names and resource records as ASCII text. 68 69 70Writing an sdb Driver 71 72When a driver is registered, it specifies its name, a list of callback 73functions, and flags. 74 75The flags specify whether the driver wants to use relative domain 76names where possible. 77 78The callback functions are as follows. The only one that must be 79defined is lookup(). 80 81 - create(zone, argc, argv, driverdata, dbdata) 82 Create a database object for "zone". 83 84 - destroy(zone, driverdata, dbdata) 85 Destroy the database object for "zone". 86 87 - lookup(zone, name, dbdata, lookup) 88 Return all the records at the domain name "name". 89 90 - authority(zone, dbdata, lookup) 91 Return the SOA and NS records at the zone apex. 92 93 - allnodes(zone, dbdata, allnodes) 94 Return all data in the zone, for zone transfers. 95 96For more detail about these functions and their parameters, see 97bind9/lib/dns/include/dns/sdb.h. For example drivers, see 98bind9/contrib/sdb. 99 100 101Rebuilding the Server 102 103The driver module and header file must be copied to (or linked into) 104the bind9/bin/named and bind9/bin/named/include directories 105respectively, and must be added to the DBDRIVER_OBJS and DBDRIVER_SRCS 106lines in bin/named/Makefile.in (e.g. for the timedb sample sdb driver, 107add timedb.c to DBDRIVER_SRCS and timedb.@O@ to DBDRIVER_OBJS). If 108the driver needs additional header files or libraries in nonstandard 109places, the DBDRIVER_INCLUDES and DBDRIVER_LIBS lines should also be 110updated. 111 112Calls to dns_sdb_register() and dns_sdb_unregister() (or wrappers, 113e.g. timedb_init() and timedb_clear() for the timedb sample sdb 114driver) must be inserted into the server, in bind9/bin/named/main.c. 115Registration should be in setup(), before the call to 116ns_server_create(). Unregistration should be in cleanup(), 117after the call to ns_server_destroy(). A #include should be added 118corresponding to the driver header file. 119 120You should try doing this with one or more of the sample drivers 121before attempting to write a driver of your own. 122 123 124Configuring the Server 125 126To make a zone use a new database driver, specify a "database" option 127in its "zone" statement in named.conf. For example, if the driver 128registers itself under the name "acmedb", you might say 129 130 zone "foo.com" { 131 database "acmedb"; 132 }; 133 134You can pass arbitrary arguments to the create() function of the 135driver by adding any number of whitespace-separated words after the 136driver name: 137 138 zone "foo.com" { 139 database "acmedb -mode sql -connect 10.0.0.1"; 140 }; 141 142 143Hints for Driver Writers 144 145 - If a driver is generating data on the fly, it probably should 146 not implement the allnodes() function, since a zone transfer 147 will not be meaningful. The allnodes() function is more relevant 148 with data from a database. 149 150 - The authority() function is necessary if and only if the lookup() 151 function will not add SOA and NS records at the zone apex. If 152 SOA and NS records are provided by the lookup() function, 153 the authority() function should be NULL. 154 155 - When a driver is registered, an opaque object can be provided. This 156 object is passed into the database create() and destroy() functions. 157 158 - When a database is created, an opaque object can be created that 159 is associated with that database. This object is passed into the 160 lookup(), authority(), and allnodes() functions, and is 161 destroyed by the destroy() function. 162 163 164Future Directions 165 166A future release may support dynamic loading of sdb drivers. 167 168 169$Id: sdb,v 1.6 2004/03/05 05:04:54 marka Exp $ 170