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diff --git a/contrib/dlz/example/README b/contrib/dlz/example/README new file mode 100644 index 0000000..3c6ba8c --- /dev/null +++ b/contrib/dlz/example/README @@ -0,0 +1,243 @@ +OVERVIEW: + +DLZ (Dynamically Loadable Zones) is an extention to BIND 9 that +allows zone data to be retrieved directly from an external database. +There is no required format or schema. DLZ drivers exist for several +different database backends including PostgreSQL, MySQL, and LDAP and +can be written for any other. + +Historically, DLZ drivers had to be statically linked with the named +binary and were turned on via a configure option at compile time (for +example, "configure --with-dlz-ldap"). Currently, the drivers provided +in the BIND 9 tarball in contrib/dlz/drivers are still linked this way. + +However, as of BIND 9.8, it is also possible to link some DLZ modules +dynamically at runtime, via the DLZ "dlopen" driver, which acts as a +generic wrapper around a shared object that implements the DLZ API. The +"dlopen" driver is linked into named by default, so configure options are +no longer necessary unless using older DLZ drivers. + +When the DLZ module provides data to named, it does so in text format. +The response is converted to DNS wire format by named. This conversion, +and the lack of any internal caching, places significant limits on the +query performance of DLZ modules. Consequently, DLZ is not recommended +for use on high-volume servers. However, it can be used in a hidden +master configuration, with slaves retrieving zone updates via AXFR. +(Note, however, that DLZ has no built-in support for DNS notify; slaves +are not automatically informed of changes to the zones in the database.) + +CONFIGURING DLZ: + +A DLZ database is configured with a "dlz" statement in named.conf. + + dlz example { + database "dlopen driver.so <args>"; + search yes; + }; + +This specifies a DLZ module to search when answering queries; the module +is implemented in "driver.so" and is loaded at runtime by the dlopen DLZ +driver. Multiple "dlz" statements can be specified; when answering a +query, all DLZ modules with the "search" option set to "yes" will be +checked for an answer, and the best available answer will be returned +to the client. + +The "search" option in this example can be omitted, as "yes" is the +default value. If it is set to "no", then this DLZ module is *not* +searched for best-match when a query is received. Instead, zones in +this DLZ must be separately specified in a zone statement. This can +be useful when conventional zone semantics are desired but you wish +to use a different back-end storage mechanism than the standard zone +database. For example, to use a DLZ module for an NXDOMAIN redirection +zone: + + dlz other { + database "dlopen driver.so <args>"; + search no; + }; + + zone "." { + type redirect; + dlz other; + }; + +EXAMPLE DRIVER: + +This directory contains an example of an externally-lodable DLZ module, +dlz_example.c, which demonstrates the features of the DLZ API. It sets up +a single zone, whose name is configured in named.conf. The zone can answer +queries and AXFR requests, and accept DDNS updates. + +By default, at runtime, the zone implemented by this driver will contain +an SOA, NS, and a single A record at the apex. If configured in named.conf +to use the name "example.nil", then, the zone will look like this: + + example.nil. 3600 IN SOA example.nil. hostmaster.example.nil. ( + 123 900 600 86400 3600 + ) + example.nil. 3600 IN NS example.nil. + example.nil. 1800 IN A 10.53.0.1 + +The driver is also capable of retrieving information about the querying +client, and altering its response on the basis of this information. To +demonstrate this feature, the example driver responds to queries for +"source-addr.<zonename>/TXT" with the source address of the query. +Note, however, that this record will *not* be included in AXFR or ANY +responses. (Normally, this feature would be used to alter responses in +some other fashion, e.g., by providing different address records for +a particular name depending on the network from which the query arrived.) + +DYNAMIC UPDATES AND TRANSACTIONS: + +If a DLZ module wants to implement dynamic DNS updates (DDNS), the +normal calling sequence is + - dlz_newversion (start a 'transaction') + - dlz_addrdataset (add records) + - dlz_subrdataset (remove records) + - dlz_closeversion (end a 'transaction') + +However, BIND may also query the database during the transaction +(e.g., to check prerequisites), and your DLZ might need to know whether +the lookup is against the pre-existing data, or the new data. +dlz_lookup() doesn't give you access to the 'versionp' pointer +directly, so it must be passed via 'clientinfo' structure if +it is needed. + +The dlz_example.c code has sample code to show how to get the 'versionp' +pointer from within dlz_lookup(). If it's set to NULL, we query +the standard database; if non-NULL, we query against the in-flight +data within the appropriate uncommitted transaction. + +IMPLEMENTATION NOTES: + +The minimal set of type definitions, prototypes, and macros needed +for implementing a DLZ driver is in ../modules/dlz_minimal.h. Copy this +header file into your source tree when creating an external DLZ module. + +The DLZ dlopen driver provides a set of callback functions: + + - void log(int level, const char *fmt, ...); + + Writes the specified string to the named log, at the specified + log level. Uses printf() format semantics. + + - isc_result_t putrr(dns_sdlzlookup_t *lookup, const char *type, + dns_ttl_t ttl, const char *data); + + Puts a DNS resource record into the query response, which + referenced by the opaque structure 'lookup' provided by named. + + - isc_result_t putnamedrr(dns_sdlzallnotes_t *allnodes, + const char *name, const char *type, + dns_ttl_t ttl, const char *data); + + Puts a DNS resource record into an AXFR response, which is + referenced by the opaque structure 'allnodes' provided by named. + + - isc_result_t writeable_zone(dns_view_t *view, const char *zone_name); + + Allows the DLZ module to inform named that a given zone can recieve + DDNS updates. (Note: This is not currently supported for DLZ + databases that are configured as 'search no;') + +The external DLZ module can define the following functions (some of these +are mandatory, others optional). + + - int dlz_version(unsigned int *flags); + + Required for alL external DLZ modules, to indicate the version number + of the DLZ dlopen driver that this module supports. It should return + the value DLZ_DLOPEN_VERSION, which is defined in the file + contrib/dlz/modules/dlz_minimal.h and is currently 3. 'flags' is + updated to indicate capabilities of the module. In particular, if + the module is thread-safe then it sets 'flags' to include + DNS_SDLZFLAG_THREADSAFE. (Other capability flags may be added in + the future.) + + - isc_result_t dlz_create(const char *dlzname, + unsigned int argc, char *argv[], + void **dbdata, ...); + + Required for all external DLZ modules; this call initializes the + module. + + - void dlz_destroy(void *dbdata); + + Optional. If supplied, this will be called when the driver is + unloaded. + + - isc_result_t dlz_findzonedb(void *dbdata, const char *name, + dns_clientinfomethods_t *methods, + dns_clientinfo_t *clientinfo); + + Required for all external DLZ modules. This indicates whether + the DLZ module can answer for the given name. Returns ISC_R_SUCCESS + if so, and ISC_R_NOTFOUND if not. As an optimization, it can + also return ISC_R_NOMORE: this indicates that the DLZ module has + no data for the given name or for any name above it in the DNS. + This prevents named from searching for a zone cut. + + - isc_result_t dlz_lookup(const char *zone, const char *name, void *dbdata, + dns_sdlzlookup_t *lookup, + dns_clientinfomethods_t *methods, + dns_clientinfo_t *clientinfo); + + Required for all external DLZ modules. This carries out the database + lookup for a query. + + - isc_result_t dlz_allowzonexfr(void *dbdata, const char *name, + const char *client); + + Optional. Supply this if you want the module to support AXFR + for the specified zone and client. A return value of ISC_R_SUCCESS + means AXFR is allowed, any other value means it isn't. + + - isc_result_t dlz_allnodes(const char *zone, void *dbdata, + dns_sdlzallnodes_t *allnodes); + + Optional, but must be supplied dlz_allowzonexfr() is. This function + returns all nodes in the zone in order to perform a zone transfer. + + - isc_result_t dlz_newversion(const char *zone, void *dbdata, + void **versionp); + + Optional. Supply this if you want the module to support DDNS + updates. This function starts a transaction in the database. + + + - void dlz_closeversion(const char *zone, bool commit, + void *dbdata, void **versionp); + + Optional, but must be supplied if dlz_newversion() is. This function + closes a transaction. 'commit' indicates whether to commit the changes + to the database, or ignore them. + + - isc_result_t dlz_configure(dns_view_t *view, void *dbdata); + + Optional, but must be supplied in order to support DDNS updates. + + - bool dlz_ssumatch(const char *signer, const char *name, + const char *tcpaddr, const char *type, + const char *key, uint32_t keydatalen, + uint8_t *keydata, void *dbdata); + + Optional, but must be supplied in order to support DDNS updates. + + - isc_result_t dlz_addrdataset(const char *name, const char *rdatastr, + void *dbdata, void *version); + + Optional, but must be supplied in order to support DDNS updates. + Adds the data in 'rdatastr' to a database node. + + - isc_result_t dlz_subrdataset(const char *name, const char *rdatastr, + void *dbdata, void *version); + + Optional, but must be supplied in order to support DDNS updates. + Removes the data in 'rdatastr' from a database node. + + - isc_result_t dlz_delrdataset(const char *name, const char *rdatastr, + void *dbdata, void *version); + + Optional, but must be supplied in order to support DDNS updates. + Deletes all data matching the type specified in 'rdatastr' from + the database. |